[GRASS-user] New User Getting Started

[Moritz Lennert]

On 24/06/08 20:25, Brock Anderson wrote:
> Hi Folks,
> 
> I'm new to GRASS, and I'm hoping somebody can give me some advice to get 
> me started...
> 
> I have two netcdf raster grids.  One is seafloor age, the other is 
> seafloor depth.  The files both cover the same geographic area, although 
> the grids are different resolutions.
> 
> What I want to do is plot a simple x-y graph of seafloor age vs. depth, 
> where each point in my graph represents the a seafloor age grid cell and 
> the intersecting seafloor depth cell.
> 
> Can this be done?  Can anyone suggest some basic steps to get me 
> started?  No instruction is too basic for me -- this is my first day 
> with GRASS.  I have just installed GRASS (and R, just in case it's 
> necessary), but otherwise I have no idea how to proceed.

I suppose your two files are georeferenced.

1) Create projected location using the "create new location 
using...georeferenced file"

2) Import both files with r.in.gdal (File->Import raster maps->Multiple 
formats with gdal)

3) Several possibilities for extracting your information
	- Use 'r.stats -n1  input=Age,Depth' to extract the values pixel by 
pixel (use the command line as this can crash your GUI if you have large 
images);
	- Use r.coin (Raster -> Reports and statistics-> Mutual category 
occurrences (coincidence)) to get the matrix of coincidence;
	- You also have r.regression.line to calculate the regression 
coefficients between the two, and r.covar to calculate 
covariance/correlation coefficients.

4) Use whatever graphics software you want to make a graph out of this 
information