[GRASSLIST:3857] Re: Doubt about importin radar images

[Paul Kelly]

Hello Javier

On Fri, 9 Jul 2004, javier garcia - CEBAS wrote:

> Hi all;
> I' ve imported some radar images into GRASS.
> The source are .png images and the four Lat/Lon coordinates of the corners,
> and my location is UTM projection European datum for Spain and Portugal.
> So I've done the following:
> First of all, I've done the conversion into my UTM projection with software
> GEOTRANS V2.2.4 of the four corners.
>
> 1) I've imported the png images
> 2) created a group and added all images to the group (i.group)
> 3) created a target in the destination UTM location (i.target)
> 4) executed i.points (marking the points and my GEOTRANS' calculated UTM
> coordinates)
> 5) executed i.rectify
> It seems that the result is good. But (I recognize I lack enough background
> about projections...) I'm asking myself if  I've got a concept error:
> Perhaps I shouldn't transform the coordinates and should directly use
> i.target i.points and i.rectify to pass the images into a Lat/lon location,
> as the source images are, and later on to convert (I don't know how) the
> raster Lat/Lon maps into the UTM European1950 datum for Spain and Portugal?

I think the method you used is the best, as it only involved one raster 
re-sampling step (i.rectify). If you did it the second proposed way (using 
an additional r.proj step) the raster would have been re-sampled twice and 
there would be more scope for errors and blurring of your data.

Paul