Difference between revisions of "Vector FAQ GRASS6"

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'''Q''':GRASS 5.7 vector architecture - FAQ: Why on earth topological model!? It introduces in fact many problems. Nontopological GIS is easier to use and all popular commercial GIS desktops like ArcView or Mapinfo use nontopological model. There are no advantages of topological model over nontopological. In addition, OpenGIS specification is not topological, so GRASS may never conform Open GIS once topological model is used.<br>
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'''Q''':GRASS 6 vector architecture - FAQ: Why on earth topological model!? It introduces in fact many problems. Nontopological GIS is easier to use and all popular proprietary GIS desktops like ArcView or Mapinfo use nontopological model. But there are some advantages of topological model over nontopological. In addition, OpenGIS specification is not topological, so GRASS may never conform Open GIS once topological model is used.<br>
 
'''A''': Well...
 
'''A''': Well...
  
 
'''Q''': Oh my God, how can you handle attributes and geometry by two separate libraries? This way can never write reliable implementation and there will be always inconsistencies between geometry and attributes.<br>
 
'''Q''': Oh my God, how can you handle attributes and geometry by two separate libraries? This way can never write reliable implementation and there will be always inconsistencies between geometry and attributes.<br>
'''A''':
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'''A''': Solved since the 'cat' column is linking both (also stored in the geometric part).
  
 
'''Q''': Everything is going RDBMS. The only modern and good enough solution is to store all data in relational database. Why do you spend all that time working on grass vector format if you can use PostGIS/Postgres?<br>
 
'''Q''': Everything is going RDBMS. The only modern and good enough solution is to store all data in relational database. Why do you spend all that time working on grass vector format if you can use PostGIS/Postgres?<br>
 
'''A''': mmm...Its a matter of choice. GRASS support PostGIS/Postgres.
 
'''A''': mmm...Its a matter of choice. GRASS support PostGIS/Postgres.
You can choose that. But supporting other format is not bad!
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You can choose that. But supporting other formats is not bad!
  
 
'''Q''': Is save color in vector files?<br>
 
'''Q''': Is save color in vector files?<br>
 
'''A''': Yes, see d.vect manual page
 
'''A''': Yes, see d.vect manual page
  
'''Q''': It is well known that v.support often reports errors and cannot build topology. Is this problem addressed in GRASS 5.7?<br>
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'''Q''': It is well known that v.support often reports errors and cannot build topology. Is this problem addressed in GRASS 6?<br>
 
'''A''': Yes. v.build is way better
 
'''A''': Yes. v.build is way better
  
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'''Q''': Is it possible to write/edit non native formats like shapefile, coverage or PostGIS?<br>
 
'''Q''': Is it possible to write/edit non native formats like shapefile, coverage or PostGIS?<br>
'''A''': yes
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'''A''': yes: v.out.ogr
  
'''Q''': Why are two line types (line and boundary) needed? Everything is easier with just one type, otherwise thousands of of hours must be spent to assign the right type to each line.<br>
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'''Q''': Why are two line types (line and boundary) needed? Everything is easier with just one type, otherwise thousands of hours must be spent to assign the right type to each line.<br>
'''A''': If you have lines which are part of areas and lines which are not part of
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'''A''': If you have lines which are part of areas and lines which are not part of area (Example: roads, rivers etc) how can you distinguish them?
area (Example: roads, rivers etc) how can you distinguish them?
 
  
 
'''Q''': Is it possible to generate TIN from raster DEM or 3D points?<br>
 
'''Q''': Is it possible to generate TIN from raster DEM or 3D points?<br>
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'''Q''': Are there volumes or other 3D objects supported?<br>
 
'''Q''': Are there volumes or other 3D objects supported?<br>
'''A''': 3D faces yes (e.g. CAD-style 3D buildings etc)
+
'''A''': 3D faces yes (e.g. CAD-style 3D buildings etc), use v.in.ogr or v.in.dxf to import or v.extrude to extrude from 2D.
  
 
'''Q''': Are there multiobjects like multipoint or multiline supported?<br>
 
'''Q''': Are there multiobjects like multipoint or multiline supported?<br>
'''A''': Yes I think so
+
'''A''': Yes - v.build.polyline
  
'''Q''': Does any support for overlay/analyses exist in GRASS 5.7?<br>
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'''Q''': Does any support for overlay/analyses exist in GRASS 6?<br>
'''A''': yes - v.overlay
+
'''A''': yes - v.overlay and v.select
  
 
'''Q''': Why do we need more categories attached to one element?<br>
 
'''Q''': Why do we need more categories attached to one element?<br>
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'''Q''': Is it supported Microsoft SQL Server / Oracle / Informix?<br>
 
'''Q''': Is it supported Microsoft SQL Server / Oracle / Informix?<br>
'''A''': Oracle via OGR
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'''A''': Oracle via OGR, Microsoft via ODBC
  
 
'''Q''': Are there images and other arbitrary documents supported as attributes?<br>
 
'''Q''': Are there images and other arbitrary documents supported as attributes?<br>
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'''Q''': How can be nontopological formats read by topological GIS without conversion?<br>
 
'''Q''': How can be nontopological formats read by topological GIS without conversion?<br>
'''A''': pseudotopology is built
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'''A''': pseudotopology is built - v.external
  
 
'''Q''': Are there routes like in ArcInfo supported?<br>
 
'''Q''': Are there routes like in ArcInfo supported?<br>
'''A''': yes (see d.path, v.net.*)
+
'''A''': yes (see d.path, v.net.*, v.lrs.*)
  
 
'''Q''': Will be possible to read attributes from ArcInfo coverages once OGR formats are supported?<br>
 
'''Q''': Will be possible to read attributes from ArcInfo coverages once OGR formats are supported?<br>
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'''Q''': Where can I find a description of the new vector format?<br>
 
'''Q''': Where can I find a description of the new vector format?<br>
'''A''': Try http://www.ing.unitn.it/~grass/conferences/GRASS2002/proceedings/proceedings/pdfs/Blazek_Radim.pdf
+
'''A''': Try http://www.ing.unitn.it/~grass/conferences/GRASS2002/proceedings/proceedings/pdfs/Blazek_Radim.pdf and http://grass.itc.it/devel/index.php#prog
  
  
 
[[Category:FAQ]]
 
[[Category:FAQ]]

Revision as of 06:26, 6 February 2007

Q:GRASS 6 vector architecture - FAQ: Why on earth topological model!? It introduces in fact many problems. Nontopological GIS is easier to use and all popular proprietary GIS desktops like ArcView or Mapinfo use nontopological model. But there are some advantages of topological model over nontopological. In addition, OpenGIS specification is not topological, so GRASS may never conform Open GIS once topological model is used.
A: Well...

Q: Oh my God, how can you handle attributes and geometry by two separate libraries? This way can never write reliable implementation and there will be always inconsistencies between geometry and attributes.
A: Solved since the 'cat' column is linking both (also stored in the geometric part).

Q: Everything is going RDBMS. The only modern and good enough solution is to store all data in relational database. Why do you spend all that time working on grass vector format if you can use PostGIS/Postgres?
A: mmm...Its a matter of choice. GRASS support PostGIS/Postgres. You can choose that. But supporting other formats is not bad!

Q: Is save color in vector files?
A: Yes, see d.vect manual page

Q: It is well known that v.support often reports errors and cannot build topology. Is this problem addressed in GRASS 6?
A: Yes. v.build is way better

Q: Why do we need support for so many formats and databases? One format + one database is enough.
A: Again its a matter of choice. What's wrong with supporting several formats?

Q: Is it possible to write/edit non native formats like shapefile, coverage or PostGIS?
A: yes: v.out.ogr

Q: Why are two line types (line and boundary) needed? Everything is easier with just one type, otherwise thousands of hours must be spent to assign the right type to each line.
A: If you have lines which are part of areas and lines which are not part of area (Example: roads, rivers etc) how can you distinguish them?

Q: Is it possible to generate TIN from raster DEM or 3D points?
A: more or less. Not exciting yet, you are welcome to contribute

Q: Are there volumes or other 3D objects supported?
A: 3D faces yes (e.g. CAD-style 3D buildings etc), use v.in.ogr or v.in.dxf to import or v.extrude to extrude from 2D.

Q: Are there multiobjects like multipoint or multiline supported?
A: Yes - v.build.polyline

Q: Does any support for overlay/analyses exist in GRASS 6?
A: yes - v.overlay and v.select

Q: Why do we need more categories attached to one element?
A: why not? Maybe you have different attributes to assign to one vector

Q: Is it supported Microsoft SQL Server / Oracle / Informix?
A: Oracle via OGR, Microsoft via ODBC

Q: Are there images and other arbitrary documents supported as attributes?
A: no (not yet?)

Q: How can be nontopological formats read by topological GIS without conversion?
A: pseudotopology is built - v.external

Q: Are there routes like in ArcInfo supported?
A: yes (see d.path, v.net.*, v.lrs.*)

Q: Will be possible to read attributes from ArcInfo coverages once OGR formats are supported?
A: yes, use v.in.ogr

Q: Where can I find a description of the new vector format?
A: Try http://www.ing.unitn.it/~grass/conferences/GRASS2002/proceedings/proceedings/pdfs/Blazek_Radim.pdf and http://grass.itc.it/devel/index.php#prog