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Salonika front maps , Datum and projection


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I am a new member from Greece ,

Hello to all the company , 

 

Does anyone know who was datum and projection used by the topographic teams to compile Salonika front maps ?

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Hi Stavros,

Welcome to the forum, I have a trench map CD from the Salonika Campaign Society that contains information about the map creation, I will have a look later today and see if it answers your questions. 

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Hi Stavros,

Datum and projection are not specifically mentioned in the information on British Military map making in the Balkans. If you PM me your email address I will send you a copy of the article from the CD, but before you can use the Personal Message function on the forum you need to make a few posts. A couple of replies to this topic should do the trick.

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Hi Gardenerbill ,

 

I have these cd from Salonika Campaign Society , they really do not mention anywhere about Datum and the cartographic projection of the maps, data absolutely necessary for someone who wants to determine with a very good accuracy, some point of interest on a map making through some special applications the georeferencing process.

 

Nevertheless, thank you very much for your time.

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Stavros raised this with me shortly after purchasing the maps.  I have done quite a bit of reading / researching into this, without success.  Learned quite a bit about mapping - just not helpful to the specific question.

 

I would like to find some method of converting the grid references on WW1 maps (specifically those relating to the "Eastern Front") to modern latitude and longitude.  Starting with (for example) a reference of 117 / 190 as used on one of our maps on the DVD without any additional "leading codes" is not that helpful (so far).

 

Any help appreciated.

 

Keith (SCS Mem Sec)

Edited by Gully Ravine
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Hi all,

 

I've been in discussions with Stavros since August and he sent me some material referenced in the above posts.  There are two approaches to this but first, a big apology to @Stavros.  I totally forgot that a few years back, when I was researching formulae for converting Western Front references to WGS84, my first visit was to the work of Mugnier[1], whose Grids and Datums columns give the history of each country's geodesy from the earliest times to the modern day (1980s).  I only remembered this useful reference series after commencing this post!

 

So the first approach is to find the spheroid of reference, the projection and the point of origin used by the WW1 military surveyors.  I've offered to assist Stavros but I won't be able to help actively until some of my Western Front map tiling has completed.  If someone wants a go, here is an approach that generally works.

 

These days, petroleum or remote sensing is the principle driver of mapping, but in our time of interest, the datum and projection was military-driven, so find what the surveyors used in the country of interest at the time of interest and you probably have an answer.

 

Determine Spheroid of Reference

 

Mugnier quotes:

 

   "In 1889, the Greek Army Geographical Service was formed, and classical triangulation commenced immediately. The agency name was later changed to the Hellenic Military Geographical  Service (HMGS). The initial starting point for the triangulation was the Old Athens Observatory where Fo = 37° 58' 20.1" North, Lo = 23° 42' 58.5" East of Greenwich, and was referenced to the Bessel 1841 ellipsoid where the semi-major axis a = 6,377,397 155 meters and the reciprocal of flattening 1/f = 299.1528128."

 

   "The Greek Military Grid was based on the Hatt Azimuthal Equidistant projection, a system originally presented on the sphere by Guillaumme Postel."

 

The use of the Bessel [2] spheroid of reference isn't far off the reference system used on the Western Front (Carte de France) but their projection (Bonne) was widely different.

 

Determine Map Projection

 

It is a reasonable assumption that the survey notes cited by Stavros relied on the extant projection with French astral fixing used for survey points.  With a bit of luck, this is a good starting approach to find their point of origin.  When converting the Western Front, I found spherical geodesy to be unusable but Snyder's ellipsoidal formulae [3] to be absolutely spot on over a tens of thousands of square kilometres (given a WW1 standard grid had a best case 25 square yard coverage before any margin of error).

 

Snyder's ellipsoidal formula for Micronesia was his implementation of the Hatt projection and would be a good starting point for distances below 800 km.

 

image.png.7957cd07f3ba3eb7b0125ffdd45d01e9.png

Determine Point of Origin

  1. I would start off by finding the places cited by Wood [5].  Particularly Vardar Plain and the White Tower, Salonika.  Use this to determine a point of origin.
  2. Record this origin in WGS94 latitude and longitude as the center of projection and origin.
  3. Find a length between the origin and a known point in 1916 metres (x and y, measured from WW1 map in Bessel CRS) using the grid coordinates of the trench map.
  4. For simplicity, use Snyder's inverse spherical formulae and the Bessel sphere.  Your results should look very roughly OK but nothing like the accuracy you want.
  5. To see if you have really made it work, try the inverse ellipsoidal formula.  These take me well over an hour to setup correctly (noting carefully any arctan assumptions to save much grief!).
  6. Do a few and you will spot a pattern - the linear translation you need to make it all align on a WGS84 grid.  Technically this is a Molodensky transformation, but I never bothered with a 7 parameter one over the distances we are looking at.  Factor this into each conversion.  If you are right, then you get an accurate conversion over considerable distances.

There is a much simpler method and I will leave that to the next post.

 

References

 

[1] Clifford Mugnier, The Hellenic Republic, part of Grids and Datums series, 2002 Louisiana State University, 

[2] F. Bessel The calculation of longitude and latitude from geodesic measurements, Konigsberg Observatory, originally published: October 1825

[3] John Snyder, Map Projections - a Working Manual 1987,  See p 210 for "Clarke's best formula" of 1971 and p 337 for a worked example.

[4] EPSG ESRI:54032 World Azimuthal Equidistant

[5] "The British Triangulation in Macedonia 1916 – 1918".  By Lt Col H Wood, R.E. 15 November 1918

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8 hours ago, Gully Ravine said:

some method of converting the grid references on WW1 maps (specifically those relating to the "Eastern Front") to modern latitude and longitude

 

The simplest method is to take a small section with known points and fit it over a modern map.  Then you have different base map layers (like Streets or Aerial Photos), Distance & Bearing and opacity sliders to help you.  Navigate with pan and zoom.  This example had a 150 year old tree and well that Stavros was interested in.  In the modern map it is very visible, close to the modern road.  You can see the entire image at GeoRef and while this site is currently aimed at Western Front maps, only a few modifications were needed for it to be just as effective for other theatres.

 

image.png.b0f0bc45568203b9292e8c27876ba4c9.png

 

image.png.f01ef82346f89210dad78e0b71cf893d.png

 

This approach is used by National Library of Scotland and some commercial products for the Western Front.  It requires no mathematics, just patience and enthusiasm.  I've just georeferenced and tiled 20 trench maps for Flanders, each of 8 km x 5 km.  If the copyright owners (SKS?) upload 1 or 2 trench maps I am happy to experiment by georefencing, tiling and returning the maps as tiled overlays suitable for hosting with modern online maps such as Google or Bing.

 

If they are not prepared to do this, an alternative appears below, with a caveat that there is a real learning curve.

 

Kavak (click to enlarge)

 

image.png.d2d949ae598a015d8de2922256c3ecfe.png

 

Alternative Approach

 

Note that this approach works well for France / Flanders where many towns, railways, church spires and rivers are in exactly the same place they were in 1916.

  1. Download a suitable product.  I use the Open Source product QGIS  The free or paid version of MapTiler is highly regarded.
  2. Respecting copyright, find a trench map or trench map extract.
  3. Create a new project and add Open Street Map tiles.
  4. Find the location (or insert the Open Street Map search plugin and find it).  Open Street Map is good with modern spelling but these may not relate to WW1 place name spelling.
  5. If you have a complete trench map, trim the margins.  This makes it easy to follow roads and rivers so they don't 'disappear' under the map margin.
  6. Use the Raster Georeferencer and open the trench map.
  7. For an entire trench map, this might test your patience!  Find around 6 points common to each and click on the trench map location then the modern map.  Close to each corner is best.
  8. Click the georeference wizard and don't overstretch the precision or you get some weird looking fits.
  9. Zoom in, pan around and use the opacity slider to reveal modern and WW1 location.

 

Options

  1. Optionally convert into what are called XYZ tiles, used in modern mapping products like Google and Bing.
  2. Save these to your local hard drive.
  3. Ask QGIS to add a Map Viewer
  4. You are now ready for a field trip with a complete georeferenced map and an HTML page to run it.
  5. You can even add Location Services so your table, phone or PC shows you where you are on the modern or trench map.

 

 

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Very useful the information you have written Bill ,
Also valuable, extremely simple and easy tool : http://georef.tmapper.com/

But the problem lies at this point: on some map sheets, there are no fixed points from the time the maps were written until today, because they have faded, changed dramatically, or even disappeared.
That is why I am doing research to find out these valuable elements ( Datum and projection ), but also the mathematical relations, which connect the Cartesian - orthogonal coordinates that all the sexes of the series have, with the geographical coordinates ( N , E ) so that in the first year this conversion is done first, and then the conversion datum and projection . and all this with the aim of maximum accuracy.

There are applications that with a few clicks, give you the ability to geo-report too many maps, with very good accuracy, and very little time (as long as one knows the Datum and the projection )
There is also the possibility for someone to create '' user datum ''  as long as you know the permutation parameters ( DX, DY, DZ , DA , DF )
Bill has already mentioned an application that does all this and I have heard a lot of good Cretans ( QGIS )
I use the application https://www.the-thorns.org.uk/mapping/ and I am quite satisfied.

Today, looking in my file, I noticed that I have a 20K map gender. by the Hellenic Geographical Service of the Army, which has been reproduced with the background of its respective sheet Armee d' Orient.
The important difference is that the Hellenic Geographical Service of the Army, while it has for the same area all the data as shown by its map Armee d' Orient the coordinates at the top of the map, are geographical and not rectangular, this to have I think that the Greek side had received all the necessary information that was written above the allied army, so that with the same background the old observatory of Athens has a starting point (I attach the relevant)

So within the next week, I thought of sending a request to the Hellenic Geographical Service of the Army, lest this valuable information be leaked, and we can go one step further.

Screen Shot 10-24-20 at 04.58 PM.PNG

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Screen Shot 10-24-20 at 05.23 PM.PNG

 

Screen Shot 10-24-20 at 04.59 PM.PNG

Screen Shot 10-24-20 at 05.46 PM.PNG

Edited by Stavros
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  • 2 weeks later...

Unfortunately, the answer I received from the competent military service was negative, and this is because during World War II the Germans took all the relevant files and equipment, which were in the service.

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What a shame Stavros.  At least you tried and we can rule out that approach.

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Hi Stavros,

 

Yes, that report is the holy grail for conversions in northern France / Flanders and it is the basis for Western Front mapping.  It gives the coordinate reference system, survey points, datum and how these were arrived at.  It is an essential read for anyone interested in WW1 mapping.

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Holger Kotthaus
On 24/10/2020 at 16:18, Stavros said:

Also valuable, extremely simple and easy tool : http://georef.tmapper.com/

I use the application https://www.the-thorns.org.uk/mapping/ and I am quite satisfied.

 

Hello Stavros,

 

many thanks for this helpfull references!

 

Cheers Holger

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