Spatial subset

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(→‎Vector polygon masking)
(→‎Vector polygon masking)
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* Right click on Layer name in the Layers Panel . {{mitem|text=Export --> Save Features as...}} {{button|text=Save as...}}. Fill the form as shown below.
 
* Right click on Layer name in the Layers Panel . {{mitem|text=Export --> Save Features as...}} {{button|text=Save as...}}. Fill the form as shown below.
 
* Click the checkbox '''Save only the selected features'''.
 
* Click the checkbox '''Save only the selected features'''.
 +
* The target coordinate reference system (CRS) is WGS84 / UTM zone 32 (EPSG:32632).
 
[[File:Qgis_vector_save_as.png|300px]]
 
[[File:Qgis_vector_save_as.png|300px]]
  
 
Make sure that the CRS is the same like the image file (here WGS84/UTM Zone 32, EPSG:32632)!
 
Make sure that the CRS is the same like the image file (here WGS84/UTM Zone 32, EPSG:32632)!
−
# Click {{button|text=OK}}.
+
* Click {{button|text=OK}}.
−
# {{mitem|text=Raster --> Extraction ---> Clip Raster by Mask Layer...}}
+
* {{mitem|text=Raster --> Extraction ---> Clip Raster by Mask Layer...}}
−
# Input file (raster): Choose a loaded file name fron the drop down list or click {{button|text=Select}} to browse to a file (see above).
+
# Input file (raster): Choose a loaded file name from the drop down list or click {{button|text=Select}} to browse to a file
−
# Output file:  click {{button|text=Select}} to choose a new file name for the subset image.
+
# Mask layer: Select the exported vector file (s. above).
−
# Change the clipping mode from '''Extent''' to '''Mask'''. Choose the newly created polygon of the municipality as '''Mask Layer'''.
+
# Clipped (mask)):  click {{button|text=Select}} to choose a new file name for the subset image.
 
# Switch the checkbox on: '''Crop the extent of the target dataset to the extent of the cutline'''. All image data outside the polygon will be masked.
 
# Switch the checkbox on: '''Crop the extent of the target dataset to the extent of the cutline'''. All image data outside the polygon will be masked.
−
# Switch the '''No data value''' checkbox on and specify the value {{typed|text=0}}.
+
# Switch '''Keep resolution of output raster''' on.
−
# Click {{button|text=OK}}.
+
# Choose output data type {{typed|text=Uint16}.
 +
# Click {{button|text=Run in Background}}.
 
[[File:Qgis_raster_mask.png|600px]]
 
[[File:Qgis_raster_mask.png|600px]]
 
[[Category: Working with Raster Data]]
 
[[Category: Working with Raster Data]]

Revision as of 12:47, 29 October 2018

Interactive box selection

  1. Click the Open Data Source Manager QGIS 3.0 datasource.png and Add raster layer QGIS 2.0 addrast.png and select the file /geodata/raster/s2/Subset_S2A_MSIL2A_20170619T_MUL.tif.
  2. Raster --> Extraction ---> Clip Raster by Extent
  3. Input file (raster): Choose a loaded file from the drop down list or click Select to browse for a file.
  4. Output file: click Select to choose a new file name for the subset image.
  5. Define the clipping extent by clicking... and Select extent from canvas The clipping mode is now active. Hold a left click on the map canvas dragging a box of your region of interest.
  6. Adjust the extent coordinates in the text file rounding the coordinates (upper left and lower right).

Qgis raster clipper.png

  1. Click OK.

Vector polygon masking

  • Load the vector file \geodata\vector\gadm36_DEU_4.shp. These are the level 4 administrative boundaries of the country Germany downloaded from https://gadm.org/index.html .
  • Right click on Layer name in the Layers Panel Properties --> General. Change the Data source encoding from System to UTF-8. Click UTF-8.
  • Right click on Layer name in the Layers Panel and open the Attribute table.
  • Click Qgis select by expression.png and select by the expression: "NAME_4" ='Göttingen'. Select.

Qgis select munic.png

  • Right click on Layer name in the Layers Panel . Export --> Save Features as... Save as.... Fill the form as shown below.
  • Click the checkbox Save only the selected features.
  • The target coordinate reference system (CRS) is WGS84 / UTM zone 32 (EPSG:32632).

Qgis vector save as.png

Make sure that the CRS is the same like the image file (here WGS84/UTM Zone 32, EPSG:32632)!

  • Click OK.
  • Raster --> Extraction ---> Clip Raster by Mask Layer...
  1. Input file (raster): Choose a loaded file name from the drop down list or click Select to browse to a file
  2. Mask layer: Select the exported vector file (s. above).
  3. Clipped (mask)): click Select to choose a new file name for the subset image.
  4. Switch the checkbox on: Crop the extent of the target dataset to the extent of the cutline. All image data outside the polygon will be masked.
  5. Switch Keep resolution of output raster on.
  6. Choose output data type {{typed|text=Uint16}.
  7. Click Run in Background.

Qgis raster mask.png

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