On Wed, Sep 18, 2013 at 11:41 AM, Moritz Lennert <mlenn...@club.worldonline.be> wrote: > On 18/09/13 10:51, Luca Delucchi wrote: >> >> On 17 September 2013 22:10, Markus Neteler<nete...@osgeo.org> wrote: >>> >>> Hi, >>> >>> I came across this question: >>> >>> >>> http://gis.stackexchange.com/questions/71734/how-to-calculate-mean-coordinates-from-big-point-datasets >>> >>> and wondered if this approach would be the fasted: >>> >>> # http://grass.osgeo.org/sampledata/north_carolina/points.las >>> v.in.lidar input=points.las output=lidarpoints -o >>> ... >>> Number of points: 1287775 >>> ... >>> >>> Now I would use >>> v.univar -d lidarpoints type=point >>> >>> (still calculating here...) >>> >>> Is it the best way? >>> >> >> maybe v.median [0] could help? >> >> >> [1] >> http://trac.osgeo.org/grass/browser/grass-addons/grass7/vector/v.median > > > Right. > > Here's a little test: > > $time v.median in=elev_lid792_randpts > 638648.500000|220378.500000
Should be 638648|220378. It seems that numpy gets the median wrong... > > real 0m0.249s > user 0m0.180s > sys 0m0.044s > > $time v.to.db elev_lid792_randpts op=coor -p | awk -F'|' 'BEGIN{SUMX=0; > SUMY=0; N=0} {N+=1;SUMX+=$2;SUMY+=$3} END{print SUMX/N, SUMY/N}' > Reading features... > 100% > 638544 220339 Should be 638650 220376 > > real 0m0.106s > user 0m0.100s > sys 0m0.020s > > Would be interesting to see results for big data. And AFAIK median is a bit > more difficult to do in awk. I imagine that replacing the median by the mean > in numpy is no problem (might be a flag to add to v.median). > The v.to.db + v.db.univar approach is working just fine, and provides correct results. About a little module to calculate centroid of polygon, center point of line and centroid (possibly weighted) for points, that would be easy because all the components are there, even though there are in theory alternatives to the current calculation of centroids for polygons. Markus M _______________________________________________ grass-dev mailing list grass-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-dev