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I have bought a few (30) GeoTiff maps from my country's Geo-department - South Africa. They all have a date in the filename and the newest one was created in 2004, I see one is dated 1977 - that old! Anyway, they came with a .tfw file each. When I simply copy these into Google Earth, or use MapTiler to create a default-settings WSG84 tile set, the map is unaligned. Meaning that they are really close to their correct positions but a bit off center and the deviation from supposed-position differs everywhere on the image/map.

Either the maps are wrongly geo-tagged or I use the wrong formats. Please note: I have no clue or experience with maps and their types (WSG84/UTM etc) I need to convert these maps into tiles for my iPhone app.

I have also tried using maps of USA and they worked and were outputted perfectly.

All I can tell about these maps which may help pro's is:

  • It is a big white block with the map inside and the key/legend on the sides/bottom.
  • The map inside has an arced top and bottom and sides/longitude-lines are skew.

I would like to think it is the same as this image: (Only a small part thereof of coarse!) Random earth image

I have tried to realign/resize the map as an image-overlay on Google Earth, but then had no idea of how to output it or get the needed (and corrected) data from it.

If anybody know how to use these, convert them to tiles or tips/tutorials that could help me fix this and get the maps straight, please tell!

If possible I would prefer to do it in MapTiler or at least on a Windows OS machine

Thank you!

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geotiff contains projection information in the header of the actual image file (tif, tiff). The tfw is not needed in most software. I don't know how to accomplish what you want without using an actual gis software to insert and compare with other data (ussually vector) with a known projection. –  Brad Nesom Jun 24 '11 at 15:37
    
Depending on the scale, they may be in south-orientated transverse Mercator on the Cape (older) or Hartbeesthoek datums. The grid system has positive axes south and west and is divided into 2 degree wide zones starting with central meridian 17E. If they're showing up correctly oriented, maybe they're in a EN version. How far off? Could it be Cape vs WGS84? –  mkennedy Jun 24 '11 at 21:39
    
As a matter of interest what project system is reported when you do a gdalinfo request on the tiffs –  nmtoken yesterday
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2 Answers

I would follow up with the people you bought them from, and confirm what coordinate system/projection they are in. They may not be WSG84 at all. It's likely if they are older that they are a NAD27 or other datum that will need to be reprojected.

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The maps were probably hand drawn, then later scanned and may not exactly match the intended projection system. You best bet is probably to georectify the images against known locations and use those georectified images in your application.

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