Further efforts show that the distance upload is giving the correct value. I had the wrong flag checked (not as clear as it might be in the GUI). The other issues remain. But at least I CAN get useful analysis results.
Michael
On May 23, 2012, at 4:49 PM, <grass-dev-request@lists.osgeo.org>
wrote:
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Today’s Topics:
- broken stuff in vector modules (Michael Barton)
- another bug in v.distance (Michael Barton)
- v.distance values bogus in GRASS 6.4.2 also (Michael Barton)
From: Michael Barton Michael.Barton@asu.edu
Subject: [GRASS-dev] broken stuff in vector modules
Date: May 23, 2012 4:43:11 PM GMT+02:00
To: GRASS developers grass-developers grass-dev@lists.osgeo.org
Hi,
I don’t use the vector modules a lot and so they don’t get a lot of testing from me. I’m trying to do a project with someone that uses vector module and I find that some key things are broken. The following apply to GRASS 7 and GRASS 6.4.3.
v.distance gives bogus results for point to line distance uploads in a latlon region. For example, the distance uploaded from one site point to the nearest waterway is 5767967.05475, yet measuring this with the distance tool gives a much more reasonable 33211 m. The uploaded distance is off by an order of 173X – an enormous error. Nothing in the docs says that you cannot use v.distance with latlon regions.
To get around this, I thought I’d try to get the length of the line that connects each site point with its nearest waterway (a v.distance option). But when I tried to make a new table for this in the table manager, I find that I cannot access the “table description” section of the “manage layers” page in the attribute table manager. This is again because wx.StaticBox needs to be defined in a particular order or the Mac interface cannot access it. This has been a recurrent problem with wx.StaticBox. The StaticBox must be instantiated before any of its contents.
After creating a linked table using v.db.addtable instead of the attribute manager, I tried to modify the layer in the attribute table manager, but only received a message that “ is not a valid value”. Another bug.
I did manage to get a length value into the lines connecting the points and they are quite reasonable values. But of course I have no way that I can see to link the distance lines back to the points from which they were created with v.distance. So I still don’t have analysis results and my colleague is ready to try this in ArcGIS.
Any suggestion for a workaround would be much appreciated. And of course, the multiple bugs here need to be fixed.
Michael
C. Michael Barton
Visiting Scientist, Integrated Science Program
National Center for Atmospheric Research &
University Consortium for Atmospheric Research
303-497-2889 (voice)Director, Center for Social Dynamics & Complexity
Professor of Anthropology, School of Human Evolution & Social Change
Arizona State University
www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.eduFrom: Michael Barton Michael.Barton@asu.edu
Subject: [GRASS-dev] another bug in v.distance
Date: May 23, 2012 4:47:08 PM GMT+02:00
To: GRASS developers grass-developers grass-dev@lists.osgeo.org
Forgot to mention that the table selection pull-downs do not work in any version of the v.distance GUI–from 6.4.2 to 7.0
Michael
C. Michael Barton
Visiting Scientist, Integrated Science Program
National Center for Atmospheric Research &
University Consortium for Atmospheric Research
303-497-2889 (voice)Director, Center for Social Dynamics & Complexity
Professor of Anthropology, School of Human Evolution & Social Change
Arizona State University
www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.eduFrom: Michael Barton Michael.Barton@asu.edu
Subject: [GRASS-dev] v.distance values bogus in GRASS 6.4.2 also
Date: May 23, 2012 4:48:37 PM GMT+02:00
To: GRASS developers grass-developers grass-dev@lists.osgeo.org
So the values for point to line distances are just as bad in GRASS 6.4.2 as they are in GRASS 7. Any suggestions on how to get this information for a latlon region?
Michael
C. Michael Barton
Visiting Scientist, Integrated Science Program
National Center for Atmospheric Research &
University Consortium for Atmospheric Research
303-497-2889 (voice)Director, Center for Social Dynamics & Complexity
Professor of Anthropology, School of Human Evolution & Social Change
Arizona State University
www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu
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C. Michael Barton
Visiting Scientist, Integrated Science Program
National Center for Atmospheric Research &
University Consortium for Atmospheric Research
303-497-2889 (voice)
Director, Center for Social Dynamics & Complexity
Professor of Anthropology, School of Human Evolution & Social Change
Arizona State University
www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu