Vector FAQ GRASS6: Difference between revisions
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'''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''': Solved since the 'cat' column is linking both (also stored in the geometric part). | '''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> | ||
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You can choose that. But supporting other formats is not bad! GRASS's vector format is topological, which opens doors to all sorts of analyses which a non-topological format (like PostGIS) does not. You can still link a vector to an external RDBMS with {{cmd|v.db.connect}} or directly to a PostGIS data source with {{cmd|v.external}}. | You can choose that. But supporting other formats is not bad! GRASS's vector format is topological, which opens doors to all sorts of analyses which a non-topological format (like PostGIS) does not. You can still link a vector to an external RDBMS with {{cmd|v.db.connect}} or directly to a PostGIS data source with {{cmd|v.external}}. | ||
'''Q''': Why can't I have layers called 1516? | |||
'''A''': The naming convention for vector maps requires that map names start with a character, not a number (map name scheme: [A-Za-z][A-Za-z0-9_]*). Reason: GRASS uses SQL which does not permit names starting with a number or symbol. | |||
'''Q''': Can you save color rules in vector files?<br> | '''Q''': Can you save color rules in vector files?<br> | ||
'''A''': Yes, see GRASSRGB column in the {{cmd|d.vect}} manual page | '''A''': Yes, see GRASSRGB column in the {{cmd|d.vect}} manual page | ||
'''Q''': It is well known that v.support often | '''Q''': It is well known that {{cmd|v.support}} in GRASS 5 often reported errors and cannot build topology. Is this problem addressed in GRASS 6?<br> | ||
'''A''': Yes. v.build is way better | '''A''': Yes. {{cmd|v.build}} is way better | ||
'''Q''': Why do we need support for so many formats and databases? One format + one database is enough.<br> | '''Q''': Why do we need support for so many formats and databases? One format + one database is enough.<br> | ||
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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: v.out.ogr | '''A''': yes: {{cmd|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.<br> | '''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 area (Example: roads, rivers etc) how | '''A''': If you have lines which are part of areas and lines which are not part of area (Example: roads, rivers etc) how could 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> | ||
'''A''': more or less. Not exciting yet, you are welcome to contribute | '''A''': more or less. Not exciting yet, you are welcome to contribute. See also [[Addons]] | ||
'''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), use v.in.ogr or v.in.dxf to import or v.extrude to extrude from 2D. | '''A''': 3D faces yes (e.g. CAD-style 3D buildings etc), use {{cmd|v.in.ogr}} or {{cmd|v.in.dxf}} to import or {{cmd|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 - v.build.polyline | '''A''': Yes - {{cmd|v.build.polyline}} | ||
'''Q''': Does any support for overlay/analyses exist in GRASS 6?<br> | '''Q''': Does any support for overlay/analyses exist in GRASS 6?<br> | ||
'''A''': yes - v.overlay and v.select | '''A''': yes - {{cmd|v.overlay}} and {{cmd|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, Microsoft via ODBC | '''A''': Oracle via OGR, Microsoft via ODBC, see {{cmd|grass-sql}} | ||
'''Q''': Are there images and other arbitrary documents supported as attributes?<br> | '''Q''': Are there images and other arbitrary documents supported as attributes?<br> | ||
'''A''': no (not yet?) | '''A''': no (not yet?). Perhaps add blob support? | ||
'''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 - v.external | '''A''': pseudotopology is built - {{cmd|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.*, v.lrs.*) | '''A''': yes (see {{cmd|d.path}}, v.net.*, v.lrs.*) | ||
'''Q''': Will be possible to read attributes from ArcInfo coverages | '''Q''': Will be possible to read attributes from ArcInfo coverages?<br> | ||
'''A''': yes, use v.in.ogr | '''A''': yes, use {{cmd|v.in.ogr}} | ||
'''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 and http:// | '''A''': Try http://www.ing.unitn.it/~grass/conferences/GRASS2002/proceedings/proceedings/pdfs/Blazek_Radim.pdf and http://download.osgeo.org/grass/grass6_progman/ ("GRASS 6 Vector Architecture") | ||
[[Category:FAQ]] | [[Category:FAQ]] | ||
Revision as of 09:50, 7 April 2009
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! GRASS's vector format is topological, which opens doors to all sorts of analyses which a non-topological format (like PostGIS) does not. You can still link a vector to an external RDBMS with v.db.connect or directly to a PostGIS data source with v.external.
Q: Why can't I have layers called 1516? A: The naming convention for vector maps requires that map names start with a character, not a number (map name scheme: [A-Za-z][A-Za-z0-9_]*). Reason: GRASS uses SQL which does not permit names starting with a number or symbol.
Q: Can you save color rules in vector files?
A: Yes, see GRASSRGB column in the d.vect manual page
Q: It is well known that v.support in GRASS 5 often reported 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 could 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. See also Addons
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, see grass-sql
Q: Are there images and other arbitrary documents supported as attributes?
A: no (not yet?). Perhaps add blob support?
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?
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://download.osgeo.org/grass/grass6_progman/ ("GRASS 6 Vector Architecture")