Slope Analysis using Quantum GIS Processing Toolbox - Revision history

Abrownlee at 03:59, 5 October 2024

2024-10-05T03:59:14Z

Abrownlee: /* References */

2024-10-04T23:51:06Z

References

Abrownlee: /* Raster Calculations */

2024-10-04T23:47:34Z

Raster Calculations

Abrownlee: /* Exporting your model */

2024-10-04T21:41:48Z

Exporting your model

Abrownlee: /* Displaying output rasters from model */

2024-10-04T21:33:26Z

Displaying output rasters from model

Abrownlee: /* Running a model */

2024-10-04T15:21:43Z

Running a model

Abrownlee: /* Hillshade */

2024-10-04T14:48:17Z

Hillshade

Abrownlee: /* Aspect */

2024-10-04T14:37:52Z

Aspect

Abrownlee: /* Slope */

2024-10-04T05:15:19Z

Slope

Abrownlee: /* Inverse Distance Weighted (IDW) */

2024-10-04T05:00:23Z

Inverse Distance Weighted (IDW)

@@ Line 57: / Line 57: @@
 [[File:Proj.Selection.png|frameless|center]]
- Once enabled, filter search '''NAD83 (1)''' and select '''NAD83''' under the '''Geographic Coordinate Systems''' '''(2)'''. When finished select '''OK (3)'''.
+ Once enabled, filter search '''NAD83''' and select '''NAD83''' under the '''Geographic Coordinate Systems''' '''(2)'''. When finished select '''OK (3)'''.
@@ Line 72: / Line 72: @@
 [[File:Selecting.CSV.png|frameless|center]]
-Next you will be asked to choose the projection that the data has. Under '''Geometry Definition''', ensure that you define the proper coordinate system in which the points will be displayed. As before, filter search '''NAD83 (1)''' and select '''NAD83''' under the '''Geometry CRS (2)'''. When finished, select '''OK (3)'''.
+Next you will be asked to choose the projection that the data has. Under '''Geometry Definition''', ensure that you define the proper coordinate system in which the points will be displayed. As before, filter search '''NAD83''' and select '''NAD83''' under the '''Geometry CRS (2)'''. When finished, select '''OK (3)'''.
 [[File:Geometry.Definition.png|frameless|center]]
@@ Line 168: / Line 168: @@
 Following the IDW interpolation, a slope map expressed in degrees will be created using the IDW output.
-Execute a search filter for '''Slope (1)''', and select '''Slope (2)''' under '''GDAL/OGR'''.
+Execute a search filter for '''Slope''', and select '''Slope''' under '''GDAL/OGR'''.
 [[File:Slope.algorythm.png|frameless|center]]
-This will display a window for the Slope geoalgorithm '''(3)'''. Leave the field parameters as default except for '''Slope expressed as percent''' to '''No'''. Make sure that the '''Input layer''' is the '''Interpolated IDW output'''.
+This will display a window for the Slope geoalgorithm. Leave the field parameters as default except for '''Slope expressed as percent''' to '''No'''. Make sure that the '''Input layer''' is the '''Interpolated IDW output'''.
 Also add an '''Output raster''' name of your choice. Select '''OK'''.
@@ Line 180: / Line 180: @@
 ====Aspect====
-Execute a search filter for '''Aspect (1)''', and select '''Aspect (2)''' under '''GDAL/OGR'''.
+Execute a search filter for '''Aspect''', and select '''Aspect''' under '''GDAL/OGR'''.
 [[File:Aspect.algorithm.png|frameless|center]]
-This will display a window for the Aspect geoalgorithm '''(3)'''. Leave the specifications as default. Make sure that the '''Input layer''' is the '''Interpolated IDW output'''.
+This will display a window for the Aspect geoalgorithm. Leave the specifications as default. Make sure that the '''Input layer''' is the '''Interpolated IDW output'''.
 Also add an '''Output raster''' name of your choice. Select '''OK'''.
@@ Line 192: / Line 192: @@
 ====Hillshade====
-Execute a search filter for '''Hillshade (1)''', and select '''Hillshade (2)''' under '''GDAL/OGR'''.
+Execute a search filter for '''Hillshade''', and select '''Hillshade''' under '''GDAL/OGR'''.
 [[File:Hillshade.algorithm.png|frameless|center]]
-This will display a window for the Hillshade geoalgorithm '''(3)'''. Leave the specifications as default. Make sure that the '''Input layer''' is the '''Interpolated IDW output'''.
+This will display a window for the Hillshade geoalgorithm. Leave the specifications as default. Make sure that the '''Input layer''' is the '''Interpolated IDW output'''.
 Also add an '''Output raster''' name of your choice. Select '''OK'''.
@@ Line 230: / Line 230: @@
 [[File:IDW.properties2.png|frameless|center]]
-A '''Layer Properties''' window will appear. Navigate to '''Symbology (1)''', select the '''Render type''' to '''Singleband pseudocolour (2)'''. The rest of the properties can be changed to your personal desire. For my output I selected '''Spectral (3)''' for the color and '''Quantile''' mode '''(4)''' and then selected '''OK (4)'''.
+A '''Layer Properties''' window will appear. Navigate to '''Symbology''', select the '''Render type''' to '''Singleband pseudocolour'''. The rest of the properties can be changed to your personal desire. For my output I selected '''Spectral''' for the color and '''Quantile mode''' and then selected '''OK'''.
 [[File:IDW.symbology.2.png|frameless|center]]

← Older revision		Revision as of 23:51, 4 October 2024
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	R.E. Crochiere and L.R. Rabiner. (1983). Multirate Digital Signal Processing. Englewood Cliffs, NJ: Prentice–Hall.		R.E. Crochiere and L.R. Rabiner. (1983). Multirate Digital Signal Processing. Englewood Cliffs, NJ: Prentice–Hall.

			ESRI, (n.d.). ''How inverse distance weighted interpolation works.'' ArcGIS Pro Help. https://pro.arcgis.com/en/pro-app/latest/help/analysis/geostatistical-analyst/how-inverse-distance-weighted-interpolation-works.htm

@@ Line 265: / Line 265: @@
 ==Raster Calculations==
-In addition to creating a model using the Processing toolbox, the '''QGIS raster calculator''' can be used to input certain expressions to preform multiple geoprocessing tasks. For the purposes of this tutorial I will be extracting all areas from the slope map that are not flat, (i.e. '''don't have a slope of 0 degrees''').
+In addition to creating a model using the Processing toolbox, the "QGIS raster calculator" can be used to input certain expressions to perform multiple geoprocessing tasks.
+For the purposes of this tutorial, we will start by extracting all areas from the slope map that are not flat (i.e., "don't have a slope of 0 degrees").
 First navigate to the menu bar, under '''Raster''', select '''Raster Calculator...'''.
-[[File:CalcSelection.png]]
+[[File:Raster.calculator2.png|frameless|center]]
+A '''Raster calculator''' window will open. Inside the raster calculator expression field, insert the expression in the image below. Remember, '''''your expression should reflect the names you have given your output layers'''''. If you have named your raster band differently than I have, please insert the name of your raster band in the place of mine. I would recommend manually clicking the operators to avoid typing errors. When done entering the expression, at the bottom of the window it should say "expression valid".
+[[File:Raster.calc.expression2.png|frameless|center]]
+Remember to save the output as something that is easily recognizable, and Select '''OK'''. I named mine "SlopeCalc".
+When finished, you should have an output map like the one indicated below. All areas without a slope of 0 degrees are represented in black and all other areas are in white.
+[[File:Slopecalc2.png|frameless|center]]
+Next, we are going to extract all areas from the aspect map with a south-facing slope. To account for southeast and southwest-facing slopes, I created an expression that included all slopes with aspect values ranging from 135 to 225 as "south-facing." Inside the raster calculator expression field, insert the expression in the image below. Again, your expression should reflect the names you have given your output layers. If you have named your raster band differently than I have, please insert the name of your raster band in the place of mine. Again, I recommend manually clicking the operators to avoid typing errors. Remember to save the output as something that is easily recognizable, and Select '''OK'''. I named mine "AspectCalc".
+[[File:AspectCalc.png|frameless|center]]
+When finished, we are left with a layer where areas without aspect values between 135 and 225 are represented in black, and all other areas are in white.
+[[File:Aspect.calc.layer.png|frameless|center]]
-A '''Raster calculator''' window will open. Inside the expression field insert the following expression '''(1)''': '''( "Output Slope@1" > 0 ) OR ( "Output Slope@1" < 0 )'''. I would recommend manually clicking the operators to avoid typing error. When done entering the expression, at the bottom of the window it should say "expression valid".
+Finally, we are going to create a layer which combines the two we just created. This layer will highlight areas that are not flat and are south-facing. In the raster calculator, input the expression in the image below. This combines the attributes of both layers we created in previous steps.
-Remember to save the output as something that is easily recognizable '''(2)''', example, SlopeCalc.tif. Select '''OK (3)'''.
-[[File:RasterCalculator.png]]
+[[File:Slope.and.aspect.png|frameless|center]]
-When finished you should have an output map like the one indicated below. All areas without a slope of 0 degrees are represented in black and all other areas are in white.
+We are then left with a layer that highlights all sloped and south-facing areas of the raster grid in white, with all other areas in black.
-[[File:SlopeCalc.png|box]]
+[[File:Slopeandaspect.result.png|frameless|center]]
-The following process can be done for any of the output terrain maps. Extracting areas without a slope of 0 degrees was done as an example.
+The following process can be done for any of the output terrain maps.
 ==Conclusion==

@@ Line 246: / Line 246: @@
 Once you finish your model it can be exported for further use.
-[[File:ModelOutput.png]]
 ====As an Image====
-If you'd like to print out the finished model or include it in a report it is possible to save the model as an image for future reference a picture of the model can be saved using the indicated button '''(1)'''.
+If you'd like to print out the finished model or include it in a report it is possible to save the model as an image for future reference a picture of the model can be saved using the indicated button.
+[[File:Export.as.image.png|frameless|center]]
 ====As a Python script====
-It is also possible to export the model as Python script using the second indicated button '''(2)'''.
+It is also possible to export the model as Python script using the second indicated button.
-This Python script can be edited in a program such as Notepad++.
+[[File:Export.as.python.png|frameless|center]]
+This button will display the model as a python script. From there it can be saved to an appropriate location with the '''Save as''' button. This Python script can be edited in a program such as Notepad++.
-[[File:PythonModel.png]]
+[[File:Model.as.python.png|frameless|center]]
 ==Raster Calculations==

@@ Line 228: / Line 228: @@
 One way to change this is to change this '''right click''' on '''Output IDW''', select '''Properties'''.
-[[File:IDWProperties.png]]
+[[File:IDW.properties2.png|frameless|center]]
-A '''Layer Properties''' window will appear. Navigate to '''Style (1)''', select the '''Render type''' to '''Singleband pseudocolour (2)'''. The rest of the properties can be changed to your personal desire. For my output I selected '''Spectral (3)''' for the color and '''Quantile''' mode '''(4)''' and then selected '''OK (4)'''.
+A '''Layer Properties''' window will appear. Navigate to '''Symbology (1)''', select the '''Render type''' to '''Singleband pseudocolour (2)'''. The rest of the properties can be changed to your personal desire. For my output I selected '''Spectral (3)''' for the color and '''Quantile''' mode '''(4)''' and then selected '''OK (4)'''.
-[[File:IDWSymbology.png]]
+[[File:IDW.symbology.2.png|frameless|center]]
 This process can be done for any of the output raster layers. The IDW output was done as an example. The output should look similar to the capture below, depending on the cell size used in the modeling process.
-[[File:IWDOutput.png]]
+[[File:IDWoutput2.png|frameless|center]]
 It is also possible to change the transparencies of the layers and overlay them on top of one another for more visually pleasing final maps. The following map was created by setting the transparency of the IDW layer to 10% and overlaying it onto of the Hillshade layer.
-[[File:IWDAndHillShadeOutput.png]]
+[[File:Idwplushillshade.png|frameless|center]]
 ===Exporting your model===

@@ Line 206: / Line 206: @@
 Once all of the geoprocessing algorithms have been added, the model should look similar to the capture below.
+[[File:Model.should.looklikedis.png|frameless|center]]
-Make sure that you '''Save (1)''' the model before '''Running the model (2)'''.
+Make sure that you save the model to an appropriate place before running it.
-[[File:RunModel.png]]
+[[File:Save.model.as.png|frameless|center]]
-When the '''Run model''' button is select, a window the same as the capture below will appear.
+Click the '''Run model''' button at the top of the model designer, which appears to the user as a little play button.
-In this window make sure you save the output files to an appropriate destination folder. Select '''OK''' to run the model.
-Also check to make sure that '''PointDataShapefile''' is the '''Input elevation points''' that will be Transformed first in the model.
+When the '''Run model''' button is selected, a window the same as the capture below will appear. In this window, make sure you save the output files to an appropriate destination folder. Select '''Run''' to run the model. In this window, check to make sure that your elevation point shapefile is the '''Input elevation points''' that will be transformed first in the model.
+[[File:Model.parameters.and.outputs.png|frameless|center]]
-[[File:FullModel.PNG]]
 Once the model is finished running, the output layers will be displayed in the '''Layer''' toolbox on the left side.
-[[File:LayerOutput.png]]
+[[File:Model.output.layers.png|frameless|center]]
 ===Displaying output rasters from model===

@@ Line 193: / Line 193: @@
 Execute a search filter for '''Hillshade (1)''', and select '''Hillshade (2)''' under '''GDAL/OGR'''.
+[[File:Hillshade.algorithm.png|frameless|center]]
 This will display a window for the Hillshade geoalgorithm '''(3)'''. Leave the specifications as default. Make sure that the '''Input layer''' is the '''Interpolated IDW output'''.
@@ Line 198: / Line 200: @@
 Also add an '''Output raster''' name of your choice. Select '''OK'''.
-[[File:HillShade.png]]
+[[File:Hillshade.parameters.png|frameless|center]]
 ===Running a model===

@@ Line 148: / Line 148: @@
 ====Inverse Distance Weighted (IDW)====
-The second algorithm that will be added is an '''Inverse Distance Weighted (IDW)''' [http://en.wikipedia.org/wiki/Interpolation interpolation]. This particular algorithm can be found by doing a search filter for '''IDW (1)''', and select '''v.surf.idw (2)''' under '''GRASS Commands'''.
+The second algorithm that will be added is an '''Inverse Distance Weighted (IDW)''' [https://pro.arcgis.com/en/pro-app/latest/help/analysis/geostatistical-analyst/how-inverse-distance-weighted-interpolation-works.htm]. This interpolation technique works by assuming that points closer to one another are more similar than those further apart. To predict a value for any unmeasured location, the IDW algorithm uses this assumption as well as the measured values surrounding it (ESRI, n.d.). This particular algorithm can be found by doing a search filter for '''IDW''', and select '''v.surf.idw''' under '''GRASS Commands'''.
+[[File:V.surf.idw.png|frameless|center]]
-A window will open asking for interpolation specifications '''(3)'''. Enter the specifications that you desire.
+A window will open asking for interpolation specifications. Enter the specifications that you desire.
 Make sure that the '''Input layer''' is the output from the '''2D to 3D transformation'''.
-For my slope analysis, I had to enter '''Z''' into the '''Attribute table column with values to interpolate''' field because the column under the '''PointDataShapefile''' Attribute Table used for elevation points is named '''Z'''.
+For my slope analysis, I had to enter '''Z''' into the '''Attribute table column with values to interpolate''' field because the column under the '''PointDataShapefile''' Attribute Table used for elevation points is named '''Z'''. Also add an '''Output raster''' name of your choice.
+[[File:V.surf.idw.parameters.png|frameless|center]]
-I also used a '''GRASS region cellsize''' of '''0.0005'''. This can be changed if you'd like, although it may take longer to process with a smaller cell size value. Also add an '''Output raster''' name of your choice. Select '''OK'''.
+I also used a '''GRASS region cellsize''' of '''0.0005''' which can be modified under '''Show advanced parameters'''. This can be changed if you'd like, although it may take longer to process with a smaller cell size value.  Select '''OK'''.
-[[File:IDW.png]]
+[[File:V.surf.idw.advanced.png|frameless|center]]
 ====Slope====