[UW-GIS-L] random errors

[Jason Cross]

list,

In my first large-scale GIS effort, I am encountering some errors for 
which I cannot pinpoint the cause.

I am using the "buffer" and "erase" functions in sequence and repeating 
it many times; specifically, I am buffering a stream vector with some 
width, and then again with a width incrementally larger, and then erase 
the smaller buffer from the larger, leaving a rectangular "buffer" some 
distance from the stream vector.

For example, I buffer the stream vector with a 10ft wide buffer, and 
then again with a 20ft wide buffer.  I then erase the inner 10ft of the 
20ft buffer - leaving a 10ft wide buffer that is 10ft from the stream 
vector.  I then repeat this with 30ft and 20ft, moving away from the 
stream vector in 10ft increments.  I do this until some decision 
criteria are met (based on a zonal stats raster analysis). this is being 
repeated many times for each stream vector segment, and across many 
(tens of thousands) vector segments.

My problem is that the process is encountering an error in the buffering 
and/or erasing process and quitting even though the decision criteria is 
met. However, if I restart the process from the point where it quit, 
there appears to be no problem, and it will go to completion.  The 
result is a seemingly random error in the buffering and erasing 
functions.  Has anyone else encountered this?  any suggestions?

I am taking care to conserve memory, and storing intermediate buffers 
"in memory" and deleting after iterations, so I don't see a memory drain 
on the system.

Thanks for any suggestions.

Jason Cross