TransDEM Forum

Hi I photographed an old 6 inch OS map (UK) dated in the 1930s as it had a railway I was interested in. I have lots of photographs covering the route of the railway. I am slowly adding them to the DEM map.

Is there any way of moving a loaded raster map about? I have two maps which are slightly missaligned when viewed on the DEM map. I would dearly love to be able to move them into alignment by shifting one of the maps gently north / south or east/ west. Does such a method exist? I was very careful in setting up the cordinates for the raster maps but one of the five is slightly out. Can I adjust the co ordinates in situ or will I be forced to go through the whole process again and hope the maps align this time?

You can edit the .trf file which is plain text. "Punkt0_t" denotes the south-west corner in UTM coordinates. However, most often it's not only the position of the map, scaling and orientation may also contribute to misalignment. Therefore, georeferencing anew might make sense. If your 1930s' map already bears the O/S grid (it was only invented in 1936) you should use it. Otherwise a modern O/S topographic map might help to identify landmarks and obtain their coordinates.

You are aware of the map tile service(s) with historic O/S maps?
http://forum.transdem.de/viewtopic.php?p=493#p493

Hi I have experimented with the trf file and moved the map someway towards alignment. Though it is fiddly and a bit of guess work. Is is possible to rotate the map? Can I suggest that a future enhancement would be a mouse drag-able map.

I live in Northern Ireland and the GB OS website does not cover NI. The local OS want payment for maps of suitable scale. I went to the local city library to find the old maps. I was surprised that they allowed me to photo it ( but not photocopy ) My photos only cover the local area around the railway track and the grid lines are not consistent from one photo to the next. The maps were held in a large ledger so it was difficult to get them flat. Also I manually tried to keep the height I was photographing from consistent. A possible source of error was at the crease of the ledger.

I use Google Earth to get the co ordinates of the references on the map. A few of the road junctions or field edges have changed but there is enough to use. Perhaps in the passing 70 years some of the reference points are not what they were. I can still see the outline of large lengths of the original railway on Google Earth. There is a lot of cloud over parts which is going to make it difficult to work with. Is there another system I could use that still gives me co ordinates to reference my raster maps?

I have experimented with tiles. The wire mesh in Trainz route seems very fine and obscures the detail on the tile. Of course the tile is flat and the land is contoured so it takes a bit of fiddling to move the tile up and down to be able to read the layout on the tile.

That would be too easy.
No, seriously, the TransDEM raster image processing is a complicated matter. It's a combination of an affine transformation for the image itself and a non-linear geo-coordinate transformation for the contents. Simple rotation does not really fit in here, it might give a false sense of security.

Did you have a look at the Ordnance Survey Ireland portal? They cover NI, not to the same detail as the Republic of Ireland, though. However, their coverage includes historic topographic maps of NI. Coordinate system is the newish ITM.
http://forum.transdem.de/viewtopic.php?p=38#p38

I looked at the Ordnance Survey Ireland portal. Unfortunately the historical maps do not display the railways that ended in the 1950s. I looked at SABRE maps - Historical NLS - Barts Ireland. It has the old railway on it. But I do not know what the scale or the co ordinate system is. Or if it would be capable of producing tiles for Trainz. This is very new to me.

I have configured the map tile settings for the two historic maps of Ireland hosted by NLS, see here: http://forum.transdem.de/viewtopic.php?p=835#p835