I have been trying to get the average slope for a polygon (actually all the
polygons) for a vector file created from r.poly from a classified satellite
image and I've just run out of steam. I've exported the slope file
(generated from r.slope.aspect) into arc/info and converted the grid to
points and exported the points (of course you have to export the ungenerate
file and the attribute file as two separate files then link them together
after importing them into access! ugh). It's the same process as simply:
r.to.sites -z input=slp30.testshed.rast output=slp30.testshed.site
s.out.ascii -di sites=slp30.testshed.site fs=, >slope.points.out
which would have been much better (expect for the ERROR: G_malloc: out of
memory message I kept getting with GRASS 5.0.0.pre3 on cygwin). I then have
to read this file in and compute the average slope for each of polygons. Is
there a way to do this in GRASS?
And more questions...
1) has anyone found decent docs on getting odbc to work with grass under
cygwin (do we have to use unixodbc or win32 odbc?)
2) what's the story on getting "native" multiple attribute support on any
version of grass 5.0/5.1?
3) is there a version of grass5.0.0 for cygwin yet? not one of the
pre-release version.
I would really love to turn arc/info all together but can't just yet. keep
up the great work.
Jeff.
Hi Jeff,
That sounds really complicated a procedure. How about using
r.average? You can use the result of your satellite image
classification directly as a base for the r.average command. No
worries about vectorizing.
In your workflow:
1. Classify the satellite image -> class.out
2. r.average base=class.out cover=slope.map out=average.slope
r.clump will give you a unique ID for each classified patch if the
average was that of the entire classes rather than the average of
each polygon.
Does this help?
Thomas
I have been trying to get the average slope for a polygon (actually
all the polygons) for a vector file created from r.poly from a
classified satellite image and I've just run out of steam. I've
exported the slope file (generated from r.slope.aspect) into arc/info
and converted the grid to points and exported the points (of course
you have to export the ungenerate file and the attribute file as two
separate files then link them together after importing them into
access! ugh). It's the same process as simply:
r.to.sites -z input=slp30.testshed.rast output=slp30.testshed.site
s.out.ascii -di sites=slp30.testshed.site fs=, >slope.points.out
which would have been much better (expect for the ERROR: G_malloc: out
of memory message I kept getting with GRASS 5.0.0.pre3 on cygwin). I
then have to read this file in and compute the average slope for each
of polygons. Is there a way to do this in GRASS?
And more questions...
1) has anyone found decent docs on getting odbc to work with grass
under cygwin (do we have to use unixodbc or win32 odbc?) 2) what's the
story on getting "native" multiple attribute support on any version of
grass 5.0/5.1? 3) is there a version of grass5.0.0 for cygwin yet? not
one of the pre-release version.
I would really love to turn arc/info all together but can't just yet.
keep up the great work.
Jeff.