15
votes
Accepted
Calculate slope of line segments with QGIS
In the QGIS Processing Toolbox, there are GRASS tools v.split.length and v.drape (using QGIS 2.18.16).
Before starting;
0.) make sure your DEM and road data are projected onto the same CRS.
Then, ...
- 29.9k
13
votes
Slope, in which direction?
The direction of a Slope is known as its Aspect. It's usually defined as the direction the slope "faces", to me that's a little ambiguous and it's more intuitive to think of it as the "downhill" ...
- 12.1k
13
votes
Hillshade shows grid texture artifacts
The problem is because the DTM has a high-resolution pixel size when data (in my opinion) doesn't have the same resolution is some areas.
For example, direct hillshade raster:
Check pixel values (...
- 12.9k
12
votes
How to perform a slope analysis in QGIS?
Slope analysis is performed on a DEM (raster layer with elevation values). This is one way to do it. If your contours have an elevation value, you can use the interpolation option (raster/...
- 2,952
12
votes
Accepted
What is the default unit for slope in QGIS?
If you create a slope layer from Raster > Terrain Analysis > Slope, the output layer will have degrees as units of measurement.
Instead, using the Slope GDAL tool from the Processing Toolbox will ...
- 15.9k
12
votes
Calculate slope of line segments with QGIS
This is a modification of Kazuhito's answer using native QGIS algorithms using QGIS 3.12.
In the QGIS Processing Toolbox, there are the tools Split lines by maximum length and Drape (set Z value from ...
- 2,099
10
votes
Accepted
Getting incorrect slope values from an ASTER DEM in QGIS?
Aster DEMs are in EPSG 4326 (lat lon WGS84). According to the GDAL DEM documentation:
For LatLong projections near the equator, where units of latitude and units of
longitude are similar, ...
- 2,952
10
votes
Accepted
Average Cross Slope Calculation
Contours do not cross each other, so I cannot explain it using your example. Instead, let me illustrate what this ACS does by a picture below.
Looking at the pictures [1] and [2], you will find steep ...
- 29.9k
9
votes
Accepted
Calculating average stream slope at each location along stream using ArcGIS Desktop?
As @Hornbydd pointed it is network searching problem. I suggest the following workflow:
find source points of the streams
sort them in descending order by flow length
In the picture below 139 green ...
- 22.2k
9
votes
Accepted
Finding pixels in DEM with 5% slope or less?
You mention 3D Analyst so I am assuming you have ArcGIS.
Use the tool ArcToolbox-3D Analyst Tools-Raster Surface-Slope to create a slope surface from your LiDAR data.
Use the tool ArcToolbox-3D ...
- 8,502
9
votes
How to get the slope from an elevation raster in QGIS?
It looks like you are not using a digital elevation model (DEM) data. It is just an image (scanned image) from layout or something and not a real elevation data. You need to use elevation data such as ...
- 39.1k
8
votes
Accepted
Strange output from RSAGA topographic wetness index?
I think I see the problem.
I could reproduce this, both using your script, and SAGA itself. The output from SAGA matches the output from your script. So it's not RSAGA.
But look at the slope output ...
- 20.1k
8
votes
Accepted
Using SRTM DEM with 16 bit signed pixel type changes to 32 bit float when creating slope/aspect/curvature?
Each of the outputs that you described (slope, aspect, and curvature) are terrain attributes that are naturally described as rational numbers. As such, you would expect that the outputs of these tools ...
- 10.9k
8
votes
Calculating slope direction in QGIS?
I found tool for this. That is Saga plugin called: Gradient vector from surface.
And result is: you have to choose in style manager, arrow for lines
- 2,365
8
votes
Accepted
Rotating symbols per attribute value in QGIS?
If you want to use a field in attribute table, you should select the field directly in the Data defined override which has the angle value. The field should be of double/integer type not string field ...
- 39.1k
7
votes
Calculating relative share of an area of circle that has slope >15% in Germany
Doing this kind of processing is pretty straight-forward, but there are some tricks along the way that will determine how accurate your analysis will be. Your data will be generated from a slope ...
- 3,071
7
votes
Accepted
Calculating slope direction in QGIS?
You can generate the slope in several ways:
Raster -> Analysis -> DEM -> Slope. Or via slope functions in the Processing framework (r.slope.aspect). Run it on your DEM. Do the same for the aspect.
...
- 4,186
7
votes
Accepted
Conditional Statement (CASE-WHEN) in QGIS for slope aspect
If the Aspect raster converted to polygon or you have a shapefile with "Aspect" field name in the attribute table and you need to put the text definition, then you are almost there, but you need to ...
- 39.1k
7
votes
Prevent SAGA in QGIS 3.0 from creating certain outputs?
Should be possible to do if you feel like hacking your qgis install.
look for this file in your qgis install: https://github.com/qgis/QGIS/blob/master/python/plugins/processing/algs/saga/description/...
- 27k
7
votes
QGIS slope output problems
The herringbone pattern in your image is a classic indication that a Nearest Neighbor resampling occurred somewhere in your workflow. I suggest that you go back through each processing step and ...
- 7,475
6
votes
Accepted
Calculate slope of line based off of point layer
Join the points to the lines, using a spatial or table join, to give the elevation (Z) at each end of the line. This allows you to calculate the elevation change (Z1 - Z2). Use your GIS to calculate ...
- 20.8k
6
votes
Accepted
Calculating relative share of an area of circle that has slope >15% in Germany
You can download a European-wide DTM from the European Environmental Agency
Or use other open DTMs of Germany like this
As your calculations are in SI units, you should probably use a projected grid ...
- 8,466
6
votes
Calculate slope of line segments with QGIS
There is a new QGIS plugin called Road Slope Calculator that seems to do this. Quoting its project description:
This algorithm is used to calculate the longitudinal slope of forest
paths and roads, ...
- 10.8k
6
votes
Accepted
Changing DEM resolution when creating a slope raster?
Before creating your slope layer (Slope tool is the right choice) you can use the Resample tool to change the cellsize of your input raster, without changing the rasters extent.
It is however ...
- 944
6
votes
Accepted
Obtaining slope and aspect for points in QGIS
Run the following QGIS Processing Algorithms against your DEM:
Slope
Aspect
Once you have your newly generated Slope & Aspect rasters, run the Point Sampling tool against each to retrieve your ...
- 2,659
6
votes
Determining homogenity of flatroofs based on digital surface model / slope layer using QGIS
You could run "Raster pixels to polygons", to convert your raster to a vector layer:
Make sure your Buildings have a unique id, then run "Intersection" with your Buildings:
So ...
- 30.4k
6
votes
Accepted
Drawing slope signature in QGIS
Automatic solution
I created a model that automatically creates the lines as you want as a layer style. Run the model, make the inputs and you get the style you want. Details about how I did it: see ...
- 55.4k
5
votes
Directional slope calculation
The direction is best described as a vector v = (v1, v2) = (cos(t), sin(t)) where t is the direction angle. Precompute these two components.
Next, after computing the slope and aspect grids for the ...
- 68.7k
5
votes
Accepted
Fixed distance between two contours in QGIS
This may be possible in a manual sort of way using the 'Advanced Digitizing Tools'
Using this tool you can specify a distance. Then you just need to set up your snapping options to snap on ...
- 4,362
5
votes
Slope layer with false results in QGIS?
As mentioned in comments by user30184 and GerardoJimenez this is due to the horizontal coordinates x and y having a different unit of measurement from the elevation coordinate z.
For example, having ...
- 10.1k
Only top scored, non community-wiki answers of a minimum length are eligible