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<p>Hello Frank:</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 2/7/19 3:16 PM, Frank David wrote:<br>
</div>
<blockquote type="cite"
cite="mid:837a3cc6-e041-e01b-14c4-b6f9b1ca9b8d@geophom.fr">
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<p>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.</p>
<p>Cheers,</p>
<p>Frank</p>
</blockquote>
<p><br>
</p>
<p>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.</p>
<p><br>
</p>
<p>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. </p>
<p><br>
</p>
<p>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. <br>
</p>
<p><br>
</p>
<p>If you are on Gitlab, you can clone the files: No documentation
yet :-(</p>
<p><a class="moz-txt-link-freetext" href="https://gitlab.com/tsvibar/route_viewshed">https://gitlab.com/tsvibar/route_viewshed</a></p>
<p><br>
</p>
<p>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.</p>
<p><br>
</p>
<p>Regards,</p>
<p>Micha<br>
</p>
<p><br>
</p>
<blockquote type="cite"
cite="mid:837a3cc6-e041-e01b-14c4-b6f9b1ca9b8d@geophom.fr">
<p> </p>
<div class="moz-cite-prefix">Le 07/02/2019 à 12:48, Frank David a
écrit :<br>
</div>
<blockquote type="cite"
cite="mid:ddec21d7-fbef-8a36-4f6f-a0f4a923814f@geophom.fr">
<meta http-equiv="Content-Type" content="text/html;
charset=UTF-8">
<p>Hi,</p>
<p>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.<br>
</p>
<p>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 !<br>
</p>
<p>I wondered if this kind of treatment exists already in Grass.
<br>
</p>
<p>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.</p>
<p>Sorry for my bad english, I hope you have understand my
wishes !<br>
</p>
<p>Cheers</p>
<p>Frank<br>
</p>
<div class="moz-cite-prefix">Le 07/02/2019 à 12:04, Veronica
Andreo a écrit :<br>
</div>
<blockquote type="cite"
cite="mid:CAAMki4FmyaxJo-NX_V177iBxnAsFkbOcfB-gbM-4r3UM0sjXvw@mail.gmail.com">
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charset=UTF-8">
<div dir="auto">Hi Ken,
<div dir="auto"><br>
</div>
<div dir="auto">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). </div>
<div dir="auto"><br>
</div>
<div dir="auto">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</div>
<div dir="auto"><br>
</div>
<div dir="auto">best,</div>
<div dir="auto">Vero</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr">El jue., 7 feb. 2019 07:16, Ken Mankoff <<a
href="mailto:mankoff@gmail.com" target="_blank"
rel="noreferrer" moz-do-not-send="true">mankoff@gmail.com</a>>
escribió:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">Hi
Frank,<br>
<br>
On 2019-02-07 at 08:27 +0100, Frank David <<a
href="mailto:frank.david@geophom.fr" rel="noreferrer
noreferrer" target="_blank" moz-do-not-send="true">frank.david@geophom.fr</a>><br>
wrote...<br>
> I try to find how to get the shifted minimum value of
a series of<br>
> raster map. I want to shift by one, or more, the
"minimum" value found<br>
> on each cell to get the "almost minimum" of the
series. Is there an<br>
> available function/method to do that ?<br>
<br>
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).<br>
<br>
-k.<br>
<br>
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<pre class="moz-signature" cols="72">--
Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918</pre>
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