Creating a multi-band GeoTIFF

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{{construction}}
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: ''In this exercise you will learn how to create composites of several bands of satellite data.  
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: ''This exercise is part of the [[QGIS Tutorial 2013/14]].<br/>In this exercise you will learn how to create images of several bands of satellite data, and how to georeference a raster image.''
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==Multiband layers==
 
==Multiband layers==
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To create a multiband image:
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Satellite image data are most often delivered as single band image files. For displaying colour composites and classification single band image files need to be stacked and saved into a multi-band image:
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# Load the different satellite band layers into [[QGIS]]. For exercise purposes, you can use the landsat-bands from the directory ''geodata/raster/landsat/'' in the [[Course data|course data]]; the layer names start with ''sub'', the band number is indicated by ''B'' and a one- or two-digit number, e.g. ''B1'' or ''B10'' for the first band and ''B1'' or ''B20'' for the second.
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# Load the different satellite band layers into [[QGIS]]. For exercise purposes, you can use Sentinel-2 satellite bands from the directory ''geodata\Goe\raster\sentinel-2\''; the band number is indicated by ''B'' and two-digit number, e.g. ''B01'' for the first band and ''B02'' for the second. Important for producing a correct output multi-band file is that the band layer are ranked in ascending order in the ''Layer browser''. Usually single bands with the same spatial resolution (GSD or pixel size) are stacked in a file. In case of Sentinel-2 band designation please find information on spectral and spatial resolution.  
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# If the processing toolbox is not visible in you [[QGIS]] window yet, select {{mitem|text=Processing --> Toolbox}}.  
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# If the processing toolbox is not visible, select {{mitem|text=Processing --> Toolbox}}.  
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# In the processing toolbar, type {{typed|text=merge}} into the search field to find the {{button|text=merge}} tool and open it.
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# In the processing toolbar, type {{typed|text=Merge}} into the search field to find the {{button|text=GDAL\OGR --> Merge}} tool and open it ('''figure A''').
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# Click the upper {{button|text=...}} button to select the layers you want to combine. There are different reasonable ways to combine spectral bands, depending on the information you want to obtain:
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# Click the button {{button|text=...}} on to select the layers you want to include in the multi-layer band.
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#* True color (RGB=3,2,1) simulates the natural color.
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# Activate {{button|text=Layer stack}}
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#* Standard false color (RGB=4,3,2) makes healthy vegetation generally appear red.
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# Choose the same ''Output raster type'' as the data storage type of the single input bands.
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#* False color (RGB=5,4,3 or 4,5,3) tends to distinguish different landcover material.
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# The output file should be named with the extension '''.tif''' to indicate GeoTIFF file format.  
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# In the {{button|text=Layer stack}} pulldown-menu, select {{button|text=Yes}}.
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[[Image:RemSens_Exercise03_1.png|thumb|left|800px|'''Figure A:''' The ''Merge'' dialogue in [[QGIS]] 2.14]]
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# Click the bottom {{button|text=...}} button to select directory and file name to save the result. You can skip this step if you only want to save the result temporarily.
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# Check the box {{button|text=Open output file after running algorithm}} (if not checked per default) and click {{button|text=Run}}. The resulting map should be added to the [[TOC]] automatically after the algorithm has finished, under the name ''Output layer''.
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[[Category:Working with Raster Data]]
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# If necessary, you can rearrange the bands by opening the layer [[Exercise 01: First steps in QGIS|properties]] and selecting the {{button|text=Style}} tab. Adjust the bands as you see fit and confirm with {{button|text=Apply}} or {{button|text=OK}}.
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## For some color composites, (e.g. true color composites), the image may be enhanced by selecting {{button|text=Stretch to MinMax}} from the {{button|text=Contrast enhancement}} menu and selecting the {{button|text=Mean +/- standard deviation x}} radio button. After adjusting the standard deviation factor (a value between 1 and 2 should do), click {{button|text=Load}} and confirm with {{button|text=Apply}} or {{button|text=OK}}.
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Latest revision as of 09:24, 2 May 2016

In this exercise you will learn how to create composites of several bands of satellite data.

[edit] Multiband layers

Satellite image data are most often delivered as single band image files. For displaying colour composites and classification single band image files need to be stacked and saved into a multi-band image:

  1. Load the different satellite band layers into QGIS. For exercise purposes, you can use Sentinel-2 satellite bands from the directory geodata\Goe\raster\sentinel-2\; the band number is indicated by B and two-digit number, e.g. B01 for the first band and B02 for the second. Important for producing a correct output multi-band file is that the band layer are ranked in ascending order in the Layer browser. Usually single bands with the same spatial resolution (GSD or pixel size) are stacked in a file. In case of Sentinel-2 band designation please find information on spectral and spatial resolution.
  2. If the processing toolbox is not visible, select Processing --> Toolbox.
  3. In the processing toolbar, type Merge into the search field to find the GDAL\OGR --> Merge tool and open it (figure A).
  4. Click the button ... on to select the layers you want to include in the multi-layer band.
  5. Activate Layer stack
  6. Choose the same Output raster type as the data storage type of the single input bands.
  7. The output file should be named with the extension .tif to indicate GeoTIFF file format.
Figure A: The Merge dialogue in QGIS 2.14
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