[GRASS-dev] calculating bearing

[Michael Barton]

I'm doing a measure tool for wxgrass at the moment and realized that I have
the xy endpoints of each segment being passed to the MeasureDist method. If
there is an easy way to do so, it seems handy to add bearing to the output
along with segment length. Do you think that it is enough of a problem with
latlon regions that I shouldn't add it in?

Michael


On 5/16/07 1:40 AM, "Hamish" <hamish_nospam at yahoo.com> wrote:

> Michael Barton wrote:
>> 
>> Is there a simple formula to calculate bearing if you have the
>> beginning xy of a line and the ending xy of the line?
> 
> trig:  angle = atan(y/x)    [or atan2()]
> 
> see Glynn's warnings in the archives about that going undefined at places.
> 
> see also:
>   g.manual m.cogo
> 
> it gets ugly with lat/lon great circle calculations as the bearing isn't
> steady. (but there are map projections that help with that)
> 
> I've got some matlab functions for doing this if m.cogo isn't your cup
> of tea.
> 
> 
> Hamish

__________________________________________
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