[R] writing polygons/segments to shapefiles (.shp) or other ArCGIS compatible file
B.Rowlingson at lancaster.ac.uk
Thu Feb 26 13:43:53 CET 2004
Patrick Giraudoux wrote:
> Thanks a lot for the hints. I will try. Actually I was focusing (in a first stage) on simple segments (small mammal traplines...).
> I turned the problem out writing some lines to export the coordinates into a "simple" GRASS ascii file, imported it into GRASS as
> vector file and then used the export tool to get shapefiles... Not that direct: needs to have GRASS installed and an elementary
> knowledge on the export/import commands in this open source GIS.
> It would be fantastic to have the reverse functions of Map2poly(Map), Map2lines(Map), Map2points(Map) read.shape (eg poly2map,
> lines2map, points2map, and write.map) to write shapefiles.... I must however admit that I don't know enough about shapefile formats
> and R programming to do this by myself... and I would unfortunately be really out of my current job in the university...
The shapelib library comes with command-line utilities for creating
shapefiles, so at a stretch you could use those:
% shpcreate fnord polygon # creates new shapefile
% shpadd fnord 0 0 1 0 1 1 0 1 # adds a unit square polygon
% shpdump fnord
Shapefile Type: Polygon # of Shapes: 1
File Bounds: ( 0.000, 0.000,0,0)
to ( 1.000, 1.000,0,0)
Shape:0 (Polygon) nVertices=4, nParts=1
Bounds:( 0.000, 0.000, 0, 0)
to ( 1.000, 1.000, 0, 0)
( 0.000, 0.000, 0, 0) Ring
( 1.000, 0.000, 0, 0)
( 1.000, 1.000, 0, 0)
( 0.000, 1.000, 0, 0)
So you could quite easily create shapefiles from some text format with
a bit of R that calls 'system' (on Unix at least). You wouldn't have to
deal with C and the shapelib directly. This might be a bit slow though.
You can also create the dbf library on the command line.
Shapefile creation is on my list of things that would be nice for my
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