QGIS Terrain Analysis (Slope, Aspect, Hillshade, contour lines)
Summary
TLDRThe video script explains how to use an algorithm to calculate the angle of inclination from a raster layer, expressed in degrees. It details importing a DEM layer, using the slope command for analysis, customizing the output appearance, and generating an aspect map indicating the slope's compass direction. The script also covers creating a hillshade effect for terrain visualization, adjusting sun azimuth, and extracting contour lines from a DEM layer to show elevation changes. It emphasizes the importance of selecting proper parameters and demonstrates how different settings affect the output.
Takeaways
- 📏 The algorithm calculates the angle of inclination of terrain from an input raster layer, expressing the slope in degrees.
- 🌍 To apply the slope, you need a DEM (Digital Elevation Model) layer imported into the software using the data source management tool.
- 🖼️ Go to the raster section, select your layer from the requested path, and click add to enter the software.
- 🛠️ In the raster section, select the slope command from the analysis section and enter your layer to see the final output.
- 🎨 Customize the appearance by going to the layer properties section, selecting render type from the symbology section, setting it on platted, and choosing a color combination.
- 📐 The aspect command generates an aspect map from any supported elevation raster, showing the compass direction a slope faces.
- 🧭 To perform the aspect command, go to the raster section, select the aspect command from the analysis section, select the desired layer, and set an output path.
- 🌄 Hill shade outputs a raster with a shaded relief effect, useful for visualizing terrain, allowing adjustments for azimuth and altitude of the light source.
- 🔄 To apply the hill shade command, select the hill shade option from the raster and analysis section, enter the desired layer, and optionally change some parameters.
- 🗺️ Contour lines indicate ground elevation or depression on a topographic map, with intervals set to specify the distance between lines, providing insights into elevation changes.
Q & A
What does the algorithm calculate from the input raster layer?
-The algorithm calculates the angle of inclination of the terrain from the input raster layer, with the slope expressed in degrees.
What is required to apply the slope command?
-A Digital Elevation Model (DEM) is required to apply the slope command.
How do you import a DEM layer into the software?
-To import a DEM layer, use the Data Source Management tool, go to the raster section, select the layer from the requested path, and click add.
How do you customize the appearance of the slope output?
-To customize the appearance, go to the layer properties section, select render type from the symbology section, set it on platted, and choose a color combination.
What does the aspect command generate?
-The aspect command generates an aspect map from any supported elevation raster, indicating the compass direction that a slope faces.
How is the aspect measured and what does it represent?
-The aspect is measured in degrees from 0 to 360 degrees from North, indicating the azimuth, or compass direction, that a slope faces.
What is the purpose of the hill shade command?
-The hill shade command outputs a raster with a shaded relief effect, useful for visualizing terrain, and allows specifying azimuth, altitude of the light source, vertical exaggeration factor, and scaling factor.
What input is necessary for the hill shade command?
-The input for the hill shade command must be a DEM layer.
What is a contour line and its interval?
-A contour line is drawn on a topographic map to indicate ground elevation or depression, and a contour interval is the vertical distance or difference in elevation between contour lines.
How do you extract contour lines and set the interval?
-To extract contour lines, go to the raster section, select the Contour option from the extraction section, input the DEM layer, and specify the distance between contour lines, such as setting it to 10 meters.
Outlines
📐 Slope Calculation and Customization
This paragraph explains the process of calculating the slope of terrain from an input raster layer, which is expressed in degrees. The slope is calculated using a Digital Elevation Model (DEM), which is imported into the software. The user navigates through the software's data source management tool to add the DEM layer to the raster section. The slope command is then selected from the analysis section, and the input layer is specified. The final output is the slope command output, which can be customized in terms of appearance by selecting a render type and color combination. The aspect command generates an aspect map, which shows the compass direction a slope faces, and can be adjusted for visualizing terrain. The hill shade command is also mentioned, which outputs a raster with a shaded relief effect, allowing users to specify the light source's azimuth, altitude, and scaling factor for better visual representation.
🌡️ Contour Lines Extraction and Interpretation
The second paragraph delves into the process of extracting contour lines from a DEM layer, which are used to indicate ground elevation or depression. Contour intervals, the vertical distance between contour lines, are crucial for understanding terrain changes. The user selects the Contour option from the extraction section, specifying the DEM layer as the input. The distance between contour lines can be set, with the example of creating contour lines every 10 meters or 80 meters. The color of the contour lines can be adjusted to highlight areas with extreme elevation changes or areas with lower density. This process provides a visual representation of the terrain's elevation, aiding in the interpretation of the landscape.
Mindmap
Keywords
💡DEM
💡Slope
💡Aspect
💡Hill Shade
💡Contour Line
💡Azimuth
💡Symbology
💡Raster
💡Analysis Section
💡Contour Interval
Highlights
Algorithm calculates terrain inclination angle from raster layer input.
Slope expressed in degrees and requires a DEM for application.
Import DEM layer using data source management tool.
Navigate to raster section to select and add the layer.
Use slope command in analysis section for terrain analysis.
Customize appearance by adjusting layer properties and render type.
Aspect command generates a map of slope compass directions.
Aspect values range from 0 to 360 degrees, indicating azimuth from North.
Hill shade effect visualizes terrain with shaded relief.
Adjustable parameters for light source, vertical exaggeration, and scaling in hill shade.
Contour lines indicate ground elevation on topographic maps.
Contour interval defines the vertical distance between lines.
Extract contour lines using the Contour option from the extraction section.
Specify distance between contour lines for elevation analysis.
High density of contour lines indicates more extreme elevation changes.
Lower density contour lines suggest less change in altitude.
Adjust contour line distance for clearer elevation changes.
Transcripts
foreign
this algorithm calculates the angle of
inclination of the terrain from an input
raster layer the slope is expressed in
degrees
to apply the slope you'll need a Dem so
we import a Dem layer into the software
for this purpose use the data source
management tool go to the raster section
select your layer from the requested
path
and click add to enter the software
go to the raster section
select the slope command from the
analysis section
enter your layer
that's it here is the final output
now we're going to customize its
appearance so we go to the layer
properties section
and select render type from the
symbology section
we set it on platted
and choose a color combination
here you can see the slope command
output
aspect command generates an aspect map
from any supported elevation raster
aspect is the compass direction that a
slope faces the pixels will have a value
from 0 to 360 Degrees measured in
degrees from North indicating the
azimuth
to perform this command go to the raster
section
select the aspect command from the
analysis section
select the desired layer
you can set an output path
done here you can see the aspect output
Hill shade outputs a raster with a nice
shaded relief effect it's very useful
for visualizing the terrain you can
optionally specify the Azimuth and
altitude of the light source a vertical
exaggeration factor and a scaling factor
to account for differences between
vertical and horizontal units to apply
this command like slope and aspect
select the hill shade option from the
raster and Analysis section
enter the desired layer as input
note that the input must be a Dem
you can define a storage path to the
output
you can change some parameters
in the first step we do it by default
here is the hill shade output
brighter areas are areas where the sun
shines directly on these areas
select the hill shade again
change the Azimuth of the sun this time
by changing the Azimuth the angle of the
sun will be different
a contour line is a line drawn on a
topographic map to indicate ground
elevation or depression a contour
interval is the vertical distance or
difference in elevation between contour
lines here to extract contour lines you
need to go to the raster section select
the Contour option from the extraction
section
the input should be the Dem layer
you can also specify the distance
between two contour lines here we set it
on 10 meters to start so that a contour
line is created for us every 10 meters
because we have a large area and there
are many 10 meter lines in this area it
will take some time
foreign
a better color can be chosen
areas with a high density of contour
lines have more extreme elevation
changes
on the contrary the areas with lower
density do not have many changes in
altitude
once again we set the distance between
the two lines on 80 meters
here the changes in the contour lines
are clear
foreign
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