[GRASSLIST:1780] Re: v.out.arc GENERATE POLYGONS

[David D Gray]

Jaime Mejía wrote:
> 
> Good day, everyone
> 
> When I try to export an polygon's coverage
> as ARC/INFO generate, Grass exports the
> segments of the polygon, but not the
> correct secuence of vertexes of the polygon,
> neither the correct id of that polygon,
> so I can not re-create the coverage out from
> Grass.
> The generate format for polygons is like:
> 
> ID
> coord x of the first vertex,coord y of the first vertex
> coord x of the second vertex,coord y of the second vertex
> coord x of the third vertex,coord y of the third vertex
> ..
> ..
> coord x of the nth vertex,coord y of the nth vertex
> coord x of the first vertex,coord y of the first vertex
> END
> 
> For example:
> 
> 1
> 200.00,150.00
> 300.25,236.28
> 254.35,498.25
> 456.87,548.24
> 200.00,150.00
> END
> 2
> 325.25,365.25
> 365.25,547.56
> 658.78,659.85
> 325.25,365.25
> END
> 
> How could I get that?
> Or how can I manipulate the script?
> Or how can I manipulate the drawing
>         in order to write the file
>         the way I need?
> 
> Thank you,
> 

Hi Jaime

In fact the output of the ungenerate format is correctly represented by
the segments of the polygons as this is the original format that
Arc/Info stored vector spatial data representing area coverages, and the
ungenerate was a means of exporting/importing data in an ascii format.
In recent years it has sometimes started to appear in a format that
represents whole polygons, which I think has appeared because ArcView
and some other desktop GIS systems employ this way of representing
coverages (good for display and querying, but not so good for persistent
data as it easily becomes corrupt/inconsistent).

If you plan to import to Arc/Info, the form exported by GRASS should be
OK. This contains a file that contains the line segments (.lin), a list
of area label points in the .lab file and corresponding attribute values
in the .txt file. If you want to import to ArcView, it might be better
to generate a shapefile coverage, using v.out.shape.

Regards

David