[R-sig-Geo] subsetting
Tomislav Hengl
T.Hengl at uva.nl
Fri Oct 24 10:18:27 CEST 2008
to get statistics of grids over polygons, you might also consider using the Grid Statistics for
Polygons method in SAGA GIS:
> rsaga.get.modules("shapes_grid")
$shapes_grid
code name interactive
1 0 Add Grid Values to Points FALSE
2 1 Get Grid Data for Shapes FALSE
3 2 Grid Statistics for Polygons FALSE
4 3 Grid Values to Points FALSE
5 4 Grid Values to Points (randomly) FALSE
6 5 Contour Lines from Grid FALSE
7 6 Vectorising Grid Classes FALSE
8 7 Clip Grid with Polygon FALSE
9 8 Gradient from Grid FALSE
> rsaga.get.usage("shapes_grid", 2)
*Note that SAGA can handle even large grids/polygons (up to 2GB size).
hth
Tom Hengl
http://spatial-analyst.net
-----Original Message-----
From: r-sig-geo-bounces at stat.math.ethz.ch [mailto:r-sig-geo-bounces at stat.math.ethz.ch] On Behalf Of
Pieter Beck
Sent: Thursday, October 23, 2008 9:15 PM
To: r-sig-geo at stat.math.ethz.ch
Subject: [R-sig-Geo] subsetting
Dear all,
I am a new user to the world of spatial applications of R and am wondering
about this trivial question:
What is the easiest way to subset a SpatialGridDataFrame, based on 4 corner
coordinates?
The reason I ask is that I want to do an overlay of a polygon file on a
large raster dataset, to extract summary statistics from it. Both files are
extremely large, however, and just applying overlay causes memory trouble. I
was hoping to loop through the polygons, subset the SpatialGridDataFrame
using the bounding box surrounding a polygon and then create the summary
statistics one polygon at-a-time. To do this, I'd need to subset the
SpatialGridDataFrame based on the bounding box corner coordinates.
Thanks in advance for the help,
Kind Regards,
Pieter Beck
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