[GRASS5] Grass 6 capabilities

[John Gillette]

Roger,
A quick note for now.  Area 3 and 4 (example 1) are drawn counter
clockwise.
I get negative area for area 3 in Grass5.3
Grass6 gives positive areas and you can display the direction of the
boundary.
I'm guessing the direction (clockwise vs counter clockwise) makes a
difference
in Grass5.  Will test.
John

-----Original Message-----
From: grass5-admin at grass.itc.it [mailto:grass5-admin at grass.itc.it] On
Behalf Of roger at spinn.net
Sent: Wednesday, November 02, 2005 1:12 PM
To: grass5 at grass.itc.it
Subject: [GRASS5] Grass 6 capabilities

It appears to me that the difficulties I originally described with
importing shape files to GRASS 5.3 are actually two or more different
problems.  I compiled two examples from a single imported shape file.

The first example below contains 4 complete polygons -- none of which
share a common node -- along with the necessary att and cats files.  The
polygons should be correctly supported by GRASS 5.  If, after the file
is set up as a valid GRASS vector file, you use d.what.vect to query the
left-most polygon the program will highlight all 4 polygons and produce
bad information about the polygon area.  Similar problems occur with
other modules that need to identify the polygons.

I don't have a clue what might cause the problem in GRASS 5.  My main
concern is whether GRASS 6 suffers the same result.

The second example contains 3 complete polygons composed of 7 lines.
The polygons all share a single node.  v.support reports several
"Unclosed area..."
errors.  In this case, I can resolve most of the errors by patching the
lines together so there is one line and one node for each polygon.  If
the polygons still share a node then v.support will still report errors
and fail to support the polygons.  If the sequence of points in the
lines are rotated so that the polygons do not share a node then polygons
can be supported.

The question with this is whether GRASS 6.X can import and support these
polygons without errors.

Thank you for your attention.


Roger Miller