[GRASS5] r.in.gdal and negative values

[Hamish]

> > re. http://grass.itc.it/pipermail/grass5/2005-January/017029.html
> > 
> > 
> > Currently r.in.gdal imports unprojected data in the negative, i.e.
> > 0,0 is the top right of the image.
> > 
> > (unlike r.in.tiff|png in GRASS 5.4 which makes 0,0 bottom left)
> > 
> > This can be "fixed" with r.region by the user after import.
...
> > I don't understand the logic or intention here: who's supposed to be
> > 
> > getting set to negative and why?
> 
> As written: L1B data have a strange GCP organization. We should
> probably change the test to refuse L1B data completely as
> i.rectify is not suitable to recitfy AVHRR data.
> 
> The new gdalwarp/thin plate splines warper performs better (so
> a new error message could suggest exactly this).
...
> Frank wanted negative (I don't know why - maybe there is no reason).
> I suggest to change to positive values for all and to refuse L1B or,
> at least, issue a warning.

I think a warning is best. GRASS XY may still be used as a data-
exploration or translation software. In future i.rectify may be updated
with more methods. As a general rule, I don't like to enforce that
something is not possible just because I don't see why it is important
or how to do it myself.


> The story is:
> - Frank wrote the module with negative values in the XY case

I do remember a thread about this on the mailing list some time ago but
can't seem to find it in the archives. Bad choice of search words I
guess. Any hints? If we can't find Frank's reasoning, perhaps we should
wait a few days until he is back on-line. And then do it anyway :)

Found this:
 https://intevation.de/rt/webrt?serial_num=805



> - I added special treatment for AVHRR to make it work. Then I
>   discovered that polynomials perform bad for AVHRR. Finally
>   I organized partial fundings for the thin spline warper in GDAL
>   which works way better.

I plan on testing out the GDAL splines soon, will let you know how it
goes.



cheers,
Hamish