[GRASS-dev] Re: terminology issues in grass7

[Markus GRASS]

Moritz Lennert wrote:
>> It seems that this behaviour depends on the feature types defined with
>> type option. In a quick test with the spearfish dataset, boundaries
>> having no cats are always displayed by default, but if I select layer=2
>> type=area instead of type=point,line,boundary,centroid,area,face, I get
>> only the areas with a cat value in layer 2 and no boundaries, no lines,
>> nothing else is displayed, and it is not necessary to use cat=1-9999.
>
> But how you deal with the situation I described, i.e. one boundary
> segment of the polygons has a cat value in layer 2 ?
Probably in the way you describe :-) Apparently boundaries are by
default displayed for every layer if boundary is included in the type
option and the cat option is not used. AFAIKT, boundaries only get a cat
value if they are not only a boundary but also have a different meaning
e.g. a road. So it seems your example is a special case where you only
get the expected display with layer=2 type=boundary cat=1-9999. For
areas, the cat option is apparently not needed. I haven't done extensive
testing, but is seems that boundaries are treated a bit differently by
d.vect than other types.

Markus M

> I.e.
>
> GRASS 6.5.svn (spearfish60):~ > v.category testlayers option=report
> Layer/table: 1/testlayers
> type       count        min        max
> point          0          0          0
> line           0          0          0
> boundary       0          0          0
> centroid       2          1          2
> area           0          0          0
> all            2          1          2
> Layer: 2
> type       count        min        max
> point          0          0          0
> line           0          0          0
> boundary       1          1          1
> centroid       0          0          0
> area           0          0          0
> all            1          1          1
>
> d.vect testlayers layer=1
> d.vect testlayers layer=2 type=boundary cat=1-9999 col=red width=3
>
> gives:
> http://geog-pc40.ulb.ac.be/grass/misc/testlayers1.png
>
> I need to declare either the boundary type (or no type at all) to see
> anything in layer 2, but then it shows all boundaries:
>
> http://geog-pc40.ulb.ac.be/grass/misc/testlayers2.png
>
> Moritz