[GRASS-dev] broken stuff in vector modules

[Michael Barton]

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.

1) 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. 

2) 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. 

3) 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 "<flag> 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.edu





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