[GRASS-user] Re: Importing lines from database
hamish_b at yahoo.com
Fri May 29 19:01:53 EDT 2009
> So IIUC, it's not possible to keep attributes for each point along a
> lines vector, so that one can select points along a line that meet
> certain criteria.
no, vertices can not have cats, only one cat (DB key index) per line.
you need two maps: one with the line, another with the vertices as points.
see the v.in.garmin, v.in.gpsbabel scripts for importing tracks or
"tracks as points".
> For example, to be able to show (or do calculations) a line joining
> points that are have values "A" in column 3 and values "Z" in column 4.
v.extract where='col3 = 'A' AND col4 = 'Z'
v.out.ascii | v.in.mapgen
but do worry about the order of points; try to sort by cat (if sequentially
added) or by timestamp. otherwise you will have lines going everywhere in
a big mess.
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