[GRASS5] Re: v.digit odd attribute behavior

[Radim Blazek]

On 3/3/06, Kirk R. Wythers <kwythers at umn.edu> wrote:
> Radim,
>
> I would like to hear your thoughts concerning what appears to be
> fairly odd behavior in v.digit. First some background.
>
> I am working with some vectors that were digitized by students using
> ESRI products. The students then saved their work as shape files. I
> am double checking their work and using v.digit (6.1.cvs) to make a
> few edits (where my interpretation is a little different from theirs)
> and add attributes to areas.
>
> The vector is connected to a single table in postgresql.
>
> In 90% of the cases were I select a centroid, or line, or an area,
> the expected results get printed to for form which pop up.
>
> However, in a few cases, when I select a centroid, the form pops up
> with 3 tabs at the top (Layer 1, Layer 1, Layer2)
>
> The two layer 1 tabs will different information in the fields
> (including different cat values), and the layer 2 tab, says "Database
> connection not defined"

This is all correct. v.in.ogr must clean the topology but it
preserves all input data. In this case there were 2 overlaping
areas in the input. GRASS created one topologicaly clean
area (without overlaps) linked to 2 records (original attributes of
the 2 areas).  Those are the 2 tabs for Layer 1.

Because this happens quite often when a shapefile is imported
and in most cases it means errors (overlaps) in input data
v.in.ogr adds for convenience a new layer 2 with number
of categories in Layer 1. Using Layer 2 it is very easy
to visualize and identify all errors in the input data.

Radim

> g.list shows the vector name to be "test",
>
> v.info shows 1 dblink. and the -c option shows:
>
> GRASS 6.1.cvs (minnesota_utm):~ > v.info -c test
> Displaying column types/names for database connection of layer 1:
> INTEGER|cat
> INTEGER|id
> CHARACTER|type
> CHARACTER|class
> GRASS 6.1.cvs (minnesota_utm):~ >
>
> GRASS 6.1.cvs (minnesota_utm):~ > v.info -c test layer=2
> Displaying column types/names for database connection of layer 2:
> ERROR: Database connection not defined
>
> Any idea what might have happened? or how to get rid of the ghost
> layer1?
>
> Thanks,
>
> Kirk
>
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