[GRASS-user] v.patch drops boundary vector regions

[J. Brian Adams]

Thanks for the suggestion.

I tried running v.clean both after the patch and again before running  
v.patch, but there were still many dropped regions.  Curiously though,  
the regions that were dropped when I ran v.clean after the patch and  
those that occurred when running v.clean on the individual vector maps  
before patching were different.

An interesting characteristic of the data is that the pre-patched  
vector maps are all disjoin; there is no overlap between them.  I  
thought that this might be the culprit; that the dropped regions were  
not in either side of the patched vectors, but that was not the case.   
The dropped regions did exist in the pre-patched maps.

Any other thoughts?

On Mar 3, 2008, at 2:54 PM, Daniel Victoria wrote:

> I had some similar problems and they were related to topology. I found
> this in the v.patch man page:
>
> NOTES
> Any vectors that are duplicated among the maps being patched together
> (e.g., border lines) will have to be edited or removed after v.patch
> is run. Such editing can be done automatically using v.clean
> (tool=snap,break,rmdupl).
>
> Could that be it? It worked for me...
>
> Daniel
>
> On Thu, Feb 28, 2008 at 6:10 PM, J. Brian Adams  
> <brian.adams at fandm.edu> wrote:
>> I am experiencing an interesting problem with v.patch  I am trying to
>> patch together parcel maps from many (60) different townships into  
>> one
>> large county-wide parcel map.  When done, the county-wide vector map
>> drops many regions. It appears that the dropped regions are all very
>> large compared to most of the parcels and they overlap the boundaries
>> between townships.
>>
>> If it is important, the parcels maps were imported from shapefiles.
>>
>>
>>
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