[GRASS-user] Newbie with composite raster import

[Glynn Clements]

Adrian Lester wrote:

> Please excuse my newbiness. I have been reading documentation left, right
> and centre and I may be missing something but I can't find an obvious way
> to do this.
> 
> I have a set of high resolution digital maps (currently a matrix of about
> 200x400, each at 1280x1024 resolution). They are saved as GIF files,
> though that could be changed, and I know their centre and edge positions
> in terms of Lat/Long to a negligible error. These data are stored in a
> tab-delimited text file. The map fragments are in a transverse mercator
> projection though not UTM. They are plain image files with no geographic
> data geocoded into the format.
> 
> What I want to do is to import them automatically via shell-scripted
> commands to a Grass raster layer(s?) in order to cover the region over
> which they spread, so that within grass I can work with it as a contiguous
> area.
> 
> I have found information about importing scanned maps with graphical
> picking of corners but this is both far too time consuming and unnecessary
> for what I am attempting (the maps are 'square', not scanned, and I can
> provide their edge positions automatically). I have also found some
> indications that each raster image has to end up as its own layer... how
> does this work with groups, large numbers of map fragments etc? Do I have
> to join the raster images within Grass or can they be kept separate?
> 
> If someone could point me in the right direction in terms of which
> commands I need to use and whether this is possible, I'd be very grateful.
> I'm really looking forward to getting this lot into Grass so that I can
> start working with it and learning more!

To set the bounds of the imported maps, use r.region.

To merge multiple maps, use r.patch. If the images don't share a
common colour table (palette), you will probably need to recode them
first.

-- 
Glynn Clements <glynn at gclements.plus.com>