[GRASS-user] Re: grass-user Digest, Vol 33, Issue 10

[Michael Barton]

On Jan 6, 2009, at 2:01 PM, <grass-user-request at lists.osgeo.org> wrote:

> Date: Tue, 6 Jan 2009 20:28:49 +0000 (GMT)
> From: Benjamin Ducke <benjamin.ducke at oxfordarch.co.uk>
> Subject: Re: [GRASS-user] v.centroids and cat values
> Cc: grass-user <grass-user at lists.osgeo.org>
> Message-ID:
> 	 
> <1559037892.138311231273729471.JavaMail.root at mail.thehumanjourney.net>
> Content-Type: text/plain; charset=utf-8
>
> GRASS modules that create area type features should already be  
> generating
> centroids and adding categories to them automatically, shouldn't they?

I don't know.

>
> As far as I am aware, e.g., v.in.ogr does this, so we are talking  
> mainly
> about adding centroid generation to the interactive digitizing tool,  
> aren't we?

In this case yes. I don't know about other modules.

>
> The GRASS Vector lib API should have a function that finds a good  
> centroid automatically.
> Or am I misled here (guess I am getting a bit confused myself, now)?

This is a good idea. If it exists, perhaps it should be accessed by  
the digitizing module as the default.

>
>
> To be quite honest, I have always been a bit bewildered about the  
> choice
> of using a centroid point for linking attributes to area features.
> Could anyone here fill me in on what advantage that has?

My bet is that is is a legacy of early GRASS vector design--a  
convenient way to create a polygon and give it some data. I still find  
it strange that a "boundary" can exist that is not a "line" and not a  
part of an "area".

Happy New Year to you too.
Michael