[GRASS-user] creating new geometry from pre-existing lines and points

[Nikos Alexandris]

Hi!

On Wed, 2008-01-30 at 23:52 +0200, David Epstein wrote:
> Hi Nikos,
> 
> Thank you for that suggestion. Indeed, I did NOT realize that v.extract
> was used to create new geometry in a layer. However, I too need some of
> the islands (is there a technical difference between island, hole, and
> missing polygon?).

I am not sure!

Would be nice to have a kind of GRASS-GIS lexicon with (basic and
non-basic) definitions!

* island... I suppose are small poylgons within larger ones

* holes... just "nothing" within larger polygons

* missing polygon... ?

> 
> There is a single missing polygon that I now have attribute data for and
> I want to create the polygon (from the existing points and lines) and
> fill-in the related attribute fields.
> 
> I imagined some sort of interactive process of clicking on the relevant
> bounding elements and *presto* the polygon would jump into existence. I
> tried this in v.digit but was not able to get the desired result.

If you just need to quickly correct a small number of polygons try with
the "fresh-baked" QGIS (r0.9.2.rc1), which works as a GRASS frontend.

1. you need to add in your /etc/apt/sources.list following source:
deb http://ppa.launchpad.net/timlinux/ubuntu gutsy main

2. sudo aptitude update && sudo aptitude upgrade

--- if not already installed... "sudo apt-get install qgis
qgis-plugin-grass"---

3. Load GRASS plugin

4. Open your GRASS mapset within QGIS

5. Load your vector (polygon) file

6. Play with the tools... ( I have seen the new digitising tools... must
be really what you are looking for!) and edit your polygons.

*** You need first to "right click" on your vector layer and "save as
shapefile" -- Then you can edit.



> 
> This is a really basic step that people do several times a day, right?
> 
> -david
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