[GRASS-user] importing geotif in grass, transformation parameters

Hamish hamish_b at yahoo.com
Wed Jun 25 22:52:29 EDT 2008

> For the grid I'm fine now, my error was that the units for
> the gridlines are not in degrees, but in rad or something like that.

no, they really are in degrees.  Like DDD:MM:SS.SSS.
So for a 2' grid you'd do 'size=0:02', for a 1deg grid size=1, etc.

> But my graph is twice much larger than I expected it (and
> looks quite ugly),

are you working at a high latitude?

> but probably it's due to the fact that Grass
> takes the same distance for 1degree in NS and EW in LongLat.

for the display window it uses "Plate Carrée" projection, ie equi-rectangular. As for "same distance" that isn't quite right to say it is the same, e.g. d.measure will give a correct result and the "back end" is doing the right thing even if it looks funny in the display.

3D Earth -> 2D raster array/paper ... why map projections were invented.

I suggest you reproject your data into a meter-based coordinate system appropriate for your region of study.

> It seams also impossible to draw a North arrow and a scale
> in LongLat.

Newer versions of GRASS let you draw the north arrow with d.barscale in a lat/lon location. A scalebar is wrong/impossible in lat/lon as the scale changes with latitude, so just use d.grid there. Also you can add a north arrow with d.graph and the north arrow or compass symbols.



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