Vilem Ded wrote
> Hi,
> I have set of points with attribute table (let just say with column "A" 
> containing 1s and 2s).
> I would love to use function v.hull in order to get two convex hulls
> (their
> faces). Basically apply function "by group". Unfortunatelly, I was not
> able
> to find simple way to do that.
> 
> First solution I came up with was scripting with for cycle using
> "category"
> - picking ids of points and then run:
> v.hull input=mypoints output=myhulls1 cat="1,3,40,etc"
> v.hull input=mypoints output=myhulls2 cat="2,4,41,etc"
> 
> Than I tried where clause:
> v.hull input=mypoints output=myhulls1 where="A<2"
> v.hull input=mypoints output=myhulls2 where="A>1"
> 
> Unfortunatelly, this clumsy solution (I have hounderds thousands of point 
> sets) does not work. All four lines gave me the same result (convex hull 
> created from all points).
> The only even more clumsy solution I succeded with was first use
> 'v.extract'
> and than apply 'v.hull' on newly created maps.
> 
> My questions:
> Is there a way how to effectively apply function(command) by group?
> Is the v.hull function supposed to work like this (ingnoring where and cat
> arguments)?

confirmed that where or cat seems not to work. please open a ticket for
this.




-----
best regards
Helmut
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