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nsw_lidar [2019/02/10 02:59]
bushwalking
nsw_lidar [2019/02/10 21:28]
bushwalking
Line 62: Line 62:
 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: 2019/02/22 21:37 by bushwalking