g.region shrink / expand parameter

[alf]

Hi,

it would be really nice to have a shrink/expand parameter in g.region for shrinking/expanding the current region.

Best,

Alessandro Frigeri

[martinl]

Do you mean something like

g.region n=n+1000

it's working.

[alf]

Martin,

Yes, that is basically what I was meaning, it's already there and works, and the manual describe it just fine! Maybe in future the shrink and expand parameters can be introduced fro a quickest working region trimming.

Ciao,

Alessandro

[martinl]

Replying to alf:

Maybe in future the shrink and expand parameters can be introduced fro a quickest working region trimming.

I agree, I would be able to imagine something like

# g.region n=n+10 s=s-10 w=w-10 e=e+10
g.region offset=10

# g.region n=n-10 s=s+10 w=w+10 e=e-10
g.region offset=-10

Make sense?

[dickeya]

To add to this idea, I think it would be very useful to grow/shrink the region based on number of pixels instead of current projection units. This would ensure exact alignment when changing a region with non-int units. I currently do this via python.

[alf]

Replying to martinl:

Replying to alf:

Maybe in future the shrink and expand parameters can be introduced fro a quickest working region trimming.

I agree, I would be able to imagine something like

# g.region n=n+10 s=s-10 w=w-10 e=e+10
g.region offset=10

# g.region n=n-10 s=s+10 w=w+10 e=e-10
g.region offset=-10

Make sense?

Yes Martin! For the parameter name I'd rather go with the term 'expand', and the following entry in the manual

(...) expand=value

Expand (positive offset value) or shrink (negative offset value) current region

(...)

Alessandro

[hamish]

g.region.grow module added to grass6 addons in r55843.

​http://grasswiki.osgeo.org/wiki/AddOns/GRASS_6#g.region.grow

Instead of rows=rows+2*n cols=cols+2*n (or rows=rows-2*n cols=cols-2*n) I took the easy way and made use of the g.region -a flag, which rounds outwards to the nearest whole-cell. Feel free to reopen the wish if you'd like to see a -c flag added to make the expand= (should it be called amount= or extent=?) refer to cells not map units.

Hamish