[GRASS-user] I do not understand how region/projection/coordinate system are intertwined

[Fridtjof Schiefenhövel]

Hello there!

it seems I can't solve this problem:

->create a location with a mercator projection (i want to have degrees as the coordinate system)

->import landsat geotiffs

->have degrees as units showing (e.g. when moving the mouse)

this is what I did:

-created a location using the projection/datum from a georeferenced file (the landsat geotiff). 

-created a location selecting mercator projection

here is what "g.region -p" showed:
projection: 99 (Mercator)
zone:       0
datum:      wgs84
ellipsoid:  wgs84
north:      0
south:      -12.5
west:       125
east:       150
nsres:      12.5
ewres:      12.5
rows:       1
cols:       2
cells:      2

-ran v.in.region in the source location
{trying r.proj without it would give me an error saying the imported region is out of bounds}

-imported the vector map in the target location

-set region to imported vector map

-ran r.proj to import/reproject the landsat geotiff from the source location.

here is what "g.region -p" showed now:
projection: 99 (Mercator)
zone:       0
datum:      wgs84
ellipsoid:  wgs84
north:      -375086.40793588
south:      -583681.58556862
west:       -122131.46631847
east:       111149.12622161
nsres:      12.49971103
ewres:      12.50029968
rows:       16688
cols:       18662
cells:      311431456

I do not understand, how can these bound values be even accepted when I chose Mercator projection and degrees coordinate system in the first place?

Thanks!