[Qgis-user] Re: measure angle tool

[Giovanni Manghi]

"The aspect output raster map indicates the direction that slopes are
facing. The aspect categories represent the number degrees of east.
Category and color table files are also generated for the aspect map
layer. The aspect categories represent the number degrees of east and
they increase counterclockwise: 90deg is North, 180 is West, 270 is
South 360 is East. The aspect value 0 is used to indicate undefined
aspect in flat areas with slope=0."

http://grass.osgeo.org/grass64/manuals/html64_user/r.slope.aspect.html



On Tue, Aug 24, 2010 at 9:35 AM, ALT SHN <i.geografica at alt-shn.org> wrote:
>
>  don't know the answer but I have another question related to these one.
>
> Why is it when I use the aspect tool of GRASS (r.slope.aspect) the results
> are given from the East in a counterclockwise?! (i.e East is 0º, North is
> 90º and so on...)
>
> I only realized this because I always check the results, but I bet there are
> many people out there who assume that 360º/0º is North and are having
> inconsistent results....
>
> regards,
>
> Andre
>
> 2010/8/24 Tom <mtnbiketrail at zzz.com>
>>
>>  Why is it when I use the "Measure angle tool"(grouped with the "info"
>> tool), if I draw a line from 0 and then run the cursor around it a clockwise
>> circle, the measured value goes  0 to 180 and  -179 to -1 to 0, I want to
>> measure the obtuse angle like a compass, 0-360. nothing in the help files. I
>> have no clue if this is a built in plugin or add-in.
>>
>> Also, I can't seem to get the Azimuth and distance plugin tool(0.8.5) to
>> work.  I want to draw a line that is true North. NO instructions on their
>> website.
>>
>> And I'm using these to compare true north to magnetic north as
>> georeferenced raster files. The raster files are drawn to magnetic north,
>> with lines going to the 4 cardinal points as magnetic, but my base map
>> projection is in True North(+proj=utm +zone=10 +ellps=WGS84 +datum=WGS84
>> +units=m +no_defs). I want to georeference using magnetic bearings.  I know
>> the declination and the base map(geotiff) is correct.
>>
>> thanks,
>> Tom
>>
>>
>>
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>
>
>
> --
> ---------------------------------------------------------------
> Associação Leonel Trindade
> SOCIEDADE DE HISTÓRIA NATURAL
>
> Apartado 25 2564-909 Torres Vedras Portugal
> Sede e Biblioteca: rua Cavaleiros da Espora Dourada, 27A 2560 Torres Vedras
>
> Laboratório de Paleontologia e Paleoecologia: Polígono Industrial do Alto do
> Ameal 2565-641 Ramalhal
> http://alt-shn.blogspot.com
> www.alt-shn.org
>
>
>
> --
> ---------------------------------------------------------------
> Associação Leonel Trindade
> SOCIEDADE DE HISTÓRIA NATURAL
>
> Apartado 25 2564-909 Torres Vedras Portugal
> Sede e Biblioteca: rua Cavaleiros da Espora Dourada, 27A 2560 Torres Vedras
>
> Laboratório de Paleontologia e Paleoecologia: Polígono Industrial do Alto do
> Ameal 2565-641 Ramalhal
> http://alt-shn.blogspot.com
> www.alt-shn.org
>
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