[GRASSLIST:5792] Geometry/topology/Mapserver

Hi All,

A mixed bag of questions!

(1) A plain question: in GRASS 5.0, where is the vector geometry and
topological structure stored? Vector line info is stored in dig files, but similarly
where is the geometry information.

(2) Why cant MapServer see PostGRASS/PostGIS polygons, but can only see
lines, boundaries and points?

(3) Cannot MapServer access GRASS vector and site data? If not why is it so?

(4) What exactly is meant by saying that GRASS 5.0 does not have 2.5 and 3D
vector support?

It would be great to have answers from the list.
  
Regards

Pradeep
FHT-Stuttgart
anprs110@mars.rz.fht-stuttgart.de

--
'..what the caterpillar calls the
end of life the butterfly calls the
beginning...' - Richard Bach

A.P.Pradeep Kumar
Zi.300, Bochumerstr. 3,
Hallschlag, D-70376, Stuttgart,
Germany. Handy: 0049-179-7906774
E-mail: geo_pradeep@hotmail.com
        appradeepkumar@yahoo.com

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On Monday 17 March 2003 12:22 pm, pradeep anakkathil wrote:

Hi All,

A mixed bag of questions!

(2) Why cant MapServer see PostGRASS/PostGIS polygons, but can only see
lines, boundaries and points?

Note: PostGIS is supported by 5.1.

PostGIS is not topological, GRASS is topological. GRASS stores
boundaries of areas in PostGIS and topology (areas) are
built and stored in GRASS. MapServer accesses PostGIS directly
and doesn't know about topology stored in GRASS.
If you want to use GRASS areas in MapServer you can:
1) Export areas to polygon layer in PostGIS or shapefile (v.out.ogr)
2) Ask and pay Frank to add vector support for GRASS 5.1 to OGR
3) Write topology extension for PostGIS.

Radim

Thanks Radim for the very clear reply! I am writing out a blank cheque for
Frank :slight_smile:

Pradeep

On Monday 17 March 2003 12:22 pm, pradeep anakkathil wrote:
> Hi All,
>
> A mixed bag of questions!
>
> (2) Why cant MapServer see PostGRASS/PostGIS polygons, but can only see
> lines, boundaries and points?

Note: PostGIS is supported by 5.1.

PostGIS is not topological, GRASS is topological. GRASS stores
boundaries of areas in PostGIS and topology (areas) are
built and stored in GRASS. MapServer accesses PostGIS directly
and doesn't know about topology stored in GRASS.
If you want to use GRASS areas in MapServer you can:
1) Export areas to polygon layer in PostGIS or shapefile (v.out.ogr)
2) Ask and pay Frank to add vector support for GRASS 5.1 to OGR
3) Write topology extension for PostGIS.

Radim

--
'..what the caterpillar calls the
end of life the butterfly calls the
beginning...' - Richard Bach

A.P.Pradeep Kumar
Zi.300, Bochumerstr. 3,
Hallschlag, D-70376, Stuttgart,
Germany. Handy: 0049-179-7906774
E-mail: geo_pradeep@hotmail.com
        appradeepkumar@yahoo.com

+++ GMX - Mail, Messaging & more http://www.gmx.net +++
Bitte lächeln! Fotogalerie online mit GMX ohne eigene Homepage!

On Mon, Mar 17, 2003 at 12:22:30PM +0100, pradeep anakkathil wrote:

Hi All,

A mixed bag of questions!

(1) A plain question: in GRASS 5.0, where is the vector geometry and
topological structure stored? Vector line info is stored in dig files, but similarly
where is the geometry information.

in
directory function
-------------------------
dig binary arc file
dig_ascii ascii arc file
dig_att vector category attribute file
dig_cats vector category labels
dig_plus vector index/pointer file
reg digitizer registration points

You find this and more details in
http://grass.itc.it/gdp/online.html
-> GRASS 5 Programmer's Manual

(2) Why cant MapServer see PostGRASS/PostGIS polygons, but can only see
lines, boundaries and points?

[answered by Radim]

(3) Cannot MapServer access GRASS vector and site data? If not why is it so?

Because the libgrass library
http://grass.itc.it/related_projects.html
-> libgrass

was not completed for vector and site data support. You may update it
to 5.1 or pay Frank Warmerdam to do that. In 5.1 sites are managed as
vector sites, the 5.0 sites format no longer exists (but can of course
be converted).

(4) What exactly is meant by saying that GRASS 5.0 does not have 2.5 and 3D
vector support?

It means that GRASS 5.0 supports only 2D vectors (which are flat on the
ground).

Hope this answers the questions,

Markus Neteler