On 2/16/19 12:00 PM, Frank David wrote:
Hi Micha,
Thank you for your email. Your script is very interesting, but
I think I cannot use it because:
1- you make a sum of your viewshed list, and each viewshed
value is 0 or 1 (hidden or visible). But my problem is with
viewshed values from 0 upto 250 (for each viewshed this is the
hidden height from a viewpoint). So make a sum has no sens.
2- you search the pourcent of visible terrain from all
viewpoints, and I want find pourcent of viewpoints able to see
terrain (actually to not see the maximum hidden height above
terrain)
Tell me if I'm wrong...
You're right. That is my understanding also.
What I was thinking was to use the "max_overlap" parameter to
find all areas in the search radius that are visible by at most
i.e. 80% of the viewsheds. Then invert that raster - wherever
there is some value, set to NULL, and wherever the value is NULL
set to the DTM elevation (+ turbine height). That will give you
the height at all pixels that are not visible from 20% of the
viewsheds.
In any case it's an interesting application.
I wrote a script with garray.array() which read the value for
each specific x,y cell coordinates from all viewshed rasters,
create a list of data, sort that list, and get the shifted min
(according to my tolerance, for example 80% of 100 viewpoints
get the twentieth smallest value). In that way Each cell of my
output raster give the hidden height from 80% of my viewpoints.
The script is working, but I believe that adding this function
in r.series could be useful.
Cheers,
Frank
Le 15/02/2019 à 15:52, Micha Silver a
écrit :
Hello Frank:
On 2/7/19 3:16 PM, Frank David
wrote:
I forgot one thing to well understand my wish. Each
viewshed raster is a r.series (250-sum) of 250 r.viewshed
with 2m target and 0 upto 250m terrain height. So each
raster gives the hidden height of a building (250m max)
anywhere on the region from a specific point of view. The
purpose is to get the area of hidden wind turbine from roads
for a specific wind turbine height.
Cheers,
Frank
A friend and I were working on an idea some months ago that
might be of interest. Not the same as your project but the
method I used is similar.
The search and rescue teams here are interested to see what
areas were actually visible after they finish searching along
a certain route, and what areas were not seen at all. I used
the same approach as you, creating a series of overlapping
r.viewshed intermediate rasters.
After seeing your post, I have added new input parameters for
minimum and maximum values of overlap. The user can enter
percents of minimum or maximum viewshed overlaps. Suppose I
put in 20 as the minimum, then only those pixels with at least
20% of the total number of viewsheds will be shown. Similarly,
if I enter 80 as the maximum, then only those pixels with less
than 80% of the maximum number of viewsheds will appear in the
final raster.
If you are on Gitlab, you can clone the files: No
documentation yet :-(
https://gitlab.com/tsvibar/route_viewshed
If you do adopt any of this script, I'd appreciate to hear of
any bugs or suggestions for improvement. If the script raises
any interest, I'll add it to the Addons.
Regards,
Micha
Le 07/02/2019 à 12:48, Frank
David a écrit :
Hi,
Thanks for your reply. I can have numerous raster
(several hundreds). I want to find a minimum but with a
tolerance, it's why I want to be able to shift the value.
In fact I want to sort the value of my all input raster
for each x,y cell and get the second or third, or any
position in the sorted list, to build my output raster. My
application is to get the area not visible from a road (I
did 1600 viewshed raster from the roads every 250m). I
want a tolerance in order that one point of view (top of
hill) does not reduce too much the hidden area. To do so,
a fixed number of my point of view (20%) does not reduce
the hidden area. The result is the area is hidden from 80%
of the road.
I already wrote a python script that read all rasters for
each x,y cell and make a array(), sort the array values,
and build a raster. It works on reasonable number of cell,
but seems to fails with large number of cells. I'm not a
programmer !
I wondered if this kind of treatment exists already in
Grass.
If somebody wants to hemps me to develop this, I could be
nice. But I think it could be an improvement of r.series
function.
Sorry for my bad english, I hope you have understand my
wishes !
Cheers
Frank
Le 07/02/2019 à 12:04, Veronica
Andreo a écrit :
Hi Ken,
There isn't any build-in function for
that in grass, afaik. Depending on how long is your
series, you could shift the map list you use in each
run and then use r.univar on each output from r.series
to get the minimum and by comparison, get the second
minimum of the series of maps (a scalar).
However, if what you need is a map of
second minimums per pixel, I believe that might
require some programming for a new function... Do you
know any other software which has this function?
Maybe, if there's such thing in Python for example, it
could be recycled or used with grass maps in a
script... Dunno, just thinking out loud
best,
Vero
Hi
Frank,
On 2019-02-07 at 08:27 +0100, Frank David <frank.da...@geophom.fr>
wrote...
> I try to find how to get the shifted minimum
value of a series of
> raster map. I want to shift by one, or more, the
"minimum" value found
> on each cell to get the "almost minimum" of the
series. Is there an
> available function/method to do that ?
I don't think I fully understand what you want. Are
you working with strds? You mention "series". If I
wanted to get the second-minimum of a single raster, I
would use r.stats with the "-1" flag, sort, and search
for the 2nd (or 2nd-to-last).
-k.
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--
Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918
--
Geophom
327 rue de Vieille Cour 44521 OUDON
Tel +33(0)2 85 52 02 59 - Port +33(0)6 04 47 91 06
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Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918
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