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laughton

Get Squared! Use a Trench Map

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laughton

I assembled this information in part to deal with some of the issues on the trench map errors made by the 18th Labour Company that were involved in the 2 British Cases (2nd Lt. Kipling & 2nd Lt. Law) and the corresponding and closely link cases of the 2 Canadian Cases (Lt. McDonald & Lt. Wylie). It became apparent to me that we needed to know more about the origins of the trench maps and the "missing pieces" when the "Squared Maps" changed to the "Revised Squaring" approach. Unlike Dr. Peter Chasseaud, I am no expert on this topic but I soon found that someone needed to explain (or try to explain) more about the transformation process. This is my start on that assignment. I welcome any comments, questions and criticisms - as long as you tell me who you are when you make them.

GET SQUARED! USE A TRENCH MAP
Part I
Welcome to Trench Map “Boot Camp”. I am taking you back to the basics and then we will go on from there. You can download this post in PDF Format as well.
Trench Map Letters and Numbers
In the beginning of the transformation of the trench maps from the French (1:80,000) or Belgian (1:40,000) to the British system, each 1:40,000 scale maps was created using 24 squares each 1,000 yards by 1,000 yards (A-X). That gave the total area of any square as 1,000,000 square yards. Each of those squares was divided into 36 sub-squares (1-36) and then each sub-square was divided into 4 sectors (a, b, c, d). The reference for this is the work of Dr. Peter Chasseaud as detailed on the IWM Trench Map DVD "Understanding a Trench Map".
It appears that there is a restriction on the image posting and ability to control size so I have just left the links to the images. You can download the file with the images intact at the PDF link provided above.

“The British 1:40,000 sheet, covered by this squaring system, was subdivided into twenty-four 6,000-yard squares (or 6,000-yard x 5,000-yard rectangles in the case of the top and bottom rows) each designated by a capital letter (A–X); each of these squares was subdivided into thirty or thirty-six 1,000-yard squares, each designated by a number (1–36); these 1,000-yard squares were further subdivided into four 500-yard subsquares, designated a, b, c and d.”

The main map example thus shows the 24 squares from A to X, which for this demonstration I have broken down into three colour codes. The reason for the different colours will become apparent as this example continues.
You will note from the Chasseaud statement that it says it is a mixture of 24 squares and rectangles (A-X) but it does not say some squares and two different sizes of rectangles, but that is exactly what happens when you convert the French (metric = metres) maps into English (imperial = yards) maps. At the beginning, however, they were all squares and they all were subdivided into 36 smaller squares.
To make the Imperial version of the maps conform to the Metric maps, it was necessary to change some of the Big Squares (A-X) into Big Rectangles. This is where the colour coding in the first map comes into play, as here is what happened:
The initial maps that were made were intact and had all the squares, however to date I have not been able to locate one of those maps. If you have one and can provide images, please email me at cefmatrix@gmail.com, for which I will be eternally grateful!
The initial maps were intact and were not missing the top or bottom row or the one-half of each square on the left and right sides. Initially, every square had 4 sub-squares designated a, b, c, and d. It was during the revision process, to make the Imperial maps coincide with the Metric maps that the changes were made.
The best way to see where the changes were made is to look at a real trench map. In this case, I have used the McMaster Map for Lens and Vimy, which in overall appears in four (4) larger sectors of NW, NE, SW and SE:
The sub-areas (either squares or rectangles) that are in each of these are:
If you look at the Lens 1:40,000 trench map you will see that square A only shows 30 of the 36 sub-squares, so one might ask where the other six went (30-36 are missing). The same applies to square S at the bottom of the left side. As you look further you will note that all of the top and bottom rows have 30 squares instead of 36. If you look at square H you will see that there are 36 sub-squares. Also if you look down the side, you will see that there are only one-half of each square for the left side (1, 7, 13, 19, 25 and 31) and the same for the right side (6, 12, 18,24,30,36), but drop the 31 and 36 on the top and bottom rows.
We can show an enlargement of Sector A to show how it as a BLUE SUB-SECTOR has only 5 rows instead of 6 and does not show the left side of the outer quadrants:
Some references report simply that the squares A-X are 6,000 x 6,000 yards (6,000 yards square). Others clarify that there is an exception in that the top and bottom rows are 6,000 x 5,000 yards. As I have shown here, you need to go one step further to clarify that the "special" squares A, S, F and X are only 5,500 yards x 5,000 yards and the “special” squares G, M, L, R are 5,500 yards x 6,000 yards. That means the internal squares with no outer boundary are 36,000,000 square yards (H, I, J, K, N, O, P, Q); those with only a north or south boundary are 30,000,000 square yards (B, C, D, E T, U, V, W), the four middle sides with only an east or west boundary are 33,000,000 square yards (G, M, L, R) and the four corner squares with multiple boundaries are 27,500,000 square yards (A, F, S, X).
The McMaster Trench Maps database has a few examples of where they have combined maps, one of which is Bethune [battle of Neuve Chapelle]. Here the map contains parts of four (4) maps, including 36a SE, 36 SW, 36b NE, and 36a NW. I have marked the overlap area with the blue box, which shows you have:
In hindsight, I believe it would have been better when they removed the top row of the map that they followed the same procedure they did with the bottom row so that the sub-squares were numbered 7 to 36 instead of 1 to 30. That would have demonstrated that it was the top row that was overlapped with the map above, the same as what is depicted on the bottom where 31 to 36 is missing and is on the map below to match what is shown as Map 51b Squares A1 to A6.
I would agree with those that say that the maps that were routinely used during the war only show half the sub-squares on the left (b, d) and right (a, c) sides of the map but I do not agree that they never existed. They are still there today in the original maps but they are not shown in the maps that were used during the war. The same applies to the top and bottom of the maps, where the rows overlap. If you were to take the full map before it was used to create the "Revised Squared Map" in late 1914 then they existed. Dr. Chasseaud refers to this as “the revised system of squaring”. The original concept remains intact.
If you refer to the example shown above where the four maps overlap, the original maps prior to the revised system of squaring would have been as follows:
With the Revised System of Squaring the right side of the X-F box disappeared, as did the left side of the S-A box.
The Original Maps
Details on the history of the British Trench Maps of the Great War are provided on the web site of the National Library of Scotland. They refer to the original maps as being Belgian 1:40,000 maps in a numbered series from 1 to 72, to which letters were added as the maps were expanded to cover France. This explains why map 36c is the same as map 44a, as the Belgian map 36 was expanded to the west to make 36a, to the southwest to make 36b and directly to the south to make 36c. Likewise Belgian map 44 if expanded to the west would be 44a, which is the same location as 36c. This is clear when you look at the general layout of the maps on the front page of the McMaster Map Lloyd Reeds Collection, as depicted in the image that follows.
The original trench map grid system implemented in 1914 is reported to have been based on the sub-division of each of the 1:40,000 sheets into 5,000 yard squares (5,000 yards x 5,000 yards). My previous colour analysis of the maps provides us with the ability to calculate the coverage of the maps in the original squaring format versus the system of revised squaring.
The original squared map system consisted of the full complement of 36 squares each 5,000 yards by 5,000 yards for a total of 900 million square yards. That shows that the revised squaring maps were approximately 85.6 % of the original maps.
The revised squaring maps were not available to the British Expeditionary Force (BEF) at the start of the Great War in August 1914. They instead had to rely on the original Belgian 1:40,000 scale maps or the 1:80,000 scale French maps. I am still looking for copies or images of each of those styles of maps.
Some indication of the size of the original maps can be gleaned from the larger scale 1:250,000, which I fortunately have in my collection. Each of these maps is marked 1-10 on the vertical border and A-N on the horizontal border. Some of the printed maps are 1-12 on the vertical border; however these do show the overlap onto the next sheet, so we can assume the 1-10 vertical border was standard.
These maps have a scale of 1 centimetre to 2.5 kilometres (1:250,000 scale) or 1 inch to 3.95 miles, so it is apparent these were metric maps. Each horizontal grid A-N (14 blocks) is 5 centimetres (12.5 kilometres) for a total horizontal grid of 175 kilometres. The vertical grid (1-10) is 125 kilometres. Had they used the metric system in the revised squaring approach, instead of converting to imperial then all of this would have been avoided, as the squares would have matched the original Belgian and French maps.
To compare how a revised squaring map at the 1:40,000 scale compared to the 1:250,000 of North West Europe (Sheet 4), I marked out exactly where the limits of France Sheet 51b was on an extract of the 1:250,000 map. The orange square in the extract of the 1:25,000 map is the perimeter of the 1:40,000 51b trench map.
That gave me an inlaid square that was 12.8 cm horizontal (32,000 metres) and 8.05 cm vertical (20,125 metres). From the earlier squares analysis we know that the 51b map is 35,000 yards on the horizontal and 22,000 yards on the vertical. The results are quite comparable:
The Revised Squaring Sub-Maps
Each of the 1:40,000 Trench Maps is divided into four (4) 1:20,000 trench maps, as I showed in an earlier table as NW, NE, SW, and SE. Sticking with the 51b example we can show the 51b NW map that includes all of the sectors A, B, C, G, H and I: (the green lines and black letters were added for clarity)
Each of these 1:20,000 sub-maps is then broken down into NW1, NW2, NW3 and NW4 with a 1:10,000 scale. These like the revised squaring maps are split in the middle of B4 and H4, as shown here looking at only NW1: (earlier edition trenches)
Introducing Latitude and Longitude
It would be remiss not to mention the importance of latitude and longitude as an important component of understanding the trench maps. Not only was this important to those using the maps for large scale offensives in the Great War but now 100 years later for those using GPS and Google Earth to find locations and plot trench overlays. On the small scale the impact is negligible but on the larger scale it is immense. This importance was introduced to the CEFSG Matrix project in 2010 by Member Dave MacLeod (CWS Teacher) who teaches Canadian World Studies at Exeter District High School (my alma mater).
Each co-ordinate on a trench map can be linked to longitude and latitude so that it can be used with a modern day GPS unit. Each of these co-ordinates is sub-divided into Degrees, Minutes and Seconds. In a general sense, 1 Minute of Latitude is approximately equal to 1 Nautical Mile (6,076 feet). The longitude issue is trickier to interpret. The simplest way to visualize that is to look at a GLOBE where you can see that the longitudes are 1 nautical mile apart at the equator but they merge as they go to the north and south poles where they are 0 nautical miles apart. For details on this phenomenon, please see the web site of the RASC Calgary Centre, which is partially exhibited here:
You can find the approximate GPS coordinates for any set of Great War Trench Maps with the on-line Great War British Trench Map Coordinates Converter. If you need to convert GPS readings for Latitude and Longitude you can do this on-line with the GPS Visualizer Coordinate Calculator. To calculate the longitude distance at given latitude you need to know the cosine of the latitude which you can also calculate on-line with the Cosine Calculator.
Part II
The puzzle that still remains is what latitude and longitude was used to make the early trench maps and how did they go from the earth as an “oblate spheroid” to a flat plane? To answer that question we must go back to the original maps.
The Origins of the Maps
To demonstrate the difference between the trench maps shown on a flat plane to that of the oblate spheroid, I refer to a classic imaged as provided in "Manual of Map Reading, Photo Reading and Field Sketching. The War Office. 1929". The book was written as a training manual for candidates for commission in the British Regular Army. Several inferences in the book date it back to 1917, with the main text printed in 1929. The version I have is #4 and was printed August 31, 1939.
The comparison of the two layouts is perhaps the simplest way to demonstrate the problems of placing locations on a spheroid earth on a flat plane. On the small scale the differences are “acceptable” but on the larger scale very critical. You will see quickly, if you look at the map coordinates for the latitude and longitude in the corners that they vary.
One of the first places I erred when I went to look at the circa 1914 Belgian maps was I assumed the Longitude was at the British Prime Meridian which runs through Greenwich, England. As it turns out, the Belgian maps are based on the prime meridian being in the centre of Brussels and thus the corresponding French maps may be based on a prime meridian in Paris. An analysis of the maps reveals the French maps are consistent with the Belgian maps; as the lower left reading in all the maps that are in a straight line with Map 28, such as 51b have the same distance of 116,000 m W and the lower left corner and 84,000 m W in the lower right corner. Map 51b which adjoins 51a has 84,000 m W on the lower left and 52,000 m W on the lower right. That is the 32,000 m distance so these maps really are metric still with imperial measurements for the grid. The imperial squares take up 35,000 yards (32,004 metres) so it appears they decided to just forgo the 2 meter difference on each side of the map.
The horizontal grid marks for map 28 are 57,240 m at the top and 37,240 m at the bottom, so the maps are 20,000 m on the vertical. That explains the tiny blank space on the top and bottom margin of each map, as the squares take up a vertical distance of 22,000 yards (20116.8 m) so the blank "lost" space is 58.4 m on the top and bottom of each map.
I was always of the impression that there was 1/2 of each square on the left and right side of each map. If you calculate the difference between the markers on the top or bottom of any map you will find it is 32,000 metres (approximately 34,996 yards). The map itself is 35,000 yards so that means there are 2 metres unaccounted for on each side of the map. It may be a small amount but that means that in the example in the figure above, the squares S.25.b and S.25.d are encroaching on S.25.a and S.25.c of the original “Squared Map”. That proves beyond a doubt that part of squares 28.S.25.a and 28.S.25.c are on the Sheet 28 map. Those that claim that the “a” and “c” squares never existed have apparently not gone through the process that details the evolution of the ”Squared Maps” to the “Revised Squaring Maps”.
On all the maps, whether in yards or metres, you will see that all four corners are marked with the distances north or south and east or west of some location. It was necessary to find out the reference point of each of these locations. To examine the possible origin of these marks, I used the example of the map that showed the area at the southwest corner of Lake Dickebush, south of Ypres Belgium. I chose this location as it was one of the oldest trench maps that were available on the Imperial War Museum DVD collection.
It is important to note that when you are using Google Earth you are relying on the Prime Meridian in Greenwich, England. The marks on the trench maps that indicate that they are “x” east or west of a fixed origin, are not based on the British prime meridian, rather a position on continental Europe.
Using Google Earth we made the approximation that this area, at the lower left corner of the map would be at or near 50.8142N 2.8186E. This was not intended to be exact, rather to have a reference point that we could then use to find the origin.
Not being familiar with the Belgian maps, I thought there may be a clue to this on the left hand border where it has both forms of longitude and latitude codes as 50 deg 50 min and the 56G 48?
A “call out” to our friends in France and Belgium quickly brought the answer! CEFSG Member Alain Dubois Choulik from Valenciennes, France knew right away they were “Gradients” or “Gons”. That led us quickly to an on-line calculator to convert between degrees and gons:
Using that converter we could then convert the reading 50G4608 and arrive at the location on the southwest corner of Lake Dickebush. The point shown as 50G4608 is equal to 50.8147 degrees which is a GPS reading of 50o 48’ 52.92” (a little less than the 50o 50’ marked in the map border).
The next question was “Where exactly is the Prime Meridian for these maps at the Vertical (Longitude) Origin (ZERO)?” Additional experimentation with Google Earth and we had the line of origin as it passes through both the Brussels Parliament Buildings and the Justice Palace. The Brussel’s Planetarium (based on the use of the Planetarium at Greenwich), the first thought, was close but not exact.
Later research into the same question in France would tell us that the French Prime Meridian is at the seat of the National Assembly in Paris, France. The Palace Bourbon, is at 126 Rue de l'Université, 75007 Paris, France (48°51'39.37"N 2°19'1.20"E).
Any references on the maps of Belgium and France appear to be based on “X” metres (or in some cases yards) west of this prime meridian.
The remaining question now was “Where exactly is the Base Line for these maps at the Horizontal (Latitude) Origin (ZERO)?” From checking all the maps and when they split between NORTH and SOUTH it is in the vicinity of top of 36c.S.14 and the bottom of the adjoining square 36.c.S.8 where it becomes 0.00 N=S. Maps 36b and 36c show their lower corner measurements from the origin as 3,019 yards and Maps 44 and 45 switch over to 2,760 metres. If you were not paying attention, who would have noticed they switched for yards to metres between the 30 and 40 series maps? They are apparently the same location as 2,760 metres is 3018.4 metres - so close enough. The same applies on the vertical border between maps 36c and 44 as it switches from the longitude being 91,861 yards to 84,000 metres which are basically equal; It suggests the 40 series maps were made first when they stayed Metric and then when they moved into the 30 series in France they switched to Imperial.
From a review of the maps we can determine that the ZERO ORIGIN of the Latitude is between the 17,240 metres north mark on the upper corners (of any of the maps 36b, 36c, 44 or 45) and the lower corners at 2,760 metres south. The sum of those two numbers is the 20,000 metres that make up each metric map. The total map is 22,000 yards (20,116.8 metres) so we know that the blank space on the top and bottom of each map is 58.4 metres (63.9 yards). The map is divided into 22 squares in any vertical column, so we can calculate that each mark (20 marks per rectangle a-c or b-d) is 45.72 metres. To find the ZERO then we must go up 60.37 marks from the bottom of any map (2760 m/45.72=60.37). That is close enough to 3 squares up so that a line that runs through any map X.11.c.0.0 on the right or S.8.c.0.0 on the left is the ZERO ORIGIN (i.e. a line from 36b.S.8.c.0.0 to 45.X.11.c.0.0).
Relying once again on Google Earth we can see where this line is drawn by marking all the ZERO ORIGIN coordinates for maps 36b, 36c, 44 and 45:
At present, I do not know if we have found the relevance of this line (location) but it appears to be at the "Baie d'Authie" which is in the Somme Region of France.
The Last Step – Using the Trench Map
So as not to presume that everyone has used a trench map to find a location, here is a simple example. In my case, I have my grandfather’s original trench maps for the area north of Arras and south of Vimy, known as the Roclincourt sector.
The next step in the process is to look at the details of the map and in the specific areas we are looking at in this example, which has been selected as Thelus Woods in sector A6.
In the early sections of this article we have described how the Main Sectors (Large Alpha Codes) have a variation in the number of squares. In this particular example, we are dealing with Sector “A” so it is missing the top row, which would decrease it from 36 to 30 squares, but it is also missing one-half of all the left squares. The end result is that “A” has 25 squares 1,000 yards by 1,000 yards plus the 5 rectangles on the left that are approximately 500 yards on the horizontal by 1,000 yards on the vertical.
It is important to note that in the case of a composite map you may have two or more maps put together so you must be careful to identify the main map and sector identifiers before looking at the alphanumeric squares. The earlier image of the Bethune Map is a good example.
Once you have moved to SQUARE A you will see the sub-squares (except for the left rectangles) are divided into 4 quadrants, labelled as a, b, c, and d starting in the upper left corner. For this example, the 51bNW trench map from the McMaster Collection has been used, as these quadrants are already marked.
If you want to measure the distance between points or time or travel reported in the war diaries, then the following basic information may be of assistance:
  • The large squares, such as that identified as A6 in this example is 1,000 yards by 1,000 yards.
  • Each of the large squares has 4 quadrants in a 2 x 2 layout, such as A6a, A6b, A6c and A6d each of which therefore measure 500 yards by 500 yards each.
  • For precise measurement, particularly to identify enemy emplacements or to set artillery fire, each of the quadrant squares were further sub-divided into 100 smaller squares, thus each was 50 yards by 50 yards. These are not identified on the maps by letters or numbers but rather by the hash marks on the 500 yard squares. For these hash marks you read from the left to the right on the bottom of the square first and then from the bottom of the square upward.
Thelus Woods is located at 51b A6 d.5.1 which says the following:
  • on map 51b
  • in the sector A6, an area 1,000 yards by 1,000 yards
  • in the lower right quadrant d, an area 500 yards by 500 yards
  • the centre of which is at about 5.1 being 5 marks (250 yards) across and 1 mark (50 yards) up.
If you want to see where this is on Google Earth, use the Great War British Trench Map Coordinates Converter, as previously discussed. As well as providing an image, it gives you the actual GPS coordinates (50.3568, 2.8065) which you can enter in Google Earth.
If you have any questions or comments on this review article, please send them to:
Richard Laughton, LMC Great War Research Company
Milton ON Canada L9T 4N8

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Phil Evans

Richard,

I cannot get the PDF to download at the moment.

Phil

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keithfazzani

Nor can I, presumably a techie problem

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4thGordons

I couldn't get it to download either - but I took the liberty of copying the full post and creating a pdf which is small enough to link here.

If Richard approves I can easily do so but didn't want to without his OK

I think it is a very useful piece and made some things clear to me which I did not previously understand!

Chris

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Martin Feledziak

A very interesting subject and I do not wish to de-rail it by posting this very slightly off topic post in the middle of your good work but it does relate to map co-ordinates and much the same maps you are using.

It relates to the re-location of Captain KILBY VC from where he was originally buried alongside the canal during the opening days of the battle of Loos and where he, and others in his assault party, remained for 14 years.

In 1929 he was moved to Arras Road Cemetery.

Looking at the concentration Burial return the original map ref appears correct taking into account that they were using the 36C map - ( 44a.A.16.c.60.55. )

but the handwritten co ordinates for the re-burial ( 51b.A.16.b.85.20 ) appear to be part way between Arras Road Cemetery and Nine Elms Cemetery.

So slightly out by 300 yards or so.

I do not know if this information helps to confirm your current findings.

post-103138-0-85475100-1456912455_thumb.

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laughton

Martin:

I have copied your post over to:

http://1914-1918.invisionzone.com/forums/index.php?showtopic=236938

If we try to deal with it here I will lose my GET SQUARED! topic.

Our group has done a lot of work in that area and I will pull the files and be back at the new topic area in a moment.

Richard

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laughton

There is a server problem on our MediaFire site - sorry for that! I have changed the link so it downloads directly from my web site.



You can find it (GET SQUARED!) here from my personal web site:



http://laughton.ca/d...ts/ww1/pub9.pdf



I changed the link in the first post to go to that site as well.



Apologies for the technical error but we do not control MediaFire.


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Old Tom

May I air a question that has intrigued me since I read Dr. Peter Chasseau,'s book years ago. In 1914 the French had adopted a decimal system of map references and yet the Brits devised the system that Laughton has commendably set out. Why?

Old Tom

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laughton

Knotty John:

Thanks so much for posting those links. The information contained within was of considerable assistance, however it will take time to digest it all! I found it interesting that the 1918 text referred to "computers" but it appears the 1918 computer was a person not a machine.

Of importance, it states that the Royal Observatory of Belgium is the source of the Prime Meridian of Belgium. That facility is in the south of Brussels about 490 metres east of where I had placed the line. It has GPS coordinates of 50°47'53.99"N 4°21'29.99"E. The document says (Part II page 59 of 117 - page 142) that the Observatory is 4°22'12.70"E of Greenwich but on Google Earth that is 830 metres too far east. They do refer to the issues with the "triangulation" process used at that time. I must move into the next phase of understanding the Bonne Projections.

The report also refers to AMIENS as the French origin of Latitude, but that can not be the ZERO ORIGIN of the maps in yards or metres as it is 55 kilometres to the south. More reading and investigation is required. The term "Origin of Latitude" apparently differs from the ZERO ORIGIN as on the page (142) referenced above it says it is at 50°24'0.00"N which is not too far off where it was measured off the trench map at 50°23'0.50"N (about 250 metres). I used the on-line trench map converter to arrive at those locations so it is more accurate than I expected.

Richard

(from my origin: 43°30'1.96"N 79°52'26.32"W)

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Knotty

Hi Richard

Glad you found the link useful, and they are helping your research.

Many moons ago when I started my career, the nuances of myriads of projections were the bane of my life, they still were when I retired even though modern technologies, the good old desktop PCs, helped out. I am sure that fellow surveyors/ cartographers will echo the same sentiments.

I still have some of my old books I can call on for explanations, so if I can help feel free to PM.

John

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Old Tom

Knotty,

Many thanks for that steer. A fascinating, albeit somewhat complex document. I have yet to study the section on map references but it does seem to provide an answer to my question. Which I guess is more complicated than 'the Gunners insisted on yards'. If anyone else is interested the part of the report is Appx III Page 159.

Old Tom

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SapperBoo

Knotty John:

Thanks so much for posting those links. The information contained within was of considerable assistance, however it will take time to digest it all! I found it interesting that the 1918 text referred to "computers" but it appears the 1918 computer was a person not a machine.

Of importance, it states that the Royal Observatory of Belgium is the source of the Prime Meridian of Belgium. That facility is in the south of Brussels about 490 metres east of where I had placed the line. It has GPS coordinates of 50°47'53.99"N 4°21'29.99"E. The document says (Part II page 59 of 117 - page 142) that the Observatory is 4°22'12.70"E of Greenwich but on Google Earth that is 830 metres too far east. They do refer to the issues with the "triangulation" process used at that time. I must move into the next phase of understanding the Bonne Projections.

The report also refers to AMIENS as the French origin of Latitude, but that can not be the ZERO ORIGIN of the maps in yards or metres as it is 55 kilometres to the south. More reading and investigation is required. The term "Origin of Latitude" apparently differs from the ZERO ORIGIN as on the page (142) referenced above it says it is at 50°24'0.00"N which is not too far off where it was measured off the trench map at 50°23'0.50"N (about 250 metres). I used the on-line trench map converter to arrive at those locations so it is more accurate than I expected.

Richard

(from my origin: 43°30'1.96"N 79°52'26.32"W)

"The Greenwich Meridian was chosen as the Prime Meridian of the World in 1884. Forty-one delegates from 25 nations met in Washington DC for the International Meridian Conference. By the end of the conference, Greenwich had won the prize of Longitude 0º by a vote of 22 to 1 against (San Domingo), with 2 abstentions (France and Brazil)." http://www.rmg.co.uk/discover/explore/prime-meridian-greenwich

"Both the positions recorded by Mugnier as 50°25'0.0006", 4°22'12.6978" and Winterbotham (see also Close:1919zr) as 51°10'06.895", 4°22'05.89" are both a few kilometers off. After a bit of help from the Nationaal Geografisch Instituut and the original triangulation of Belgium [#institut1867triangulation], the actual origin of the map as 50°24', which give results that are reasonable."http://rdf.muninn-project.org/ontologies/btmaps.html#TrenchMap10

The 'geodetic problem' is how accurate was the survey that decided the position of the "old Brussels observatory". The accuracy of this fix was of no significance to trench map users; it was a problem for Winterbotham who was trying to reconcile differences between meridian's used by Belgian and French map makers. It also becomes an issue for those people (most of us) who want to use GPS. If you are keen to find a mathematical solution I would use 4°22'5.89 as suggested by IGN Belgium (there equivalent to Ordnance Survey) in the muninn link.http://rdf.muninn-project.org/ontologies/btmaps.html#TrenchMap10

However. "The true prime meridian of the world, as agreed by every nation on the planet in 1984, is the IERS Reference Meridian, which is also known as the International Reference Meridian or IRM."http://www.rmg.co.uk/discover/explore/prime-meridian-greenwich

The difference between the 1914/1918 Prime Meridian and the 1984 Prime Meridian is 102.5m at Greenwich (bigger at the Equator). I assume the IGN value (4°22'5.89) has taken account the new definition of ZERO and any surveying errors in the .

I hope this helps.

SapperBoo

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trajan

As an aside. Here in Turkey many of the earlier antiquarians located sites by L&L, and so I still teach my surveying students this method. Of course, GPS makes it easier to relate it to UTM systems, but I have found in this country at least that when converting to UTM references, there is, shall we say, an imposed error of up to 100 m. west-east.

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WhiteStarLine

Richard, thanks for sharing a very detailed body of work. I did the same exercise in 2012 from first principles and am impressed with your approach.

For those trying to reconcile modern coordinates with the meridian of Greenwich, don't forget that the WGS84 model averages out a world-wide set of results to define the WGS84 prime meridian - roughly analogous to many atomic clocks averaged out to give UTC. When we toured France in 2012, I carried a GPS datalogger with me. When we visited Greenwich and stood over the famous prime meridian, the GPS logger put me as in the same latitude but ~ 200 m away for longitude. This is consistent with the underpinning model.

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Old Tom

Having read and partially understood some of the information present above I feel a need to, as lecturer said to a group including me years ago, 'rehearse my faith' and request that those who know better will let me know if it is nonsense.

I suppose there may be a difference between a surveyors and users appreciation of a map. My rather simplistic understanding as a user is that the main function of a map is to allow the position of locations in relation to one another to be measured. In other words location 'a' is 2,500 yds NW of location 'b', or in terms of gunnery the range and bearing of a target. The surveyor, it appears, seeks to establish locations in absolute terms. This leads to the difference described in post 15.

Again my understanding of early surveys like that of the UK by OS were based on a selected base line of accurately measured length and triangulation. Hence when two adjacent surveys such as France and Belgium both cover a border area there will be differences as the surveys were made from different base lines. I assume that in the WW1 era such clashes were inevitable.

Old Tom

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Knotty

Old Tom

You've hit the nail on the head with your analogy. It's very easy to get bogged down in the scientific aspects of mapping, let the surveyors & cartographers produce the final product,in this case the map,and users do just that,use it!

John

(As a retired surveyor,I await the flak from those still practising)

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WhiteStarLine

Hi Old Tom,you are of course absolutely correct, as is John. The ultimate aim of the WW1 cartographer was to produce a product of such accuracy that would allow, as an example, a WW1 gunner to fire on a reported enemy position using predicted fire. In other words, if an observer saw a target on the cross roads, an artillery position many kilometres away could use the map with such confidence that first rounds would land on that position. Post-war analysis revealed how successful this really was.

The aim of modern enthusiasts such as Richard, Rob and others, is to come up with a body of work that enables a modern user to research a WW1 location from a WW1 trench map and stand on the same spot using modern techniques such as Google maps and GPS. We did this in 2012, following my grandfather's brigade's footsteps.

For those developing techniques to do this,concepts such as the exact contemporary and historic position of the Greenwich longitude, Paris meridian and its Belgian counterpart are part of this research. Once again my thanks to Richard, Rob and others who have published in this field.

Cheers,

Bill

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momsirish

I downloaded your PDF very easily but cannot seem to transfer it to an external drive where I have more space. Thanks for sharing it I hope to some day to use it to locate the trench coordinates where a relative was buried nearby.

thanks

momsirish

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Howard

Most of the problems highlighted here are covered in Col. Jack's excellent Report on Survey of the Western Front. For an official report, it is surprisingly readable. He outlines the expected accuracy of British maps, both for absolute and relative positions. Absolute positions were more of interest to surveyors & cartographers, relative positions being key to artillery, but modern users who want to identify specific points with a GPS need good absolute accuracy. Sadly, that is more difficult than it looks.

Two versions of the report are available here, one as scanned and one processed using OCR to give editable text. The OCR accuracy and the old use of I for 1, O for 0 etc. means there are some errors in the modern text version but that does allow for searching etc.

It may be useful to remind non-surveyors that a single point on a map or on earth will have quite a number of lat/long values depending on its origin etc. I think many people will expect that a lat/long value, when put into a GPS with identify just that place. This is very far from being true and is a major nuisance when trying to locate places using historic data.

Howard

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Bernoullis

Richard, that is an impressive piece of work, and thank you for sharing it. Great to see your Grandfather's Roclincourt trench map coming to the fore again!

(And thanks again for your help here a couple of years back. :thumbsup: )

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laughton

Some time later while trying to solve the French Trench Map coordinates, I came across this table that gives the location of all Prime Meridians:

http://web.archive.org/web/20110726052102/http://www.kb.nl/skd/mathemat.html

 

This may help us in the future!

 

LOCATION OF PRIME MERIDIANS

City Country Position
Alexandria Egypt Used by Albert Hermann in 1930 for a reconstruction of a map of Marinus of Tyrus. The meridians are hours west or east of Alexandria
Amersfoort Netherlands E   005º23´
Amsterdam Netherlands E   004º53´01"
Antwerp Belgium E   004º22´50"
Athens Greece E   023º42´59"
Batavia (Jakarta) Indonesia E   106º48´28"
Berlin Germany E   013º23´55"
Berne Switzerland E   007º26´22"
Bogota Colombia W   074º04´53"
Bombay India E   072º48´55"
Brussels Belgium E   004º22´06"
Bucharest Romania E   026º07´
Cádiz Spain W   006º17´42"
Canberra Australia E   149º08´
Capetown South-Africa E   018º28´41"
Caracas Venezuela W   066º55´50"
Celebes, Middle Meridian of Indonesia E   121º48´
Christiana (Oslo) Norway E   010º43´23"
Copenhagen Denmark E   012º34´40"
Córdoba Argentina W   064º12´03"
Ferro Canary Islands W   017º39´46"
Greenwich United Kingdom       E   000º00´00"
Genoa Italy E   008º55´
Helsinki Finland E   024º57´17"
Istanbul Turkey E   028º58´50"
Jakarta Indonesia See: Batavia
Julianehaab Greenland W   046º02´22"
Kaliningrad Russia See: Köningsberg
Köningsberg Russia E   020º29´47"
Leningrad Russia See: St. Petersburg
Lissabon Portugal W   009º11´10"
London United Kingdom W   000º05´43"
Madras India E   080º14´50"
Madrid Spain W   003º41´15"
Mexico City Mexico W   099º11´40"
Moscow Russia E   037º34´15"
Munich Germany E   011º36´32"
Naples Italy E   014º15´42"
New York City (Manhattan) United States W   074º00´29"
Oldenburg Germany O   008º12´
Oslo Norway See: Christiana
Padang, Sumatra Indonesia E   100º22´01"
Paris France E   002º20´14"
Peking China E   116º28´10"
Philadelphia United States W   075º08´55"
Pulkovo (St. Petersburg) Russia E   030º19´39"
Quito Ecuador W   070º30´
Rio de Janeiro Brazil W   043º01´21"
Rome Italy E   012º29´05"
Rotterdam Netherlands E   004º29´46"
San Fernando Spain W   006º12´
San Francisco United States W   122º27´
Santiago Chile W   070º41´00"
Singkawang, Borneo Indonesia E   108º59´41"
South Sumatra, Middle Meridian of       Indonesia E   103º33´
St. Petersburg Russia E   030º18´59"
Stockholm Sweden E   018º03´30"
Sucre Bolivia W   065º15´
Sydney Australia E   151º12´23"
Tenerife Canary Islands W   016º35´
Tirana Albania E   019º46´45"
Tokyo Japan E   139º44´40"
Washington (D.C.) United States W   077º00´34"

When not taking into account which prime meridian is used the following situation might occur.

HUMOR: Teaching Coordinates

The geography teacher was lecturing on map reading. After explaining about latitude, longitude, degrees, minutes, and seconds, the teacher asked, "Suppose I asked you to meet me for lunch at 23 degrees, 4 minutes, 30 seconds north latitude and 45 degrees, 15 minutes, zero seconds east longitude."

After a confused silence, a voice volunteered, "I guess you'd be eating alone."

(Ken Everard, on Maphist, 8 February 2001)

When the teacher meant GMT as prime meridian he would have been lunching somewhere in the Arabian Desert called Dawasir. Had the teacher meant e.g. the San Francisco prime meridian he would have been lunching on a boat on the Great Bahama Bank near Channel Rock!

 

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