[GRASSLIST:7828] Re: azimuth of a line

[David Finlayson]

I'm not sure exactly what you need. But this might help.

1) Convert the nodes of your coverage to points using v.to.points
(format=point option)

2) Dump the points as an ascii text stream using v.to.ascii and pipe
the results into a
script that calculates the azimuth.

I have written a small python utility that calculates the distance and
azimuth along a list of points:

http://students.washington.edu/dfinlays/scripts/cogop.py  

Here is an example of how it can be used. I have a polygon called
trimpoly. I convert it to a list of points using v.to.points:

GRASS 6.1.cvs (UTM10_NAD83): > v.to.points -v input=trimpoly output=trimpolypts
Building topology ...
20 primitives registered
Building areas:  100%
0 areas built
0 isles built
Attaching islands:
Attaching centroids:  100%
Topology was built.
Number of nodes     :   19
Number of primitives:   20
Number of points    :   20
Number of lines     :   0
Number of boundaries:   0
Number of centroids :   0
Number of areas     :   0
Number of isles     :   0
20 points written to output map

Now I can dump this point file as ascii text:

> v.out.ascii input=trimpolypts
536022.25|5332267.25|-1
536029.98|5332292.26|-1
536041|5332314.36|-1
536066.78|5332355.57|-1
536081.01|5332349.24|-1
536098.13|5332341.62|-1
...

We can get rid of the pipe characters and replace them with tabs with
sed and then
pipe the result to my cogop.py script like this:

> v.out.ascii input=trimpolypts | sed 's/|/\t/g' | cogop -a
0.0  536022.25 5332267.25 -1
26.18 17.18 536029.98 5332292.26 -1
24.7 26.5 536041 5332314.36 -1
48.61 32.03 536066.78 5332355.57 -1
15.57 113.98 536081.01 5332349.24 -1
18.74 113.99 536098.13 5332341.62 -1

The first column is the distance between points, the second column is
the azimuth from point 1 to point 2, finally, the script appends the
input fields. cogop has a few other options like setting a benchmark
and calculating cumulative distance, etc. Of course the order of the
points is important.

Hope that gives you some ideas,

David


On 8/8/05, Carlos Guâno Grohmann <carlos.grohmann at gmail.com> wrote:
> I was wondering if v.to.db could have a "azimuth" option, to calculate
> the azimuth of line segments, based on the end vertices coordinates.
> 
> Carlos
> --
> +-----------------------------------------------------------+
>               Carlos Henrique Grohmann - Guano
>   Geologist M.Sc  - Doctorate Student at IGc-USP - Brazil
> Linux User #89721  - carlos dot grohmann at gmail dot com
> +-----------------------------------------------------------+
> 
> 


-- 
David Finlayson
Marine Geology & Geophysics
School of Oceanography
Box 357940
University of Washington
Seattle, WA  98195-7940
USA

Office: Marine Sciences Building, Room 112
Phone: (206) 616-9407
Web: http://students.washington.edu/dfinlays