[GRASSLIST:5590] how to import pre-projected map?

[Christian Keßler]

Hi there!

Just taking my first steps on grass... What I'm missing so far is the 
way to import a scanned, pre-projected map (Mercator projection, known 
parameters) and convert it into a grass map (as I understand this would 
be n,e angular coordinates - is this right?).

I've taken the tutorial steps on converting a scanned map:
- importing of scanned map into a temporary x,y location
- converting to a second location (with projection setup same as paper 
map projection) via i.points/i.rectify. To my understanding this step 
(at least for 1st order transformation) only corrects for basic 
transformation error (rotation, scaling, translation). What is still 
missing is the conversion from Mercator projection to direct angular 
coordinate raster map data.

What I would i.rectify to do is to look up the projection in the target 
location, and do an additional transformation to correct for this. like 
that: a) scaling/rotation/translation for scanning error b) 
elipsoid-projected x,y coordinate to n,e angular coordinates (in my 
case of mercator projection in target location).

So i.rectify didn't bring me there so far. What's the way to go for 
calibration/conversion from a pre-projected map to a calibrated grass 
raster map?

Bye & Thanks, Christian