query by distance

[Edmondo]

Hi All,
there is an easy way to select (on a raster map) all features into a certain radius from a specific point?

Thanks

Bye

Edmondo

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[Nikos Alexandris]

On Thu, 2008-10-09 at 15:24 +0200, Edmondo Elisei wrote:
> Hi All,
> there is an easy way to select (on a raster map) all features into a
> certain radius from a specific point?
>
> Thanks
>
> Bye
>
> Edmondo

Maybe something using r.buffer/v.buffer --> YourBuffer (rasterize if it
comes from v.buffer), then r.mapcalc MASK=YourBuffer, then operate
within the MASK?

Regards, Nikos


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[hamish_b]

Edmondo:
> > there is an easy way to select (on a raster map) all features into a
> > certain radius from a specific point?

Nikos:
> Maybe something using r.buffer/v.buffer --> YourBuffer (rasterize if it
> comes from v.buffer), then r.mapcalc MASK=YourBuffer, then operate
> within the MASK?


Hi,

fyi I've recently added a new addon module called r.what.vect.buffer.
  http://grass.osgeo.org/wiki/GRASS_AddOns#v.what.rast.buffer

The idea is to provide local environmental context to a series of vector
points.

v.what.rast or r.what + coord alone may return a spike in the raster data
without you knowing. What this script does is create a buffer around each
vector point and gather some stats about the raster cells nearby and
report them in a .csv table. Multiple raster maps can be sampled.
I assume the location is not lat/lon, and (in column names) that units
will be meters. (r.buffer would be lat/lon safe; but I used r.circle
because it allows starting from an exact coord not from the nearest cell)

v.rast.stats + v.buffer is problematic when input points' buffers overlap.


GRASS> v.what.rast.buffer --help

Description:
 Calculates univariate statistics of raster map(s) from buffers around vector points.
 Results are written to a file. Resolution is taken from each input map.

Keywords:
 vector, raster, statistics

Usage:
 v.what.rast.buffer input=name raster=name[,name,...] buffer=value
   [output=name] [fs=character] [--verbose] [--quiet]

Flags:
 --v   Verbose module output
 --q   Quiet module output

Parameters:
   input   Points vector map containing query positions
  raster   Name of raster map(s) to calculate statistics from
  buffer   Buffer distance in map units
           default: 100
  output   Name for output file (if omitted or "-" output to stdout)
      fs   Field separator in output file
           default: |


spearfish example:
  v.what.rast.buffer in=archsites rast=elevation.dem,slope out="-"


enjoy,
Hamish



     

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[Dylan Beaudette-2]

On Thursday 09 October 2008, Hamish wrote:

> Edmondo:
> > > there is an easy way to select (on a raster map) all features into a
> > > certain radius from a specific point?
>
> Nikos:
> > Maybe something using r.buffer/v.buffer --> YourBuffer (rasterize if it
> > comes from v.buffer), then r.mapcalc MASK=YourBuffer, then operate
> > within the MASK?
>
> Hi,
>
> fyi I've recently added a new addon module called r.what.vect.buffer.
>   http://grass.osgeo.org/wiki/GRASS_AddOns#v.what.rast.buffer
>
> The idea is to provide local environmental context to a series of vector
> points.
>
> v.what.rast or r.what + coord alone may return a spike in the raster data
> without you knowing. What this script does is create a buffer around each
> vector point and gather some stats about the raster cells nearby and
> report them in a .csv table. Multiple raster maps can be sampled.
> I assume the location is not lat/lon, and (in column names) that units
> will be meters. (r.buffer would be lat/lon safe; but I used r.circle
> because it allows starting from an exact coord not from the nearest cell)
>
> v.rast.stats + v.buffer is problematic when input points' buffers overlap.
>
>
> GRASS> v.what.rast.buffer --help
>
> Description:
>  Calculates univariate statistics of raster map(s) from buffers around
> vector points. Results are written to a file. Resolution is taken from each
> input map.
>
> Keywords:
>  vector, raster, statistics
>
> Usage:
>  v.what.rast.buffer input=name raster=name[,name,...] buffer=value
>    [output=name] [fs=character] [--verbose] [--quiet]
>
> Flags:
>  --v   Verbose module output
>  --q   Quiet module output
>
> Parameters:
>    input   Points vector map containing query positions
>   raster   Name of raster map(s) to calculate statistics from
>   buffer   Buffer distance in map units
>            default: 100
>   output   Name for output file (if omitted or "-" output to stdout)
>       fs   Field separator in output file
>            default: |
>
>
> spearfish example:
>   v.what.rast.buffer in=archsites rast=elevation.dem,slope out="-"
>
>
> enjoy,
> Hamish
>
>

Interesting! This functionality is also StarSpan, albeit not within a
raster-only context. It would be interesting to compare the results!

Cheers,

Dylan




--
Dylan Beaudette
Soil Resource Laboratory
http://casoilresource.lawr.ucdavis.edu/
University of California at Davis
530.754.7341
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