[GRASS-user] Smoothing algorithim to remove small spikes

Matthias Rumitz Matthias.Rumitz at dignum.de
Mon Oct 10 07:00:52 EDT 2011

... I gather, the "spike removal" you mention averages adjacent pixels (i.e. low-pass filtering).
But what you want would be "FourierTransformation" and therefore removing high frequency image components. Unfortunately I do not know whether there is such a feature already implemented.

Kind regards

Am 08.10.2011 20:14, schrieb spiderplant0:
Hi, I have a vector map that has some narrow features (boat jettys etc) that I wish to smooth out. Can anyone suggest a method of achieving this please? I have tried several of the algorithims in v.generalise without success. One of the problems I am experiencing is that small details seem to be treated similarly to large scale detail. See links to example using snakes method. Map prior to filtering... [map prior to filtering]  Map after filtering... [map after filtering]  Composite map.... [map composite]  At the bottom-left of the map I have small spikes that I want smoothed over. They have been smoothed out reasonably well but the large spike has been converted into a short fat spike. I.e. it has been reduced in size by around the same percentage as the small ones. Also at the top-right of the map, a huge area of land has been chopped off. Its as if the smoothing algorithm didnt take account of scale but just consider a number of vertices each side of the point and apply the filter without considering how far apart in metres the points are. What I'm looking for is a way to smooth out the small detail especially small spikes, but not chop out big areas of land at larger scales.
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