Am 06.04.2011 21:56, schrieb Glynn Clements:
Johannes Radinger wrote:
I've got a first basic idea but it isn't working yet completetly.
I wanted to loop over the pointfile to use the single points for other
operations
like the r.stream.basins module. Most of these modules do also except
coordinates.
So here is one solution but hopefully someone know a better one:
1) add two new columns to the pointsfile and populate it with the X
and Y coordinate (v.db.addcol and v.to.db)
2) use v.db.select-command in a for loop and pipe the X.Y
coordinate-pair to a variable, like (to loop over the first 5 points
in a pointfile):
def main():
for i in range(5):
where ="rowid = "+str(i)
p = grass.pipe_command("v.db.select", flags="c", map=options['input'],
columns="X,Y", where=where, fs=",")
print p
It isn't working at the moment (I get<grass.script.core.Popen object
at 0x53f3f0>) but I don't think that is a problem of the for loop, it
is more a problem of the pipe-command because it is working when i use
run_command instead of pipe_command.
what is the problem with the pipe command?
pipe_command() returns the process object, not its output. You can
read the process' output via p.stdout. If you just want the process'
output as a string, use read_command() instead.
read_command() is roughly equivalent to `backticks` in the shell.
pipe_command() is useful if the process will return a lot of output or
if you want to process the output as it is generated (read_command()
won't return until the command has terminated)
Thank you for the info with read_command, i realized that option after i
wrote
the email. Do you think that is the best way to loop over points..?
/johannes
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