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-Page for documenting NSW lidar processing +====== Mapping from NSW Lidar with QGIS ======
-====== Intro ======+
 NSW Spatial Services have undertaken a program to map all of NSW using lidar (light detecting and ranging) NSW Spatial Services have undertaken a program to map all of NSW using lidar (light detecting and ranging)
 For details, see information on their [[http://spatialservices.finance.nsw.gov.au/mapping_and_imagery/environmental_spatial_programs|elevation program]]. For details, see information on their [[http://spatialservices.finance.nsw.gov.au/mapping_and_imagery/environmental_spatial_programs|elevation program]].
  
-Elevation data can best be accessed through the [[http://elevation.fsdf.org.au/|Geoscience Australia ELVIS program]], and then processed with a GIS such as [[https://www.qgis.org/en/site/index.html|QGIS]] to create useful topographic maps.+Elevation data can best be accessed through the [[http://elevation.fsdf.org.au/|Geoscience Australia ELVIS program]].
  
-====== Resources ====== +It can then processed with a GIS such as [[https://www.qgis.org/en/site/index.html|QGIS]] to create useful topographic maps. Instructions below are specifically for use with QGIS, though the general outline may be useful for other GISs.
-  * [[https://www.tandfonline.com/doi/full/10.1080/23729333.2017.1300998|A design of contour generation for topographic maps with adaptive DEM smoothing]] +
-  * [[http://www.jennessent.com/downloads/tpi-poster-tnc_18x22.pdf|Poster on TPI]]+
  
-====== Topographic maps ======+====== Topics ======
  
-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: +The original topics here have now been moved to their own pages.
-  * 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.+Any feedback/suggestions of improvements are welcome.
  
-===== Merge DEMs =====+===== Managing DEMs =====
  
-The NSW DEM data is supplied in 2km squares. The squares need to be merged into a single DEM for further operations.+  * [[nsw_download_dems|Downloading DEMs]] - how to download DEMs from the ELVIS service 
 +  * [[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.
  
-While this can be done in theory using a virtual raster, I have had poor performance with this. Any operation seems to result in screen redrawing, so moving around and zooming in and out is quite slow and painful.+===== Topographic maps =====
  
-Instead, I generally use the the Raster- > Miscellaneous -> Merge... function+There are several primary data items for topographic maps that can be generated using the DEM data from the NSW Lidar. 
  
-===== Fill Sinks =====+  * [[qgis_depressionless_dem|Hydrologically correct DEM]] - prior to further operations, it is usually important to make sure that your DEM is free of depressions. Otherwise these will mess up streams and possibly contours.
  
-From the initial DEM, first step is to Fill Sinks. Otherwise you will get sinks in the middle of watercourses, which will impact contours and stream networks. Note that the this approach needs to be used with care in areas where there are actual depressions.+Once you have a depressionless DEM, the following items can be generated: 
 +  * [[qgis_contours|Contours]] 
 +  * [[qgis_hydrology|Hydrology (Stream Network)]] 
 +  * [[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
  
-There are various related tools in the Processing Toolbox that will do this, including: +===== Styles =====
-  * SAGA : Terrain Analysis - Hydrology : Fill Sinks +
-  * SAGA : Terrain Analysis - Hydrology : Fill Sinks (Wang and Liu) +
-  * SAGA : Terrain Analysis - Hydrology : Fill Sinks XXL (Wang and Liu) +
  
-The results from all will be similar, but the Wang and Liu versions should be faster. +  * [[qgis_styling|Styling]] - download basic style files
  
-There are other approaches that deepen channels rather than fill sinks in order to get a hydrologically sound drainage network. For example +===== Automation =====
-  * SAGA : Terrain Analysis - Hydrology : Sink Removal  +
-has an option for this.+
  
-===== Contours =====+  * [[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
  
-There are various contour extraction algorithms in QGIS, for example: +===== Mobile apps =====
-  * GDAL : Raster Extraction : Contour (same as Raster -> Extraction -> Contour...)+
  
-Below is an example of contours created without and with sink removal. The contours on the right have been derived from a DEM where the sinks (in yellow on the left) have been filled. +  * [[qgis_qfield|QField]] - QField is an excellent Android app for for viewing projects created with QGIS 
-{{:2019_02_08_12_17_09_untitled_project_qgis.png?300|}} +  * [[https://merginmaps.com/|Mergin Maps]] - (Previously Input App) is a mobile app compatible with QGIS
-{{:2019_02_08_12_17_57_untitled_project_qgis.png?300|}}+
  
-==== Contour Labelling ====+===== Dumping Ground / WIP =====
  
-See separate page on [[[qgis_contour_labelling|QGIS Contour Labelling]] +==== Resources ==== 
- +  * [[https://www.tandfonline.com/doi/full/10.1080/23729333.2017.1300998|A design of contour generation for topographic maps with adaptive DEM smoothing]] 
-===== Hydrology (Stream Network) ===== +  * [[http://www.jennessent.com/downloads/tpi-poster-tnc_18x22.pdf|Poster on TPI by Andrew D. Weiss]]
- +
-The starting point for hydrology is a hydrologically sound DEM, as above. Use a fill sinks or channel deepening algorithm. +
- +
-==== Catchment Areas ==== +
- +
-Next step is to create Catchment Areas. Again, there is a Catchment Area tool (in fact several), and six methods within the tool. For the purpose of delineating watercourses in steep terrain, the choice of method probably makes little difference. +
- +
-  * SAGA : Terrain Analysis - Hydrology : Catchment Area +
- +
-This gives an output that is best viewed in log scale. You can do this via  +
-  * Raster -> Raster Calculator... +
-    *  log10 ( "Filled DEM@1" )  +
- +
-Use the log scale version to determine the cutoff for what streams you want to see and which ones are too small. 10000 seems to give comparable results to the existing 1:25000 maps. +
- +
-Note that if you don't have the entirety of the catchment, you may get erroneous results. +
- +
-==== Channel Network ==== +
- +
-The following tool can be used to create channels (streams) - there are other options: +
-  * SAGA : Terrain Analysis - Channels : Channel Network +
- +
-Use +
-  * Elevation = Filled DEM +
-  * Initiation Grid = Catchment Area +
-  * Initiation Type = Greater Than +
-  * Initiation Threshold = 10000 (or whatever number you have determined) +
- +
-{{:2019-02-08_12_41_50-channel_network.png?600|}} +
- +
-The raster channel network can then be classified and converted to vector. +
- +
-===== 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. +
- +
-==== 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 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 > 0) + 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 ====+[[https://grass.osgeo.org/grass78/manuals/addons/r.geomorphon.html|GRASS - r.geomorphon function information page]]. This is a different approach that could be taken for landform classification. Yet to be tested.
  
-Convert back to 0/1 data using Raster Calculator+[[https://docs.qgis.org/3.4/en/docs/training_manual/grass/grass_setup.html|Training lession for QGIS 3.4 on GRASS Setup and basic use]]. Specific GRASS setup is required to use any GRASS functions in QGIS.
  
-Use Translate: set Output Data Type = Byte, set NoData = 0+[[https://grasswiki.osgeo.org/wiki/Introduction_to_GRASS_GIS_with_terrain_analysis_examples|GRASS GIS example of terrain analysis using r.geomorphon]]
  
-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?!)+[[http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.706.8909&rep=rep1&type=pdf|Geomorphons - a pattern recognition approach to classification and mapping of landforms]] paper.
  
-==== Vectorising ====+[[https://whiteboxgeospatial.wordpress.com/2014/12/25/a-new-form-of-multi-scale-topographic-position-visualization/|Multiscale topographic position - WhiteboxTools]] blog post.
  
-Run r.to.vect: set Feature Type = line+[[https://jblindsay.github.io/wbt_book/available_tools/geomorphometric_analysis.html#multiscaletopographicpositionimage|Multiscale topographic position image - WhiteboxTools function - user manual entry]] 
 +==== Method ==== 
 +The below snip of Breakfast Creek makes use of TPI calculated from a LIDAR derived DEM. Only positive values for TPI as displayed, which indicate cliff-like features. It is then combined with contours and aerial imagery to convey the terrain of the area.
  
-Run v.clean: Cleaning Tool = rmdangle, Threshold = 5,10+{{:breakfast_creek_snip.jpg?400|TPI from LIDAR DEM combined with contours and imagery to show clifflines and terrain}}
  
nsw_lidar.1549595744.txt.gz · Last modified: 2019/02/08 14:15 by bushwalking
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