Re: [GRASS-user] calculation valley floor width in GRASS or some index indicating valley floor width?
SBL wrote Hei Helumt, In that case I would probably try r.param.scale in order to identify flat areas at maybe different scale levels. V-valleys have a higher variation in aspect at the bottom (sides are almost facing each other and nearly meet at the lowest point in a V-valley). While sides are more or less steep. So slope and aspect at a coarser level (also available through r.param.scale) could help to distinguish V- and U-valleys. Depending on scale U-Valleys have a TPI of ~0 at the bottom and ~0 at the middle of the sides (equaly much terrain above and below a focal cell in the given neighborhood). Some background material on TPI can be found here: http://www.jennessent.com/arcview/tpi.htm Jenness used ArcView. Yet TPI is a simple combination of r.neighbors and a mapcalc. Good luck with your modelling. as a possible additional parameter for such a modelling, I've tried to implement a Multi-resolution Valley Bottom Flatness (MrVBF) index. http://lists.osgeo.org/pipermail/grass-commit/2014-June/031834.html Author: hellik Date: 2014-06-22 16:04:15 -0700 (Sun, 22 Jun 2014) New Revision: 60919 Added: grass-addons/grass7/raster/r.valley.bottom/ grass-addons/grass7/raster/r.valley.bottom/Makefile grass-addons/grass7/raster/r.valley.bottom/r.valley.bottom.html grass-addons/grass7/raster/r.valley.bottom/r.valley.bottom.py Log: r.valley.bottom: a script to calculate a Multi-resolution Valley Bottom Flatness (MrVBF) index testing and hints for improvement are very welcome. thanks - best regards Helmut -- View this message in context: http://osgeo-org.1560.x6.nabble.com/calculation-valley-floor-width-in-GRASS-or-some-index-indicating-valley-floor-width-tp5132402p5147233.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] calculation valley floor width in GRASS or some index indicating valley floor width?
Hi Helmut, After a second thought on this, personally, (given that I understood your aim correctly) I would probably use a workflow like: r.watershed in order to extract the streams (which are not unlikely to meander or split up into different courses in wider U-valleys) r.stream.distance in order to extract the elevation above stream r.param.scale (probably with different neighborhood sizes) for identifying flat areas and valley sides (based on the elevation above stream raster) r.mapcalc for modeling the bottom of the valley as flat areas (slope threshold) below an elevation threshold above the stream r.reclass.area for removing some unwanted islands r.mapcalc for inverting the valley bottom map (valley bottom = NoData, rest = 1) r.grow.distance for measuring the distance from the inverted valley bottom r.neighbors for measuring the maximum distance within one (or more) neighborhood(s) - depending on expected maximum valley width - as an estimate on total valley width. Cheers Stefan ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] calculation valley floor width in GRASS or some index indicating valley floor width?
On Tue, 1 Apr 2014 00:52:53 -0700 (PDT) Helmut Kudrnovsky hel...@web.de wrote: hi, any hint or pointer to some grass gis procedure/literature/web link/etc how to caculate valley floor width in GRASS or some index indicating valley floor width. the idea is to get some measure how wide or narrow a valley is. thanks in advance! That is a very involved question, starting with how you define the valley floor quantitatively to begin with. You could calculate an index of concavity or average slope and plot the point where the measure (e.g. concavity of slope, or average slope) drops below a certain value that would be a valley floor boundary by definition. There should be several grass tools that could be applied. JWDougherty ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] calculation valley floor width in GRASS or some index indicating valley floor width?
Helmut wrote: any hint or pointer to some grass gis procedure/literature/web link/etc how to caculate valley floor width in GRASS or some index indicating valley floor width. the idea is to get some measure how wide or narrow a valley is. JWDougherty wrote: That is a very involved question, starting with how you define the valley floor quantitatively to begin with. You could calculate an index of concavity or average slope and plot the point where the measure (e.g. concavity of slope, or average slope) drops below a certain value that would be a valley floor boundary by definition. There should be several grass tools that could be applied. e.g. run 'r.param.scale param=feature' to pull out channels, then r.watershed to make a rivers map and r.cost to calculate distance from the center-line (rivers) to the edge of the valley. Of course rivers are not always in the center of the valley, perhaps take the r.param.scale valleys and run r.cost to find the cost to the middle. Then extract the 'ridge lines' of the distance-cost map, again with r.param.scale, and double the peak values along the ridge. It is very similar to the classic 'river mile' problem, to define well a line down the center of the channel when nature isn't as simple as a pipe and valleys merge, islands happen, etc. Hamish ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] calculation valley floor width in GRASS or some index indicating valley floor width?
Hei Helumt, I guess the main challenge is how to define (or delimit) the valleys (and especially the valley-floor)... If you think of valleys in a hydrological perspective I would have a look at r.stream. modules for having a kind of threshold above streams (in m), and then use r.grow.distance for an inverted valley representation. If you think of valleys in a geomorphometric context things might be a bit more complex (esp. for U-valleys, compared to V-valleys). A colleague of mine (and to some degree myself too) has been working on a valley map for Norway quite intensively (http://www.nhm.uio.no/forskning/publikasjoner/rapporter/nhm-rapport-11-faglig-grunnlag-for-naturtypeovervaaking-grunnlagsundersoekelser.pdf (pages 99 following, text in Norwegian, map at page 104) and still there are reasonable challenges left in order to properly define valley extents, even though my colleague improved the procedure to a 2.0 version of the valley algorithm. Depends how much effort you like to or can spend on that... In a geomorphometric context r.geomorphon, r.param.scale, or more general Topographic Position Index (TPI) might be worth having a look at. Please note that all these three are heavily scale dependent! Cheers Stefan -Original Message- From: grass-user-boun...@lists.osgeo.org [mailto:grass-user-boun...@lists.osgeo.org] On Behalf Of Helmut Kudrnovsky Sent: 1. april 2014 09:53 To: grass-user@lists.osgeo.org Subject: [GRASS-user] calculation valley floor width in GRASS or some index indicating valley floor width? hi, any hint or pointer to some grass gis procedure/literature/web link/etc how to caculate valley floor width in GRASS or some index indicating valley floor width. the idea is to get some measure how wide or narrow a valley is. thanks in advance! - best regards Helmut -- View this message in context: http://osgeo-org.1560.x6.nabble.com/calculation-valley-floor-width-in-GRASS-or-some-index-indicating-valley-floor-width-tp5132402.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] calculation valley floor width in GRASS or some index indicating valley floor width?
Hi Stefan, thanks your response. If you think of valleys in a hydrological perspective I would have a look at r.stream. modules for having a kind of threshold above streams (in m), and then use r.grow.distance for an inverted valley representation. If you think of valleys in a geomorphometric context things might be a bit more complex (esp. for U-valleys, compared to V-valleys). it's maybe a mixing of both... ;-) given is a habitat typical for gravel beds/braided river in mountain regions. it seems the probability of the occurrence of the needed habitat structure is greater in wider valleys floors than in narrow valley floors, and greater in U-valleys than in V-valleys. the idea is to get some measure/index to handle this probability ... - best regards Helmut -- View this message in context: http://osgeo-org.1560.x6.nabble.com/calculation-valley-floor-width-in-GRASS-or-some-index-indicating-valley-floor-width-tp5132402p5132410.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] calculation valley floor width in GRASS or some index indicating valley floor width?
Hei Helumt, In that case I would probably try r.param.scale in order to identify flat areas at maybe different scale levels. V-valleys have a higher variation in aspect at the bottom (sides are almost facing each other and nearly meet at the lowest point in a V-valley). While sides are more or less steep. So slope and aspect at a coarser level (also available through r.param.scale) could help to distinguish V- and U-valleys. Depending on scale U-Valleys have a TPI of ~0 at the bottom and ~0 at the middle of the sides (equaly much terrain above and below a focal cell in the given neighborhood). Some background material on TPI can be found here: http://www.jennessent.com/arcview/tpi.htm Jenness used ArcView. Yet TPI is a simple combination of r.neighbors and a mapcalc. Good luck with your modelling. Cheers, Stefan -Original Message- From: grass-user-boun...@lists.osgeo.org [mailto:grass-user-boun...@lists.osgeo.org] On Behalf Of Helmut Kudrnovsky Sent: 1. april 2014 10:33 To: grass-user@lists.osgeo.org Subject: Re: [GRASS-user] calculation valley floor width in GRASS or some index indicating valley floor width? Hi Stefan, thanks your response. If you think of valleys in a hydrological perspective I would have a look at r.stream. modules for having a kind of threshold above streams (in m), and then use r.grow.distance for an inverted valley representation. If you think of valleys in a geomorphometric context things might be a bit more complex (esp. for U-valleys, compared to V-valleys). it's maybe a mixing of both... ;-) given is a habitat typical for gravel beds/braided river in mountain regions. it seems the probability of the occurrence of the needed habitat structure is greater in wider valleys floors than in narrow valley floors, and greater in U-valleys than in V-valleys. the idea is to get some measure/index to handle this probability ... - best regards Helmut -- View this message in context: http://osgeo-org.1560.x6.nabble.com/calculation-valley-floor-width-in-GRASS-or-some-index-indicating-valley-floor-width-tp5132402p5132410.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
