On 16/05/08 17:26, M S wrote:
Hi everyone.
I had generated some contours from a DEM with r.contour. In the
resulting vector contour map, I get cat and level, where level is the
elevation value. I must be confused with the level terminology, because
I thought levels pertained to topological (2) or non-topological data
(1). However, in r.contour output, "level attribute" corresponds with
the contour elevation.
In GRASS the same words sometimes have different meanings according to
context. Generally for historical reasons...
Regardless, I'm able to query the lines in GRASS monitor to get the cat
and level (elevation) values for the contour lines, but in QGIS I'm
unable to query or identify the features. In QGIS, I am able to label
the lines on the "level" item though.
I refrained from cross posting to QGIS list, because it seems like
something I'm not understanding in GRASS vector model.
Any ideas why the features are (repeatably) unidentifiable in QGIS, but
are viewed and labeled without issue?
No idea, but I can confirm with the North Carolina demo data:
- elev_contour_3m: no data found
- any other line layer (streams, busroutesall, etc): I get the relevant info
After a bit of testing, it seems to me that this is due to the fact that
the contour lines have 3D points as vertexes, i.e.:
v.out.ascii elev_contour_3m format=standard
L 309 1
644845.39132067 228495 58
644850.5257363 228485 58
644855 228476.80568172 58
644856.10080552 228475 58
whereas the others have 2D points as vertexes, i.e.:
v.out.ascii busroutesall format=standard
L 40 1
638759.35668041 224267.86790137
638748.56434918 224206.16089597
638738.04094476 224149.69241332
638701.95659054 224155.1582149
638712.48508636 224219.60539241
638727.41956522 224217.30778103
638737.10320251 224271.95933017
So it seems to me that this is a flaw in QGIS' handling of this type of
data.
Moritz
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