[GRASSLIST:348] Re: using v.patch

[Paul Kelly]

Hello Michele

On Wed, 11 Jun 2003, [iso-8859-1] michele.rocc wrote:

> Hi all grass users,
>
> I have to patch several vector file:
>
> first I imported files from dxf files with v.in.dxf and v.in.dxf3d
> then rebuild category file with v.support for every imported layer.
> At this point I want to build a single layer using v.pacth, all seems to run Ok
> but I get this
>
> WARNING: category support for vector file [vect.file1] in mapset [pce1]  missing
>
> is this only a reminder to tell that v.support have to be run again on new patched file or
> did something go wrong with initial rebuilding of category file?

This would be because v.in.dxf and v.in.dxf3d don't create a category
file (dig_cats); they store all the categories in the attributes file
(dig_att). If the categories are all positive integer numbers (e.g.
contours above sea level) this is probably all right and nothing much to
worry about then.

And if they are contours then it will even be useful when you are
running v.patch as the contours in the different files with the same value
will have the same attribute number and they will all patch together
cleanly.

But if you have positive floating point numbers v.support will truncate
them to integers, and it will delete any other categories (e.g. zero or
text values). It does this without warning.

With help from John Gillette I had prepared a patch for v.in.dxf and
v.in.dxf3d so it would put a unique number in the dig_att file for each
category and write the category to the dig_cats file. But I didn't apply
it to GRASS as I wasn't sure this was the best way of solving the problem.
For example, it would mess up the output of v.patch as the same attribute
number might correspond to different categories in the different input
files.

In short, if your DXF files contain contours and there were no 0 or
negative values, it should be OK.

Paul