When I add aerial images from a recent survey (delivered in EPSG:31468, DHDN_3_Degree_Gauss_Zone_4) to a map document, these differ in position from a basemap as can be seen in the screenshot below (about 150m in ~40°). I carried out these steps:
- Set up a new map document
- Set data frame coordinate system to EPSG:31468
- add the aerial image
- add a basemap (here: openstreetmap)
Overlaying it with a parcel dataset from a different source indicates that my aerial image is positioned correctly, so what have I done wrong?
Aerial vs. osm basemap:
Overlay with parcel dataset:
Answer
As determined by PolyGeo this is a transformation issue (http://support.esri.com/technical-article/000002828). Steps to solve this in detail:
Right click Layers, chose properties, 'Coordinate System' tab:
Click 'Transformations...'
Note that at this point no transformation method can be selected.
Under 'Convert from:' select GCS_WGS_1984 and 'Into:' GCS_Deutsches_Hauptdreiecksnetz (applies for this example):
Now a transformation method can be selected:
Click OK. Now the basemap layer matches the aerial image:
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