On 28/01/17 12:19, Helmut Kudrnovsky wrote:
For the centroid coordinates:
v.db.addcolumn YourMap column="x double precision, y double precision"
v.to.db YourMap op=coor col=x,y
just tried with some vectors in a wgs84 ll location:
v.report map=testcalculate option=coor
cat|id|x|y|l|r|t|b|x2|y2|x|y|z
1||9.8489673562|47.0568937369|9.0801356183|10.6452349706|47.6779179411|46.4101061965|9.85074274819765|47.0584209060437|9.85074274819765|47.0584209060437|0.0
2||11.8802743895|46.9879350674|11.0347074901|12.7965928607|47.8068606443|46.1987432153|11.8761701610656|46.990400528994|11.8761701610656|46.990400528994|0.0
3||9.7422504597|46.163754262|9.0475885875|10.3944050709|46.4383355922|45.9348643802|9.737413876863|46.16534963624|9.737413876863|46.16534963624|0.0
x and y are the centroid coordinates calculated by QGIS
x2 and y2 are the centroi coordinates calculated by v.to.db
and the last (identical to x2 and y2) reported by v.report
it's interesting that QGIS and GRASS calculates differnt centroid
coordinates.
any idea?
I don't know which tool you used in QGIS, but GRASS' centroids are not
guaranteed to be the geometrical centroid (aka "center of gravity" which
could sometimes fall outside the polygon). You might want to compare the
results of QGIS with those of the addon v.centerpoint.
For the bounding box coordinates, I don't know any easy way. Would be a
nice thing to have in v.to.db (see [1]).
yes indeed, would be a nice addition to v.to.db. updated the ticket.
taken from a little script coded some time ago:
######
# print bbox of vector layer geometries
######
if print_bbox_vector_geometries :
# open vector
vtopo = VectorTopo(vector)
vtopo.open(mode = 'r')
# loop thru vector geometries
for i in range(1, vcats_max_plus):
# get vector geometries area info
vect_geom_area = Area(v_id = i, c_mapinfo =
vtopo.c_mapinfo)
# get vector geometries bbox info
vect_geom_bb = vect_geom_area.bbox()
# bbox north, south, west, east
bb_north = vect_geom_bb.north
bb_south = vect_geom_bb.south
bb_west = vect_geom_bb.west
bb_east = vect_geom_bb.east
grass.message("cat %s: north: %s south: %s west: %s
east: %s" %(i,
bb_north, bb_south, bb_west, bb_east))
# close vector
vtopo.close()
so it's already in the vector data available, would be nice to have it in
v.to.db.
Yes, there's Vect_get_area_box in the Vlib (box.c), so it shouldn't be
too hard to integrate it.
Moritz
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