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I am trying to georeference an old map of the German Reich from 1930's. The map is based on the topographische Übersichtskarte des Deutschen Reiches 1:200000.

The coordinates depicted on the map, that I want to use to georeference it, use the Ferro Meridian. I know that the original map uses a conic projection (German: Schnittkegelprojektion) with two parallels at 50° and 53°. Axis of the cone is the same as the axis of the earth. I don't know anything about the central meridian other than that the angle between the central meridian and the corner/border meridians (German: Randmeridiane, do not exactly know the translation) is 0°23'28''5.

The issue is to find a suitable projection, which fits ok and at the same time allows me to input the coordinates in Ferro using ArcMap as the geoereferencing tool.

Part of the map

  • Do you have projected coordinates or lat-lon values only? If you have projected coordinates, I would georeference the map to those coordinates (leave coordinate system unknown) then use techniques similar to this except define a custom PCS using a ferro-based GCS. – mkennedy Oct 31 '18 at 16:53
  • Also see Cliff Mugnier's article on Germany. – mkennedy Oct 31 '18 at 17:22
  • I uploaded part of the map as I do not really know what you mean by projected coordinates. As you can see I have the lat-lon values. I know in terms of degree, the width and length of grid. – Rara Nov 5 '18 at 9:46
  • The central meridian (ferro-meridian) was changed to Greenwich in 1923 and then was determinate to 17°40' west. On your map, you can find both values i think. So 12° east (Greenwich) corresponds to 30° east (ferro). On your map it looks like the central meridian of the projection is near 32° east (ferro). – Andreas Müller Nov 5 '18 at 10:22
  • some similar overview map landkartenshop.de/product_info.php?products_id=11479, both systems are printet on the map border. – Andreas Müller Nov 5 '18 at 10:30
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See the first two maps. They have both Ferro and Greenwich longitudes directly labeled, so you can determine Greenwich-based control points. I would try 3-5 points left right at both top, middle, and bottom of the map and try directly georeferencing to lat/lon. Note that the longitude lines bifurcate so you'll have to pick the main line.

If that doesn't work well enough, try building a Lambert conformal conic projected coordinate system (PCS) using central meridian = 32° Ferro AKA 14°20' Greenwich and standard parallels about 50° and 53°. Use the Create Fishnet tool to make a 1°x1° graticule and project it to the Lambert PCS. Use that to georeference the map. The original map's graticule is 2' so you might be able to discern 1/3' or 1/4'.

For the datum, about the best you can do is DHDN. It's at least on the same ellipsoid (Bessel 1841).

  • I tried your second version. However, I have trouble to get the Fishnet into the right position. Is there anyway that I can input the lat/lon values as the X and Y coordinates? – Rara Nov 12 '18 at 8:20

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