excellent. thank you for the clarification. the parallels
to the the esri software help too, since thats the world i'm migrating
away from (after 10 years).<br>
<br>
so you have layers that can be linked to various tables. if one
does a v.patch command and now has two "layers" of lines, how can they
both be put on the same layer, or does that not even matter? i
guess its like if you have a polygon coverage in workstation.
then u can build it for lines (the .aat) and polygons (the .pat).
then u can add attributes and manipulate them for the different
attribute tables. however, since u cant have various "layers" of
the same datatype in a coverage, i think that is where i get confused.<br>
<br>
in trying to run this v.net.steiner, i have lines on seperate
layers. not sure if that is throwing the fucntion for a loop
because you have to specify the layer of arcs. <br>
<br>
thanks for the help.<br><br><div><span class="gmail_quote">On 6/18/06, <b class="gmail_sendername">David Finlayson</b> <<a href="mailto:david.p.finlayson@gmail.com">david.p.finlayson@gmail.com</a>> wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
I can't answer your specific question, but I think I can answer the general one.<br><br>Vector layers in GRASS lingo are equivalent to "joined" tables in<br>ArcGIS. In GRASS the geometry information is stored in the file system
<br>and attributes are stored in a database. The key linking the geometry<br>to the table is the category (often abbreviated to cat). The category<br>is equivalent to the Shapefile ObjectID.<br><br>You can have multiple tables linked to a single vector file hence the
<br>layer=number terminology.<br><br>Tools which work with the linkage between the vector and the attribute<br>table begin with:<br><br>v.db.*<br><br>Whereas, tools that work strictly with the database table are prefaced with:
<br><br>db.*<br><br>In many cases, the db.* commands can be replaced by SQL calls sent<br>directly to your database via conventional interfaces/GUI (nothing to<br>do with grass).<br><br>On 6/17/06, M S <<a href="mailto:mseibel@gmail.com">
mseibel@gmail.com</a>> wrote:<br>> (sorry if this is a bit of a cross post, but i put a similar question under<br>> v.net.steiner. since not everyone may realize its really a layer question i<br>> figure'd id repost and ask)
<br>><br>> can someone simplify an explanation about layers in grass vectors?<br>> i read about them on this page.<br>> <a href="http://www.geog.uni-hannover.de/grass/grass61/manuals/html61_user/vectorintro.html">
http://www.geog.uni-hannover.de/grass/grass61/manuals/html61_user/vectorintro.html</a><br>> its under the "attribute management" section. it seems like they have more<br>> to do with linking tables?<br>>
<br>> The reason i ask, is because i'm trying to input to the v.net.steiner<br>> function without success. the function (as i understand it) requires inputs<br>> of arc layer, and point layer, but all in same file.
<br>><br>> when opening the "network" grass vector in QGIS, it reveals that there are<br>> 3 layers. (which were built using v.patch to put them all together.)<br>> layer 0 (arcs) = lines connecting buildings to streets
<br>> layer 1 (arcs) = streets<br>> layer 1 (point) = buildings<br>><br>> because you specify the a(rc)layer and n(ode)layer, the fact that i have<br>> arcs in two layers seems like it is causing the function to bail.
<br>><br>> is there a way to put all the arcs on one layer? or is there something else<br>> taht i am missing. layers in vector data models are a foreign concept to me<br>> coming from the a/i workstation world.
<br>><br>> any help or clarification would be great! thanks in advance.<br>><br><br><br>--<br>David Finlayson<br></blockquote></div><br>