[GRASS-dev] v.edit

[Michael Barton]

Jachym,

See below

Michael
__________________________________________
Michael Barton, Professor of Anthropology
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton



> From: Jachym Cepicky <jachym.cepicky at centrum.cz>
> Date: Tue, 6 Jun 2006 11:43:05 +0200
> To: Wolf Bergenheim <wolf+grass at bergenheim.net>
> Cc: GRASS developers list <grass-dev at grass.itc.it>
> Subject: Re: [GRASS-dev] v.edit
> 
> Hallo,
> 
> great work
> 
> On Tue, Jun 06, 2006 at 10:30:47AM +0300, Wolf Bergenheim wrote:
>> Ok now v.edit's add functionality is completed. One can add
>> point,line,area,boundary,centroid. Boundaries will not be given a cat.
>> 
>> Adding an area tries to put a centroid in the geographic mean, and if it
>> fails it will exit, with nothing added.
>> 
>> if you give many co-ordinates when adding a point many points will be
>> generated.
>> 
>> The cat support includes support for many cat's and ranges. This is for
>> instance supported:
>> v.edit map=test cat=267,347-350,353,356-359 coords=...
>> And if there are more points then given cats, the cat will just be
>> increased by one. The example above will result in 10 cats:
>> 267,347,348,349,350,353,356,357,358 and 359. If you give 11 point the
>> eleventh point will get the next cat (which is 360)
>> 
>> --Wolf
> 
> Why should a boundary NOT have category too? How would you distinguish
> two different types of boundary arround one area? Example on
> 
> http://les-ejk.cz/tmp/boundaries.gif
> 
> One country (Sachsen) has 2 different types of boundaries (country and
> state).

You can also think of this conceptually as 2 different areas (country and
state) that overlay. Or the area can simply have 2 attributes or even 2
layers (a state layer and a country layer). So there are a number of ways
to represent this situation.

As I said earlier, while it sometimes might be convenient for a boundary to
have a cat (with possibility of attributes) separate from that of an area, I
think it is better to make boundaries different from lines.

A line can be open or closed, has a cat and attributes. It is a vector
entity.

A boundary, while internally structured like a line, is part of a complex
entity called area. The complex area entity is composed of a closed line and
a point, and has a single cat for the closed line/point pair.

I think this kind of definition would make entity creation and management
easier than it is now. A boundary that is not part of an area and is not a
closed line is an odd, confusing entity IMHO. Could be convenient, I admit,
but I think that we are better off without it.

Michael
> 
> I thing, it is usefull to have a possibility for adding category number
> (and attributes) to boundary too.
> 
> Or do I understand it wrong?
> 
> Jachym
> 
> 
> --
> Jachym Cepicky
> e-mail: jachym.cepicky at centrum.cz
> URL: http://les-ejk.cz
> GPG: http://les-ejk.cz/gnupg_public_key/jachym_cepicky-gpg_public_key.asc
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