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Map overlay request


TEW
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I've spent too long already trying to do a map overlay and not arrived at anything satisfactory.

I have the attached plan of medical posts & routes that has no map squares, only posts C4 & C5 have map references given, I've added one for A6. The RAPs C6, 7, 8 & 9 need locating to a map ref which I can plot onto other maps.

Not sure if the plan is a from tracing or a sketch by eye.

C4 & C5 are split across two maps but Macmaster have a nice composite map.

Thanks in advance. 

TEW

http://digitalarchive.mcmaster.ca/islandora/object/macrepo%3A69483/-/collection

Overlay.jpg.9c361aebdb016c6a447fc335e1d6fda3.jpg

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@TEW, were you looking for an overlay over a modern map or over the composite trench map (or both)?

Large sketch maps are not easy, unless they are of survey quality.  This one is 8 x 18 km and I would not interpolate from it.  It has the 8km axis of la Boisselle to le Sars pretty well spot on but it places Miraumont and Grandcourt some 800 metres north.  While it is easy to rubber sheet these two into the correct position, it give the overall map a skewed appearance that I tend to avoid.  I skewed it a trifle and I'm not happy with how it looks.  Pins 4 and 5 are Pys and Grandcourt on the modern map. 

Alternatively,  you have supplied 3 Great War references.  Supply a larger extract for Courcelette grid and one more reference and we can do a direct entry for these 4 references at mapcrop.tmapper.com.  This will provide a better fit and will take under 2 minutes to produce.

The final map, with opacity slider, lat, lon position, distance / bearing and baselayer selection is at http://mapcrop.tmapper.com/georef.html?id=kyaseq81.  However, I wouldn't use if for anything better than "in the vicinity of".

image.png.ba09790f2f7f069d620bb21b6898d5f9.png

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Many thanks. PM sent

TEW

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Here is a significantly better correlation thanks to the known points you sent.  The evacuation routes follow the known roads and the Thiepval / Authille / Ovillers / Pozieres fits nicely.  Outside this area does not correlate, suggesting a hand-drawn or roughly traced map.  Beaucourt is good and Miraumont is OK but Grandcourt is way off.

The whole overlay is at http://mapcrop.tmapper.com/georef.html?id=kyctwz1w and here is an enlargement with a high degree of transparency just to show the correlation between evacuation routes and known roads.  If you overdo the zoom, (eg B5 and the Pozieres civilian cemetery), you can see that this is not a survey but a good field sketch.

image.png.5ad164554b0dfd47476f8633b3b98a62.png

image.png.c650febf62bfac9d7a21800dd77296dd.png

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Many thanks and glad the extra points helped. I Really must get to grips with tmapper.

Should add an image citation, this one is from TNA WO95/734/2, not available on Ancestry.

TEW

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@TEW Here is the next iteration - a double overlay where the McMaster map has been integrated into the modern Satellite view and the original trace overlayed as per previous posts.  You can click on a point of interest and a modern lat, lon will appear.  For example, here is C8.  Copy and paste this into tMapper's Advanced Users -> Forward Convert option and 50.06196, 2.749153 becomes Sheet 57c.M.19.d.0.4, which looks pretty good.

Discarding conversion errors and any errors I have made in the overlays, I do not believe the original trace is accurate enough for what you want to achieve.  Points C7 and C8 happen to look realistic but the original trace is not survey quality, although pretty impressive for the conditions under which it would have been first made.

As always, the opacity slider will allow you to increase the transparency of the trace to see the trench map underneath.  The double overlay is at http://mapcrop.tmapper.com/georefdouble.html?id=kyctwz1w.

Credits: McMaster University, TNA, tMapper

image.png.85daa63d8b9b8adcc6eeac3b6ef45b9b.png

image.png.7c5c2c44710a1e54d8bc2e62ea11ce58.png

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Thanks, I was looking at this yesterday on a proper monitor and desktop pc and realised that on my android phone I'm not seeing the opacity slider or the main menu option, tried two browsers.

I did the forward converts and had a good while trying things out.

I've also gleaned more information from other diaries EG. the Canadians held this frontage about 5 weeks earlier than the sketch map which I now think is late December 1916. The Canadians also had RAPs in the area of interest.  If the Canadian RAPs plot out as much the same as C6-C9 then I suspect the RAPs didn't move.

In which case we'll see how much error there is in the sketch.

TEW

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