[GRASS-user] Help with Georeferencing

[Hamish]

Matt wrote:
>  I'm using this to figure out how to georeference. The tutorials / wiki
> are useful but for someone new to GRASS there is a little detail lacking
> in the documentation.

anyone can edit the wiki, improve as necessary. for the website tutorials
not yet ported to the wiki or main module help pages, post a patch to the
bug tracker. there is no real documentation team here, only contributing
and appreciative users.


> I think my problem at the moment is that I've got a theoretical
> understanding of how groups and locations work but applying this
> to the menu structure/workflow within grass is another thing.

see the "quick intro" help pages:
  http://grass.osgeo.org/grass64/manuals/html64_user/index.html

beginning with "How to start with GRASS"
  and on the wiki:
http://grass.osgeo.org/wiki/Gis_Concepts
  which leads to:
http://grass.osgeo.org/wiki/Gis_Concepts#How_a_GRASS_project_is_organized
 
> Locations: basically a place in the grass database with an area (ie
> region) and a projection.

right.

> Data within the location is stored in groups.

no, locs contain mapsets. mapsets are just a collection of maps, perhaps
grouped by time, owner, data type, or local area of interest.
There is always a PERMANENT mapset which contains projection info for the
location and maps viewable from all mapsets. Typically you'll work in
another mapset from that.

Groups contain a series of raster maps covering the same area (e.g. red,
green, and blue bands of the same satellite image)

> ie, one raster split into RGB would be a group, 

yes, r.in.gdal often makes you a group if it is importing multiband data.

> an imported shapefile or possibly set of shapefiles would be another
> group.

no, they just live in the mapset as a bunch of vector maps.
 
> Locations need to be created when starting grass.

you need to have one to work with.

> Do I need to have a group created before I import data or, is there a
> group created when I import data?

r.in.gdal creates groups, or you can use i.group to manage them.

> I can import vector data easily enough and I'm not prompted to create a
> group usually, however I am having trouble creating a group using the
> i.group tool.

> If I start it form within the georectify
> tool it won't accept any input until I close the
> georectify window and it usually crashes.

typical suggestion then is to try and see if it works from the CLI,

> The man page doesn't have a cli example on how to create a
> group within the location (that I can remember, I'm away from my grass
> pc today).

look in the i.group help page, hopefully the georeferencer help page
links to that.


Hamish