[GRASSLIST:1499] RE: bearing/angle

[Dan Gelinas]

Not sure if a COGO (coordinate Geometry) module is available for grass. It probably wouldn't be hard to add this to grass using c.
The manual way to calculate bearing/angle is the following:
Known information: Eastings/Northing x/y coordinates of your two points, for example, based on the first quadrant:
a = 1.5, 1.4
b = 4.1, 3.4

Distance ab is calculated:
dx = xb - xa = 4.1 - 1.5 = 2.6
dy = yb - ya = 3.4 - 1.4 = 2.0
ab = sqrt(sqr2.6 + sqr2.0) = 3.28

Azimuth (@) is calculated as such:
@AB = arc tg 2.6/2.0 = 52o26'

All other quadrants:
First Quad:   dx:+  dy:+
Second Quad:  dx:+  dy:-
third Quad:   dx:-  dy:-
Forth Quad:   dx:-  dy:+ 

-Daniel
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-----Original Message-----
From: Christian G. Tveen [mailto:cgt at navicon.dk]
Sent: Wednesday, October 15, 2003 3:41 AM
To: GRASSLIST at baylor.edu
Subject: [GRASSLIST:1496] bearing/angle


Hello,



I need a way to calculate the bearing / angle between two points. To be 
more precise, I need to know in what direction and how long to go from 
one point to get to the other. I use the distance functionality to 
calculate 'how long to go' but need the direction. Is there any 
functions to do so ?  If this is not sufficient information, pls. don't 
hesitate asking me.


Regards

Christian G. Tveen