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7

In spatial hydrology, DEM-based flow accumulation operations are typically static. That is, they represent a steady-state condition of the discharge of surface and near surface water passing through a point. Flow accumulation grids are actually accumulating contributing area downslope, i.e. areas not volumes. The accumulated cells that you described is ...


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What about using r.watershed with the flow input parameter? r.watershed elevation="elevation" flow="runoff" accumulation="flow_accumulation" ... For the flow input you need to provide a raster map representing amount of overland flow per cell. For a simplified approach assuming no groundwater flow etc. you can use your generated runoff map ...


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The very first thing you need is a slope raster, which is created from a DEM - see 8.3.3 here. To solve the first part of your problem, the average slope, you need a zonal statistics tool. This provides statistics of one raster's cell values based on areas defined by polygons or cells of constant value in another raster. There is a QGIS Zonal Statistics ...


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The best way to calculate several statistics for your raster layer is to use Focal Statistics from Spatial Analyst provided by ArcGIS!


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The regionsize is about 5x5 km. Your Idea is also a verry good one but for my Bachelorthesis i have to do it as i told. Maybe my method is better understood when I point my entire Process here: I also tried v.segment and v.to.points. But i canĀ“t choose a equidistant Distance between Points with that. So is there no other way?


1

There are two GRASS modules for creating a set of points from a line vector: v.to.points or v.segment. The first will extract all the existing nodes from the line, and will stick in extra points if two nodes are more distant than dmax parameter. The second allows more accurate control over the exact locations of the points. See the manual pages for better ...


3

I believe the general outline (partly tested so far) is: Find the points representing stream sources, as in this answer. Intersect with the polygons table to get a count of source vertices by polygon. Use ST_DumpPoints in conjunction with group by geometry to get a count of each point. The idea being to get a count of how many rivers meet at a given point. ...


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Thank you this is a good approach. My Idea was to create specific Points (e.g. each 50 meters), paste them into an attribute table (v.to.db) and then convert them to an csv file (with v.out.ascii). Next step is to loop the r.water.outlet (example: How to do the loop when using GRASS module r.water.outlet?) for each point by using csv file. However, I have my ...


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Giacomo had it right: QGIS SAGA Channel network error: Input layers do not have the same grid extent Alter extent of one of the layers to the other (in QGIS save layer as)... and the tool works.


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In pseudo code, this should work: select all from polygons (FULL OUTER?) join with points on polygon intersects points (FULL OUTER?) join lines where polygon intersects lines were line.riverid doesn't equal point.riverid group by polygonid count (pointid) > 0 I'm not really sure how to build the query, and I can't test it without a database to test on. ...



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