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

[Jose Gonçalves]

I think your problem is the incorrect georeferencing of your initial image.
I downloaded it from your site:

http://www.nebulared.com/tmp_geo/UTM_ED50_Balearic_Island.png

loaded it in ArcGIS, gave it coordinate system UTM-30N-ED50 and overlaid
boundaries. It becomes obvious that the image is not correctly
geo-referenced and it seems that the coordinates in the world file are of
the bottom left corner and not top left as it should be.
See the attached jpeg image with printscreens (original and after shifting).

Regards

Jose' Gonçalves



2008/5/30 Jorge <jorge.arevalo at gmail.com>:

> Now, the results in Google Earth:
>
> The image before reproyecting (UTM zone 30 datum ED50)
> http://www.nebulared.com/tmp_geo/Balearic_Island_UTM_ED50.png
>
> The image reproyected
> http://www.nebulared.com/tmp_geo/Balearic_Island_Reprojected.png
>
> 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:
> 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
>    -co INTERLEAVE=PIXEL        Balearic_Island_UTM_ED50.png
>        Balearic_Island_Reprojected.png
>
> 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
>
> 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
>>    -co INTERLEAVE=PIXEL        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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