[GRASSLIST:2384] Re: Problems Importing GeoTIFF

[Eric G. Miller]

On Tue, Sep 04, 2001 at 12:38:59PM +0200, postogna at libero. wrote:
> Hello ...
>    I would like to describe  a problem I'm facing importing GeoTiff 
> files, to see if someone can advise me on some wrong procedures or if 
> it is a GRASS Bug ...
> 
> The background is this :
> 1)I have an ADRG CD with a map of an area.
> 2)Using NIMA MUSE (Windows version) I extract the region I'm interested 
> specifying lat/long and a zoom factor of 0.5 ... I cannot use 1.0 
> because the map than gets too big ( more than 150 Megs).
> 3) I export it with NIMA MUSE into GeoTIFF.
> 
> Now the GRASS part comes:
> Info: I'm running GRASS5.0.0Pre1 on a LINUX Box (AMD Duron 800 MHz 128 
> MBRAM MATROX G450 32MBram)
> 
> 4) I defined a default region (lat/lon) according to the file I have
> 5) I load the map with r.in.gdal
> 6) When I go to display the map all is fine unless for a kind of 
> distortion of the picture (like if the aspect ratio is not maintained). 
> I noticed that because the area I'm interested include an air field and 
> the corners of the air-strip which are supposed to be 90deg. are wider.
> 
> 7) if, on the contrary, I define a region just x/y of the size of the 
> map I convert the map using r.in.tiff (which seams not to get the 
> georeferencing from the header) and displays it ... all is ok no 
> distortion ...
> 
> For my purposes I can work also with a X/Y projection since I'm trying 
> to draw profiles and LOS (this require another mail by itself...) but 
> I'll prefer any how to be georeferenced ...
> 
>  I'll appreciate any possible help .. best regards Fulvio Postogna

If the data is really in geodetic coordinates, then GRASS will adjust
for the differences in distance in the X and Y directions.  This might
account for the apparent distortion you are seeing.  If, on the other
hand, the data is actually a projected lat/lon (Azimuthal Equidistant,
Lambert, etc...) GRASS shouldn't make this adjustment.

BTW, r.in.tiff doesn't read GeoTIFF, it just reads normal tiffs images
and adjusts the region accordingly if there is a TIFF World File (not
the same as being a GeoTIFF).

-- 
Eric G. Miller <egm2 at jps.net>