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nsw_lidar [2019/02/10 11:29] 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 =====
  
 The steps below have been tested in the Blue Mountains, a region that has a significant number of relatively vertical sandstone cliffs. It may be less effective in different terrain. The steps below have been tested in the Blue Mountains, a region that has a significant number of relatively vertical sandstone cliffs. It may be less effective in different terrain.
 +
 +This is more a set of ideas than a fully fledged process. The main aims are to get a set of steps that can largely be automated, and that create cliffline vectors that are running in the correct direction. There is still some way to go on this!
  
 ==== Initial analysis of slope, aspect ==== ==== Initial analysis of slope, aspect ====
nsw_lidar.txt · Last modified: 2023/06/02 12:33 by allchin09

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