I've not done this before and my trial-and-error approach doesn't work. I
need to add a reservoir to a stream system so I used the on-screen editing
feature to digitize the area, then rebuilt the topology. But, despite having
a fill color selected the new area is not filled.
I've attached a screenshot and the reservoir is the heavy-lined area near
the center of the map.
What step(s) have I missed here? I need to have that area filled so the
underlying stream channels are hidden, but it's the same blue color as the
stream channels.
I've not done this before and my trial-and-error approach doesn't work. I
need to add a reservoir to a stream system so I used the on-screen editing
feature to digitize the area, then rebuilt the topology. But, despite
having
a fill color selected the new area is not filled.
I've attached a screenshot and the reservoir is the heavy-lined area near
the center of the map.
What step(s) have I missed here? I need to have that area filled so the
underlying stream channels are hidden, but it's the same blue color as the
stream channels.
TIA,
Rich
In the GIS vector world you have points, lines and polygons. Typically
(in most) applications a single layer can only be 1 of the 3. What you
digitized is the outline of an area as a line feature. To make a
fillable polygon you can convert that or redigitize it in it's own
polygon layer.
These instructions are to achieve the visual look you describe, modeling
it as a reservoir for a network is a whole different story.
What you digitized is the outline of an area as a line feature. To make a
fillable polygon you can convert that or redigitize it in it's own polygon
layer.
I did not realize that I needed a new layer since the last time I
digitized in GRASS was with version 4.0 (whenever that was in the early
1990s).
I can digitize this in the lakes layer (where it should have already been
visible).
In the GIS vector world you have points, lines and
polygons. Typically (in most) applications a
single layer can only be 1 of the 3.
(but in GRASS vector maps you happily keep all 3(+)
types in a single map; for export to shapefile or
other GIS formats you may have to pick just one)
What you digitized is the outline of an area as a
line feature. To make a fillable polygon you can
convert that or redigitize it in it's own
polygon layer.
it should have been digitized as a boundary
(typically with no category), and a centroid added
somewhere within the area (must have a category
number).
make sure the area is closed (green "X" at the
begin/end node). if not re-edit and move one of the
red "X"s away then back again and allow it to snap.
v.type, v.category, and v.centroids may help, but
be careful not to convert the river network lines
to boundaries too
(but in GRASS vector maps you happily keep all 3(+) types in a single map;
for export to shapefile or other GIS formats you may have to pick just
one)
Hamish,
That's what I thought.
Anywho, I discovered the problem: some layers obscure others. I'm working
with the GUI layer manager (-6.5svn updated and rebuilt this morning) and
find no way to re-order the z-levels of the various layers.
I have a raster DEM and vectors for roads, streams, lakes, and specific
points of interest. I added the vectors to the display first (ctrl-shift-v),
then the raster (ctrl-shift-r). The raster covers the vectors and none of
them are visible. Despite looking at all menus on the Layer Manager and
Display I see no way to select the order of the layers.
The lakes layer (with the reservoir of interest) must have been covered by
another layer in my previous attempt.
What I need is the raster DEM on the bottom, with roads, streams, lakes,
and project points stacked above in that sequence. Where is the sequence
controlled?
I discovered the problem: some layers obscure others.
The problem is not that one layer covers another, but that one layer just
will not display. I've no idea why not. There are 4 vector layers but only 3
will display. It seems that the last to be added to the display doesn't.
