Spatial subset

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(→‎Interactive box selection)
(→‎Masking by vector polygon)
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== Masking by vector polygon ==
 
== Masking by vector polygon ==
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* Load the vector file ''\geodata\lucc\gadm36_DEU_4.shp''. These are the level 4 administrative boundaries of the country Germany downloaded from https://gadm.org/index.html .
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* Load the vector file of the communities of county Göttingen e.g. ''\geodata_w01\VG250_GEM_KRS_Goettingen.gpkg''.
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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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−
[[File:Qgis_select_munic.png|400px]]
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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.
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* Click the checkbox '''Save only the selected features'''.
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−
* The target coordinate reference system (CRS) is WGS84 / UTM zone 32 (EPSG:32632).
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−
[[File:Qgis_vector_save_as.png|300px]]
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−
Make sure that the CRS is the same like the image file (here WGS84/UTM Zone 32, EPSG:32632)!
 
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* Click {{button|text=OK}}.
 
 
* {{mitem|text=Raster --> Extraction ---> Clip Raster by Mask Layer...}}
 
* {{mitem|text=Raster --> Extraction ---> Clip Raster by Mask Layer...}}
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# Input file (raster): Choose a loaded file name from the drop down list or click {{button|text=Select}} to browse to a file
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# Input file (raster): Choose a loaded file name from the drop down list or click {{button|text=Select}} to browse to a file. * Make sure that the CRS is the same like the image file (here WGS84/UTM Zone 32, EPSG:32632) that you wish to be clipped!
−
# Mask layer: Select the exported vector file (s. above).
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# Mask layer: Select the vector file (s. above).
 +
# Switch checkbox on: '''Selected features only'''.
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# Assign a specofied nodata value: {{button|text=65535}}
 
# Clipped (mask)):  click {{button|text=Select}} to choose a new file name for the subset image.
 
# 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.
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# Switch '''Keep resolution of output raster''' on.
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# Click {{button|text=Run}}.
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# Choose output data type: {{typed|text=Uint16}}.
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−
# Click {{button|text=Run in Background}}.
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[[File:Qgis_raster_mask.png|700px]]
 
[[File:Qgis_raster_mask.png|700px]]
 
[[Category: Working with Raster Data]]
 
[[Category: Working with Raster Data]]

Revision as of 11:38, 13 May 2020

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_w01/mosaic_S2B_MSIL2A_20190724T103029_N0213_R108_T32UNC_UNB_UPC.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.

Masking by vector polygon

  • Load the vector file of the communities of county Göttingen e.g. \geodata_w01\VG250_GEM_KRS_Goettingen.gpkg.
  • Select a community of your choice: right click Open Attribute Table
  • 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. * Make sure that the CRS is the same like the image file (here WGS84/UTM Zone 32, EPSG:32632) that you wish to be clipped!
  2. Mask layer: Select the vector file (s. above).
  3. Switch checkbox on: Selected features only.
  4. Assign a specofied nodata value: 65535
  5. Clipped (mask)): click Select to choose a new file name for the subset image.
  6. 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.
  7. Click Run.

Qgis raster mask.png

Retrieved from "http://wiki.awf.forst.uni-goettingen.de/wiki/index.php?title=Spatial_subset&oldid=15786"
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