[GRASSLIST:5740] Re: region/location/projection problem

[Ian MacMillan]

Lizhong, so it sounds like there are a few things you need to know 
about GIS (I hope I am not being presumptuos).  The first thing is that 
all information is geocoded, or it isn't (not very profound).  Suppose 
a raster file has geocoding information in it, if you import it into a 
location that has the same projection parameters (i.e. latlong, wgs84), 
then the map will show up in the part of the world it is supposed to.  
Every location has a unique projection.  If your raster does not have 
projection data associated with it (like all jpegs, gifs, etc.), then 
you need to import it into an XY location (this location has no 
projection).  When importing into XY locations, all rasters come in 
with the top right corner at the origin (just because).  The reason it 
came in as -915-0 etc. is because your jpeg is a 915x587 pixel image.

Generally once you have a map in the XY location, you will want to 
project it to another location that has projection parameters that 
match some kind of real world map.  This is why you would use a GIS.  
If you just want to edit a raster without a projection, then GRASS is 
probably the wrong application.  I hope this is helpful.  If you have 
more specific questions about how to fit your jpeg into another 
location, there is info in the archives, or write back.

G'luck
-Ian



On Feb 11, 2005, at 7:34 AM, ljin at hunter.cuny.edu wrote:

> Hi,
> I am a new starter for GRASS. I create a new location and its mapset 
> in a new
> directory (database). The region was set as 0-10000 (W-E) and 0-10000 
> (S-N)
> when I did the creation. But after a map was imported (.jpg file, 
> downloaded
> from website), this imported map's region was -915-0 (W-E) and -587-0 
> (S-N), in
> the -/- area (the third quadrant of Cartesian coordinate system?). I 
> tried
> serveral times with similar downloaded maps, the imported maps always 
> falled in
> this area. How to sovle this problem? How to let the map "sit" in a 
> region as I
> want? Thanks for help.
> Lizhong Jin
>