Spatial subset

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(→‎Vector Polygon)
(→‎Masking by vector polygon)
 
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== Interactive box selection ==
 
== Interactive box selection ==
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# Click the {{button|text=Add raster layer}} [[Image:QGIS_2.0_addrast.png|20px]] and select the file  ''C:/OSGeo4W64/geodata/raster/s2/Subset_S2A_MSIL2A_20170619T.tif''.
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# Click the {{button|text=Open Data Source Manager}} [[Image:QGIS_3.0_datasource.png|30px]] and {{button|text=Add raster layer}} [[Image:QGIS_2.0_addrast.png|20px]] and select a multiband raster file.
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# After clicking {{button|text=Open}}, the raster layer appears on the QGIS canvas.
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# {{mitem|text=Raster --> Extraction ---> Clip Raster by Extent}}
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# {{mitem|text=Raster --> Extraction ---> Clipper...}}
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# Input layer: Choose a loaded raster file from the drop down list or click [[File:QGIS_file_select.png]] to browse for a file.
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# Input file (raster): Choose a loaded file name fron the drop down list or click {{button|text=Select}} to browse to a file.
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# Define the clipping extent by clicking [[File:QGIS_file_select.png]] and select '''Draw on canvas'''. The clipping mode is now active. Hold a left click on the map canvas dragging a box of your region of interest.
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# Output file:  click {{button|text=Select}} to choose a new file name for the subset image.
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# Clipped (extent): click [[File:QGIS_file_select.png]] to choose a new file name for the subset image.
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# The clipping mode '''extent''' is now active. Hold a left click on the map canvas dragging a box of your region of interest.
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# Adjust the extent coordinates in the text file rounding the coordinates (upper left and lower right).
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# Adjust the extent coordinates in the text file rounding the coordinates of 1 (upper left corner) x, y and 2 (lower right corner) x, y.
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[[File:Qgis_raster_clipper.png|700px]]
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[[File:Qgis_raster_clipper.png|600px]]
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* Click {{button|text=Run}}.
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# Click {{button|text=OK}}.
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== Vector Polygon ==
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== Masking by vector polygon ==
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# Load the vector file ''C:\OSGeo4W64\var\geodata\vector\Landkreis_Goe_neu_utm32.shp''. This is the actual boundary of the county Göttingen. We create a new vecto file with the boundary of the municipality Göttingen.
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* Load the vector file (e.g. administrative boundary).
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# Right click on Layer name in the Layers Panel{{mitem|text=Properties --> General}}. Change the '''Data source encoding''' from {{button|text=System}} to {{button|text=UTF-8}}. Click {{button|text=UTF-8}}.
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* Select a community of your choice: right click {{mitem|text=Open Attribute Table}}
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# Right click on Layer name in the Layers Panel and open the {{button|text=Attribute table}}.
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# Click [[File:Qgis_select_by_expression.png]] and select by the expression: {{typed|text="NAME_4" ='Göttingen'}}. {{button|text=Select}}.
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* {{mitem|text=Raster --> Extraction ---> Clip Raster by Mask Layer...}}
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[[File:Qgis_select_munic.png|400px]]
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# Input layer: Choose a loaded raster file from the drop down list or click [[File:QGIS_file_select.png]] to browse to a file.
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# Right click on Layer name in the Layers Panel {{button|text=Save as...}}. Fill the form as shown below.
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# Mask layer: Select the vector file (s. above).
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[[File:Qgis_vector_save_as.png|400px]]
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# Assign a specofied nodata value: {{button|text=65535}}
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Make sure that the CRS is the same like the image file!
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# Switch the checkbox on: '''Match the extent of the clipped raster to the extent of the mask layer'''. All image data outside the polygon will be masked.
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# Clipped (extent)):  click {{button|text=Select}} to choose a new file name for the subset image.
 
# Click {{button|text=Run}}.
 
# Click {{button|text=Run}}.
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# {{mitem|text=Raster --> Extraction ---> Clipper...}}
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[[File:Qgis_raster_mask.png|400px]]
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# 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).
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# Output file:  click {{button|text=Select}} to choose a new file name for the subset image.
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# Change the clipping mode from '''Extent''' to '''Mask'''. Choose the newly created polygon of the municipality as '''Mask Layer'''.
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# 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.
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# Switch the '''No data value''' checkbox on and specify the value {{typed|text=0}}.
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# Click {{button|text=OK}}.
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[[File:Qgis_raster_mask.png|600px]]
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[[Category: Working with Raster Data]]
 
[[Category: Working with Raster Data]]

Latest revision as of 10:57, 31 May 2021

[edit] 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 a multiband raster file.
  2. Raster --> Extraction ---> Clip Raster by Extent
  3. Input layer: Choose a loaded raster file from the drop down list or click QGIS file select.png to browse for a file.
  4. Define the clipping extent by clicking QGIS file select.png and select Draw on canvas. The clipping mode is now active. Hold a left click on the map canvas dragging a box of your region of interest.
  5. Clipped (extent): click QGIS file select.png to choose a new file name for the subset image.
  6. Adjust the extent coordinates in the text file rounding the coordinates (upper left and lower right).

Qgis raster clipper.png

  • Click Run.

[edit] Masking by vector polygon

  • Load the vector file (e.g. administrative boundary).
  • Select a community of your choice: right click Open Attribute Table
  • Raster --> Extraction ---> Clip Raster by Mask Layer...
  1. Input layer: Choose a loaded raster file from the drop down list or click QGIS file select.png to browse to a file.
  2. Mask layer: Select the vector file (s. above).
  3. Assign a specofied nodata value: 65535
  4. Switch the checkbox on: Match the extent of the clipped raster to the extent of the mask layer. All image data outside the polygon will be masked.
  5. Clipped (extent)): click Select to choose a new file name for the subset image.
  6. Click Run.

Qgis raster mask.png

Retrieved from "http://wiki.awf.forst.uni-goettingen.de/wiki/index.php?title=Spatial_subset&oldid=16356"
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