[postgis-users] Angle

[Arnaud Lesauvage]

Ezequias Rodrigues da Rocha wrote:
> Arnaud Lesauvage escreveu:
>> Ezequias Rodrigues da Rocha wrote:
>>> Arnaud Lesauvage escreveu:
>>>> Ezequias Rodrigues da Rocha wrote:
>>>>> Could someone tell me how to get an angle of a linestring feature ?
>>>>>
>>>>> Regards...
>>>>>
>>>>
>>>> The azimuth(geometry, geometry) function might be what you are 
>>>> looking for.
>>>> Input geometries are points, so you might use 
>>>> Azimuth(StartPoint(geometry), EndPoint(geometry)) if geometry is a 
>>>> Linestring.
>>>>
>>>> http://postgis.refractions.net/docs/ch06.html#id2528534
>>
>>
>> What do you think these "StartPoint" and "EndPoint" functions do ?
>> Have you read the documentation at http://postgis.refractions.net/docs/ ?
>> All you questions are answered there.
> Arnaud (great name. The name of my grandfather),
> 
> I tried like this but the result (as you can see now) is too below.
> 
> dbpotgis=# SELECT azimuth(startpoint(the_geom),endpoint(the_geom)) as 
> azimuth from mub where gid = 2900;
>      azimuth
> ------------------
>  2.17998093202836
> (1 row)
> 
> dbpotgis=#
> 
> The real angle is 143,9 and the function only rerutns 2.17...
> 
> Could you tell me what I did wrong ?


Azimtuh returns an angle in radians, you will need to convert that 
to degrees.
Then, I *believe* that azimuth is the angle measured from the 
North, so if you need an angle mesured form a west-east line you 
will have to add 90 degrees to that also.

--
Arnaud