Hi,
On Mon, Nov 4, 2013 at 2:16 PM, Anna Petrášová <kratochanna@gmail.com>wrote:
Hi,
On Mon, Nov 4, 2013 at 1:36 PM, Rebecca Bennett <rabennett@ymail.com>wrote:
Dear GRASS users,
I have recently been made aware of the positive and negative openness
vizualisations (Yokoyama et al 2002
http://www.asprs.org/a/publications/pers/2002journal/march/2002_mar_257-265.pdf)
and would like to try to compute them in GRASS to help identify micro
relief.Though I suspect that this has already been done, I can't find a heads up
other than this paper (which claims to have creates the web service based
on GRASS here
http://geobrain.laits.gmu.edu/grassweb/manuals/raster/openness.html)http://www.lpi.usra.edu/science/stepinskiWebPage/pdfFiles/geoinformaticsConf2009.pdf
Just a note that although similar in it's aim of highlighting
microtopography, this is not quite the same as the r.horizon calculation
(image attached for clarification).All the best,
RebeccaI added recently a module r.skyview to grass 7 addons for computing the
sky-view factor [1]. It uses r.horizon module. I am not sure how much
different is what r.horizon can do and what you need but it's worth looking
if r.horizon cannot be extended easily and then used for the openness
computation.Anna
I attached a simple patch for r.horizon which enables to output also
negative elevation angles. Addon r.skyview can be then extended to compute
also openness besides the skyview factor (the difference is just the range
of elevation angles if I understood correctly). It looks like the negative
openness can be then computed in the same way, but with inverted elevation.
Regards,
Anna
[1] https://svn.osgeo.org/grass/grass-addons/grass7/raster/r.skyview/
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