[GRASS-user] query raster cell and its neighbors by point

[Nikos Alexandris]

[meant to hit the list as well!]

Shaun Langley wrote:
> >>> I need to easily query a raster and return both the value of the cell
> >>> and the aggregate value of the 8-cell neighborhood, given a set of point
> >>> coordinates.

Nikos Alexandris wrote:
> >> What kind of an aggregation exactly?  Maybe not straight-through, but

Shaun Langley wrote:
> > Since my input raster is binary (0s and 1s), and I need to know how many
> > of the neighboring cells are 1s, it's sufficient to simply compute the sum
> > of the overall neighborhood. 

Since you have a binary map (as you wrote in your latest post), all easier (me 
thinks).

r.neighbors (in G7) can do that:

# turn your co-ordinates into a raster map if they aren't already
# ...simply a binary would be sufficient I guess

# sum the 8 neighbors for each point of interest
r.neighbors input=QueriedRaster selection=CellsOfInterest 
output=SumOf8Neighbors method=sum

However, I got confused a bit because a) I though it's a more complex map than 
binary/boolean and b) you asked also for returning "the value of the cell"...

If your binary map is a "True/False" map, why not setting all those 0s to NULL 
(using "r.null setnull=0")?  Then, if your Raster-To-Be-Queried has only 1s, 
then you know that it's always "1" the cell that is queried (if it is not 
NULL).

I hope I got it right what you are after.
Best, Nikos
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