[Proj] Problem overlaying georeferenced images in Google, Maps(projection problem!)

Jorge jorge.arevalo at gmail.com
Fri May 30 07:12:20 EDT 2008

Now, the results in Google Earth:

The image before reproyecting (UTM zone 30 datum ED50)

The image reproyected

What's the problem?:
- The input image's projection really isn't UTM ED50 (Mapinfo lies??), or is bad georeferenced (low probability...)
- The output image's projection really isn't GMaps projection (assuming GMaps projection = GEarth projection)
- GMaps projection not equal GEarth projection (I think so...)
- Any other?

The line executed:
	-s_srs "+init=epsg:23030 +towgs84=-84,-107,-120,0,0,0,0" 
	-t_srs "+init=epsg:3785 +towgs84=0,0,0,0,0,0,0" 
	-tr 250 250 

The epsg codes:
Input code (23030):
# ED50 / UTM zone 30N
<23030> +proj=utm +zone=30 +ellps=intl +units=m +no_defs  <>

Output code (3785):
# Spherical/Web Mercator
<3785> +proj=merc +lat_ts=0.0 +lon_0=0.0 +k=1.0 +x_0=0.0 +y_0=0.0 +a=6378137.0 +b=6378137.0 +units=m +nadgrids=@null +no_defs <>

Sorry for the insistence, and thanks a lot

Jorge wrote:
> The EPSG code 3785 is a custom one, but the same of 900913 (I didn't know it thanks), except for the "+wktext" term. What does it mean?
> OK, I'm lost with this issue. Could my calcs be wrong? I have, for example, this image:
> http://www.nebulared.com/tmp_geo/UTM_ED50_Balearic_Island.png
> And is georeferenced by this world file:
> http://www.nebulared.com/tmp_geo/UTM_ED50_Balearic_Island.wld
> The image is obtained for a MIF/MID couple of files with UTM projection, zone 30, ED50 datum (Mapinfo said... I don't know what 
> are the dX, dY, dZ parameters, buth they must be -84, -107, -120). Really, the raster file obtained from MIF/MID files isn't a
> PNG file, but I did the transform to "see" what I was doing.
> OK, I need to reproject the image, and the output image must be used to overlay it in a GMaps' frame. This is my last attempt:
> gdalwarp 
>	-s_srs "+init=epsg:23030 +towgs84=-84,-107,-120,0,0,0,0" 
>	-t_srs "+init=epsg:3785 +towgs84=0,0,0,0,0,0,0" 
>	-tr 250 250 
>	UTM_ED50_Balearic_Island.png
>	GMaps_Balearic_Island.tif
> Then, I transform the TIFF file in a PNG (transformation OK) and I have this image:
> http://www.nebulared.com/tmp_geo/GMaps_Balearic_Island.png
> But the image doesn't fit exactly in the map... Is there any error in this reprojection? If the projection is OK, I need to review
> the rest of the code...

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