vactor files

[David D Gray]

Hi Paola

Paola Lecca wrote:
> 
> Dear listers,
> 
> I obtained some vector files, changing MIF files (MapInfo TAB) firstly into shape files and secondly into GRASS vector files with the command v.in.shape. I'm using the last modified version of this command (version of few weeks ago).
> 
> Using v.to.rast, I obtained their raster version. When I visualize it, in many cases I see that the raster doesn't fill the entire space into the vector boundaries. In other words, the raster map doesn't cover the whole area contained by the vector lines.
>

By not covering I assume you mean there are areas that have not been
assigned a cell value, and so take on the NULL value color( usually
white)?

> What kind of problems can the vector map have ?
> 

Most likely the polygons affected have not been labelled. This is
usually because the input polygon had incorrect topology. You could
check this with v.digit. Use the Customise->Select Backdrop option to
set the rasterised map as a backdrop, and Toolbox->Display open area
lines to view lines that haven't been assigned areas. 

> Is there anyone that has dealt with similar problems and that might help me ?
> 

Try adjusting some of the parameters on the v.in.shape import.

scale=200
sliver= 0.01 - 0.1
snap= set this to the original snap tolerance of the input map if you
know it. Otherwise start at a scale of 3.0 for 1:10,000, so  6.0 for
1:20,000 etc.

You will get different results with these values and will have to play
around with them to get the best results.

Some errors might remain though because v.in.shape is good at fixing
problems near nodes, or edge junctions, but can't fix problems in the
middle of lines yet.


David

PS. We are developing a filter for direct import of Mapinfo data
(MIF/MID). This will be announced on the list when available.

D.