Changes between Version 9 and Version 10 of FAQRaster

Timestamp:

Jun 6, 2008, 4:48:50 PM (16 years ago)

Author:

springmeyer

Comment:

Added further examples to gdal_rasterize and clipping with gdal_translate examples

FAQRaster

@@ -29 +29 @@
 Examples of other tools: [http://www.osgeo.org/qgis/ Quantum GIS], [http://www.osgeo.org/grass/ GRASS], [http://www.osgeo.org/mapserver/ MapServer], [http://gmt.soest.hawaii.edu/ GMT], [http://www.saga-gis.uni-goettingen.de/ SAGA GIS].
 
+However, if your raster format supports transparency in the Alpha band (RGBA), then you can use gdal_rasterize to burn in fully transparent areas into your image like :
+{{{
+$ gdal_rasterize -b 4 -burn 0 -where your_field=some_value -l your_layer your_vector_file.shp your_raster
+}}}
+
 == How do I use gdal_translate to extract or clip a sub-section of a raster? ==
 
 Gdal_translate is designed to convert to and from a variety of raster formats, but it can also perform helpful geoprocessing operations during conversion. 
 
-For example, if you would like to extract a sub-section of a raster you can use the -srcwin or -projwin options. In gdal terminology these are "subsetting" operations that allow you to select a "subwindow" to copy from the source dataset into the destination dataset. Currently, clipping raster images using vector extent polygons is not supported but is under discussion (see [http://trac.osgeo.org/gdal/ticket/1599])
+If you would like to extract a sub-section of a raster you can use the -srcwin or -projwin options. In gdal terminology these are "subsetting" operations that allow you to select a "subwindow" to copy from the source dataset into the destination dataset. 
 
-Here is an example of using gdal_translate on NAIP orthophotography in sid format to select a small subwindow that shows of Blakely Island, WA:
+Here is an example of using gdal_translate on NAIP orthophotography in sid format to select a small subwindow that shows Blakely Island, WA:
 {{{
-gdal_translate -of GTiff -co TFW=YES -co INTERLEAVE=BAND -projwin 510286 5385025 518708 5373405 ortho_1-1_1n_s_wa055_2006_1.sid naip_ortho_blakely_island.tif
+$ gdal_translate -projwin 510286 5385025 518708 5373405 ortho_1-1_1n_s_wa055_2006_1.sid naip_ortho_blakely_island.tif
 }}}
 
 This example uses the -projwin option which accepts the bounding coordinates in the projected coordinates rather than in pixels (-srcwin).  Gdal_translate -projwin needs the upper left x coordinate, the upper left y coordinate, the lower right x coordinate, and the lower right y coordinate. The naip imagery in this example is in NAD 83 Utm 10, so to get these bounding coordinates I simply loaded up the index shapefile that comes packaged with naip imagery in Quantum GIS and read the screen coordinates to form my extent. 
 
-If you don't care what section you want to clip out but just want to preview a portion of the raster use gdalinfo to get the bounding/corner coordinates and select an arbitrary subset that fits within those extents.
+Note: Currently, clipping raster images using vector extent polygons is not supported but is under discussion (see [http://trac.osgeo.org/gdal/ticket/1599]). However is is fairly easy to get the extents of a given shapefile and convert those coordinate pairs into the format needed by gdal_translate without manually reading the extents from another application like qgis. Say you have a shapefile named `clipping_mask.shp` use ogrinfo to get the extents:
+ * note the use of the pipe and grep command is optional(`| grep Extent`), but is a slick way to limit the info reported by ogrinfo to just what you need in this case
 
-Also, this example uses the optional -co switch to use name=value tages for a given format. For Geotiff many are available [http://www.gdal.org/frmt_gtiff.html] and in this example allowed the generation of a world file and band interleaving.
+{{{
+$ ogrinfo clipping_mask.shp -so -al | grep Extent
+# which gives the extent as xMin,yMin, xMax, yMax:
+Extent: (268596, 5362330) - (278396, 5376592)
+# which is (xMin,yMin) - (xMax,yMax)
+}}}
+Then copy and paste that text to create your gdal_translate clipping command:
+{{{
+# -projwin's ulx uly lrx lry is equivalent to xMin, yMax, xMax, yMin so just switch the Y coordinates
+# For the above Extent that would turn into:
+$ gdal_translate -projwin 268596 5376592 278396 5362330 src_dataset dst_dataset
+}}}
+
+.