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nsw_lidar [2019/02/10 13:59] bushwalkingnsw_lidar [2019/02/11 08:28] bushwalking
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 For more options in compression, look at: For more options in compression, look at:
   * GRASS : [[https://grasswiki.osgeo.org/wiki/V.generalize_tutorial|v.generalize]]   * GRASS : [[https://grasswiki.osgeo.org/wiki/V.generalize_tutorial|v.generalize]]
 +V.generalize can also be used to smooth contours - possibly best done prior to simplificiation
  
 ==== Cleaning ==== ==== Cleaning ====
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 {{:2019-02-08_12_41_50-channel_network.png?600|}} {{:2019-02-08_12_41_50-channel_network.png?600|}}
  
-The raster channel network can then be classified and converted to vector.+==== Classification ==== 
 + 
 +For 1:25000 maps, I've had reasonable results from using the following formula in the Raster Calculator to classify the streams into categories. Different scales may need different bounds, and this doesn't account for significantly larger rivers. 
 + 
 +''( log10 ( "Catchment Area@1" ) >= x) * ( log10 ( "Catchment Area@1" ) < y) * ("Channel Network@1" != 0)'' 
 + 
 +  * Intermittent: 4-6.15 (x-y) 
 +  * Minor: 6.15-7.4  
 +  * Major: 7.4+ 
 + 
 +==== Convert to Vector and Simplify ==== 
 + 
 +Convert to vector using r.to.vect 
 + 
 +{{:qgis_raw_stream.png?600|}} 
 + 
 +The raw stream data is very jagged. Smooth using  
 +  * v.generalize 
 +  * Algorithm = Hermite (there are other options which can be used)  
 +  * Maximal tolerance value = 20 (in m, obviously scale dependent) 
 + 
 +Simplify using using: 
 +  * Vector geometry : Simplify 
 +Tolerance:? 
  
 ===== Clifflines ===== ===== Clifflines =====
nsw_lidar.txt · Last modified: 2023/06/02 12:33 by allchin09

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