Hot answers tagged

14 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, ...
user avatar
  • 29k
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" ...
user avatar
  • 12k
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 ...
user avatar
  • 15.5k
12 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 (...
user avatar
  • 11.8k
11 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/...
user avatar
11 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 ...
user avatar
  • 1,989
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, ...
user avatar
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 ...
user avatar
  • 29k
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 ...
user avatar
  • 21.4k
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 ...
user avatar
  • 7,137
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 ...
user avatar
  • 36.2k
8 votes

Calculating slope in percentage with QGIS

Use the gdaldem tool http://www.gdal.org/gdaldem.html as gdaldem slope input.dem output_in_percents.tif -p -of GTiff From the manual page: "-p : if specified, the slope will be expressed as percent ...
user avatar
  • 51.5k
8 votes
Accepted

Subtracting out slope (in general) of DEM using ArcGIS for Desktop?

Subtract the trend surface from the DEM. Linear trend (1st order polynomial) 2nd order polynomial trend Per @radouxju's comment - the trend line can be shifted down to avoid negative values by ...
user avatar
  • 51.8k
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 ...
user avatar
  • 10.8k
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 ...
user avatar
  • 19.8k
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
user avatar
  • 2,197
7 votes

Identifying south facing mountain land, above an elevation, within a slope range, less than fixed distance from major roadways

The following is a rough outline of what you might do. I won't include a great deal of detail, you can research further using these terms and/or ask new more specific questions. Note: you will need ...
user avatar
  • 51.8k
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 ...
user avatar
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. ...
user avatar
  • 4,078
7 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 ...
user avatar
  • 36.2k
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 ...
user avatar
  • 36.2k
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/...
user avatar
  • 26.2k
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 ...
user avatar
  • 6,973
6 votes
Accepted

Calculating Slope of Street Segments using ArcGIS Desktop?

If you do not care about what happens between your two ends (not that this is dangerous for long roads in hilly regions), here are the steps : 1) feature vertices to points (ask for START and for END)...
user avatar
  • 48.6k
6 votes
Accepted

Calculating Topographic Wetness Index (choosing from different algorithms)

I think this post in the SAGA GIS forum might prove useful in answering your question about how slope is calculated: https://sourceforge.net/p/saga-gis/discussion/354013/thread/27ecdc6b/ Also, based ...
user avatar
  • 2,010
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 ...
user avatar
  • 20.5k
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 ...
user avatar
  • 8,207
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 ...
user avatar
  • 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 ...
user avatar
  • 2,599
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 ...
user avatar

Only top scored, non community-wiki answers of a minimum length are eligible