[GRASS-user] raster analysis sectorwise as in a pie chart

GRASS GRASS user
1

Hi,

I would like to analyse elevation data (slope, aspect, etc) around a point with
a defined radius. For my analysis I would like to devide that circle into
several sectors 1,5,10,x degree steps, like a pie.

Is that possible in GRASS? Are there people who did something similar? Any hints
and ideas are welcome.

regards,
Otto

2

Otto Dassau wrote:

I would like to analyse elevation data (slope, aspect, etc) around a
point with a defined radius. For my analysis I would like to devide
that circle into several sectors 1,5,10,x degree steps, like a pie.

Is that possible in GRASS? Are there people who did
something similar? Any hints and ideas are welcome.

r.reclass into range bands, then

d.histogram style=pie (perhaps rendered into a corner sub- d.frame)

or somehow into a vector DB + 'd.vect.chart ctype=pie'

Hamish

3

On Tue, 27 Jan 2009 15:46:02 -0800 (PST)
Hamish <hamish_b@yahoo.com> wrote:

Otto Dassau wrote:
> I would like to analyse elevation data (slope, aspect, etc) around a
> point with a defined radius. For my analysis I would like to devide
> that circle into several sectors 1,5,10,x degree steps, like a pie.
>
> Is that possible in GRASS? Are there people who did
> something similar? Any hints and ideas are welcome.

r.reclass into range bands, then
d.histogram style=pie (perhaps rendered into a corner sub- d.frame)
or somehow into a vector DB + 'd.vect.chart ctype=pie'

thanks for your suggestion, but maybe my description was not very clear. I would
like to split data into spatial sectors and then start my analysis. E.g.:

a) Create a 1km buffer around a coordinate
b) Split this circle into sections (subareas) with a certain degree value. If I
choose 1 degree the circle would be devided into 360 subareas
c) Do my analysis in each sector

I am thinking about a solution for b)

regards,
Otto

4

On Wed, Jan 28, 2009 at 10:40 AM, Otto Dassau <otto.dassau@gmx.de> wrote:

On Tue, 27 Jan 2009 15:46:02 -0800 (PST)
Hamish <hamish_b@yahoo.com> wrote:

Otto Dassau wrote:
> I would like to analyse elevation data (slope, aspect, etc) around a
> point with a defined radius. For my analysis I would like to devide
> that circle into several sectors 1,5,10,x degree steps, like a pie.
>
> Is that possible in GRASS? Are there people who did
> something similar? Any hints and ideas are welcome.

r.reclass into range bands, then
d.histogram style=pie (perhaps rendered into a corner sub- d.frame)
or somehow into a vector DB + 'd.vect.chart ctype=pie'

thanks for your suggestion, but maybe my description was not very clear. I would
like to split data into spatial sectors and then start my analysis. E.g.:

a) Create a 1km buffer around a coordinate
b) Split this circle into sections (subareas) with a certain degree value. If I
choose 1 degree the circle would be devided into 360 subareas
c) Do my analysis in each sector

I am thinking about a solution for b)

With v.buffer you can create a circle. Then with a bit of geometry [1] you
can calculate the angles and more (perhaps implement in a shell/python
script) and then generate the lines and centroids with v.edit.
Finally rebuild the topology to obtain sector areas (v.build).

Hope this helps,
Markus

[1] essentially, radius of circle, angle, school geometry :slight_smile: