Finetuning inexact coordinates fitting to OSM

Question

Dear All,

I scanned an old map and georeferenced it with Qgis (gdal).The result is ok - nearly. When I compare in QMapshack the grids UTM32 - printed grid on the scan and the QSM Grid - they are a little bit different, maybe 50 m in X Y. The geotiff is inexact - I checked it. My question is if I can finetune the geotif coordinates so that the are exactly congruent to OSM-Grid ?

Here's the output from gdalinfo:

gdalinfo wanderkarte_MK_54.tif 
Driver: GTiff/GeoTIFF
Files: wanderkarte_MK_54.tif
Size is 8630, 3774
Coordinate System is:
GEOGCS["WGS 84",
    DATUM["WGS_1984",
        SPHEROID["WGS 84",6378137,298.257223563,
            AUTHORITY["EPSG","7030"]],
        AUTHORITY["EPSG","6326"]],
    PRIMEM["Greenwich",0],
    UNIT["degree",0.0174532925199433],
    AUTHORITY["EPSG","4326"]]
Origin = (7.611058772101766,51.326286037305387)
Pixel Size = (0.000040664445937,-0.000040664445937)
Metadata:
  AREA_OR_POINT=Area
Image Structure Metadata:
  INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left  (   7.6110588,  51.3262860) (  7d36'39.81"E, 51d19'34.63"N)
Lower Left  (   7.6110588,  51.1728184) (  7d36'39.81"E, 51d10'22.15"N)
Upper Right (   7.9619929,  51.3262860) (  7d57'43.17"E, 51d19'34.63"N)
Lower Right (   7.9619929,  51.1728184) (  7d57'43.17"E, 51d10'22.15"N)
Center      (   7.7865259,  51.2495522) (  7d47'11.49"E, 51d14'58.39"N)
Band 1 Block=8630x1 Type=Byte, ColorInterp=Red
  Mask Flags: PER_DATASET ALPHA 
Band 2 Block=8630x1 Type=Byte, ColorInterp=Green
  Mask Flags: PER_DATASET ALPHA 
Band 3 Block=8630x1 Type=Byte, ColorInterp=Blue
  Mask Flags: PER_DATASET ALPHA 
Band 4 Block=8630x1 Type=Byte, ColorInterp=Alpha

Kind regards

Rawbit

Accepted Answer

3

So if I understand you correctly, the problem is simply that the georeferencing didn't work as well as you would have expected. (This is not an OpenStreetMap specific question really and should have been asked in a more general GIS forum.) This is normal; the quality of the result depends on the quality of your scan, which algorithm you choose, how many GCPs you set, and how precise you are in setting them.

If you believe that simply shifting the GeoTIFF will help, then the easiest option is to use gdal_edit.py to override the geographic bounds of the image.

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answered 30 Oct '15, 23:24

Frederik Ramm ♦
82.5k●92●720●1273
accept rate: 23%

2

Hi,

thank you so much, gdal_edit is exactly what I'm looking for ! I used gdal_edit.py -a_ullr 7.610300 51.326280 7.961292 51.172818 testmod.tif

Kind regards

Rawbit

(31 Oct '15, 09:18) Rawbit

Finetuning inexact coordinates fitting to OSM

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