On 01/25/2013 05:28 PM, John Nicholls wrote:
Hi
I am looking for some direction in applying a low pass filter to a
raster greyscale of geophysics data. The filtering objective is fairly
typical, aimed at removing influence of background noise normally
Striping is not really "noise". It's a systematic defect
in your data that cannot easily be removed with a simple
low-pass filter.
There is really no universal cure for this problem.
Unless your stripes are perfectly aligned with the
X or Y axis of your geographical region, simple
map algebra won't get you far, either.
The classic treatise on the subject is this one:
http://www.oimoen.com/PDFs/artifacts.pdf
Basically, the "trick" is using a low-pass and high-pass
filter whose shapes and sizes match those of your
stripes.
visible as linear striping or similar in a raster image created via
v.in.ascii then v.surf.idw or v.surf.bspline. I’ve tried r.mfilter
applying both 3x3 and 7x7 low pass filters as detailed in the GRASS
literature, and ask here if there are other methods either via r.mapcalc
or R which may prove more effective. I am not familiar with r.mapcalc,
nor R. I wonder if anybody has applied lowpass filters using either of
these 2 before, and would be kind enough to provide me with a lead in to
get started. Perhaps there a manual page I've not yet got to. Still a
long way to go with GRASS, but it really is superb for the limited
vector and raster analysis I need.
It's also superb for very advanced vector and raster
analyses ;)
Cheers,
Ben
Grass version I am using is 6.4.2 on Ubuntu.
Many thanks in advance,
JohnN
--
Benjamin Ducke
{*} Geospatial Consultant
{*} GIS Developer
[email protected]
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