[gdal-dev] gdal_viewshed

[Eli Adam]

Hi Pedro,

On Thu, May 7, 2020 at 4:03 PM Pedro Venâncio <pedrongvenancio at gmail.com> wrote:
>
> Hi,
>
> I'm trying the new gdal_viewshed and it is in fact really quick! But the result is completely different than other viewshed analysis algorithms:
>
> https://cld.pt/dl/download/e80216bb-d7eb-40b0-b6da-8e45572e9eb3/viewshed.jpg
>
> https://cld.pt/dl/download/ee993a0b-cf86-462a-b831-307aecde7865/viewshed2.jpg
>
> GRASS and Visibility Analysis plugin for QGIS have almost the same result. The result from gdal_viewshed seems completely overrated. The options I'm using are [almost] the same in both algorithms.
>
> gdal_viewshed -b 1 -md 28000.0 -ox -41597.922 -oy 71254.049 -oz 21.6 -tz 10.0 -vv 1 -cc 0.85714 -f GTiff path_to_mdt.tif path_to_output.tif
>

Does -tz 10.0 in effect raise your DEM target elevation by 10 units?
Was the same done in GRASS and the Visibility Analysis plugin for
QGIS?

Was the observer height of -oz 21.6 the same for all three as well?

Best regards, Eli

> Has anyone else this experience?
>
> Thanks! Best regards,
> Pedro Venâncio
>
>
> Howard Butler <howard at hobu.co> escreveu no dia quinta, 7/05/2020 à(s) 17:41:
>>
>>
>>
>> > On May 7, 2020, at 11:05 AM, Eli Adam <eadam at co.lincoln.or.us> wrote:
>> >
>> > The image with two dots makes me think that there can be multiple
>> > observer inputs.  Is that the case?  Is the syntax for that just to
>> > keep adding more -ox, -oy, (and oz)?  For instance, gdal_viewshed -md
>> > 500 -ox -10147017 -oy 5108065 -ox -10147117 -oy 5108165+100 source.tif
>> > destination.tif
>>
>> The picture is a poor example. You can't do multiple obvservers, but you can run a bunch of masks together and then merge to get a multipoint viewshed. I indeed made two masks with gdal_viewshed and then merged them together to make that picture.
>>
>> That picture or the docs should maybe be updated to reflect a more common scenario with better description. File a ticket and attach some language and pictures to it as you start playing with it and we can merge it.
>>
>> Thanks,
>>
>> Howard
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>
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-- 
Eli L Adam, PLS
Lincoln County Surveyor's Office
880 NE 7th Street
Newport, OR 97365
541-574-1289