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nsw_lidar [2021/02/19 19:41]
bushwalking
nsw_lidar [2021/03/04 22:05] (current)
bushwalking
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 ====== Topics ====== ====== Topics ======
  
-The original topics here are being progressively moved to their own pages+The original topics here have now been moved to their own pages
 + 
 +Any feedback/suggestions of improvements are welcome.
  
 ===== Managing DEMs ===== ===== Managing DEMs =====
  
-  * [[nsw_dems|Merging DEMs]] - how to merge DEMs in QGIS+  * [[nsw_merge_dems|Merging DEMs]] - how to merge DEMs in QGIS
   * [[nsw_dems|Managing large DEMs]] - while data can be downloaded in an ad hoc manner, if you are regularly processing NSW DEMs, it is better to have the DEM tiles already downloaded. This page provides steps to do this in an automated manner.   * [[nsw_dems|Managing large DEMs]] - while data can be downloaded in an ad hoc manner, if you are regularly processing NSW DEMs, it is better to have the DEM tiles already downloaded. This page provides steps to do this in an automated manner.
  
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   * [[qgis_contours|Contours]]   * [[qgis_contours|Contours]]
   * [[qgis_hydrology|Hydrology (Stream Network)]]   * [[qgis_hydrology|Hydrology (Stream Network)]]
-  * Clifflines+  * [[qgis_slope|Slopes]] - while not a standard feature of topographic maps, this can be a simple way to identify cliffs 
 +  * [[qgis_clifflines|Clifflines]] - a work in progress
  
-===== Mobile apps =====+===== Styles =====
  
-  * [[qgis_qfield|QField]] - QField is an excellent Android app for for viewing projects created with QGIS+  * [[qgis_styling|Styling]] - download basic style files
  
-====== Topographic maps ======+===== Automation =====
  
-There are several primary data items for topographic maps that can be generated using the DEM data from the NSW Lidar. The main ones are: +  * [[qgis_basic_automation|Basic map creation]] - a set of PyQGIS scripts that will create (and optionally save) a basic topographic map. This map can be used in QField
-  * Contours +
-  * Hydrology (Stream Network) +
-  * Clifflines+
  
-The steps below are works in progress to determine effective (the best?) ways to extract the various items out of the DEM data for use in topographic maps. Any feedback/suggestions of improvements are welcome.+===== Mobile apps =====
  
-===== Clifflines =====+  * [[qgis_qfield|QField]] - QField is an excellent Android app for for viewing projects created with QGIS 
 +  * [[https://inputapp.io/en/|input App]] - input App is an iOS app compatible with QGIS
  
-The steps below are being developed for use in the Blue Mountains, a region that has a significant number of relatively vertical sandstone cliffs. It may be less effective in different terrain.+===== Dumping Ground / WIP =====
  
-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 ==== 
- 
-SAGA -> Terrain Analysis - Morphometry -> Slope, Aspect, Curvature 
- 
-Extract  
- Slope, Aspect  
-using DEM and [1] Maximum Triangle Slope (Tarboton (1997)). I haven't tested any other algorithms.  
-  
-Cliff areas can be identified using a range of say 60-90 and 70-90 degrees on the Slope file. Using 60-90 degrees helps connect logical cliffs and avoid small breaks. 
- 
-==== Initial Cleaning ==== 
- 
-Next convert data to 1 bit (1,2 not 0,1, as Sieve ignores 0s) using Raster Calculator. 
-Formula is: (Slope > 60) + 1 
- 
-Then Sieve resulting data using a Threshold of 100 and 8-connectedness to get rid of small non-connected cliffs. Note above that Sieve doesn't like 0s. 
-  
-Also good to rerun Sieve with smaller Threshold (1-10) and 4-connectedness to  
-a) get rid of some small dangles. 
-b) fill small holes. 
-  
-Additional smoothing can be done using a User Defined Filter with the following matrix. This will apply some smoothing by allowing you to reclassify the pixel values, and remove single pixel indentations like this: 
- 000    000 
- 101 -> 111 
- 111    111 
-and single pixel protrusions like this: 
- 000    000 
- 010 -> 000 
- 111    111 
- 
-The main problem is that the matrix has to be defined each time in QGIS. There doesn't seem to be an option to load it. Possibly this can be done outside QGIS. 
- 
-Matrix is: 
- 0.0 0.5 0.0 
- 0.5 0.5 0.5 
- 0.0 0.5 0.0 
- 
-If the original matrix is 0/1 then the cutoff will be 1.5 
- 
-If the original matrix is 1/2 then the cutoff will be 3.5 
- 
-This step could be run multiple times - some testing would need to be done to determine how many times. 
-  
-Other options for cleaning the data include a plugin called LecoS, but this doesn't work on QGIS 3. Another possibility is Shrink and Expand - radius 1? But this also creates some new holes that didn't previously exist, so not ideal. 
- 
-==== Thinning ==== 
- 
-Convert back to 0/1 data using Raster Calculator 
- 
-Use Translate: set Output Data Type = Byte, set NoData = 0 
- 
-Run r.thin - r.thin is quite picky about the input file format. Needs to be NULL/non-NULL (not float or int). The Translate process above provides this. The previous two steps could be combined into one. Also, this file may need to be explicitly saved (not just a temporary file?!) 
- 
-==== Vectorising ==== 
- 
-Run r.to.vect: set Feature Type = line 
- 
-Run v.clean: Cleaning Tool = rmdangle, Threshold = 5,10 
- 
-===== Dumping Ground / WIP ===== 
 ==== Resources ==== ==== Resources ====
   * [[https://www.tandfonline.com/doi/full/10.1080/23729333.2017.1300998|A design of contour generation for topographic maps with adaptive DEM smoothing]]   * [[https://www.tandfonline.com/doi/full/10.1080/23729333.2017.1300998|A design of contour generation for topographic maps with adaptive DEM smoothing]]
nsw_lidar.1613724094.txt.gz · Last modified: 2021/02/19 19:41 by bushwalking