nsw_lidar
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nsw_lidar [2019/02/09 22:41] – bushwalking | nsw_lidar [2023/06/02 12:33] – [Mobile apps] allchin09 | ||
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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:// | For details, see information on their [[http:// | ||
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It can then processed with a GIS such as [[https:// | It can then processed with a GIS such as [[https:// | ||
- | ====== | + | ====== |
- | * [[https:// | + | |
- | * [[http:// | + | |
- | ====== Topographic maps ====== | + | The original topics here have now been moved to their own pages. |
- | 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: | + | Any feedback/ |
- | * 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/ | + | ===== Managing DEMs ===== |
- | ===== Merge DEMs ===== | + | * [[nsw_merge_dems|Merging |
+ | * [[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. | ||
- | The NSW DEM data is supplied in 2km squares. The squares need to be merged into a single DEM for further operations. | + | ===== Topographic maps ===== |
- | While this can be done in theory | + | There are several primary data items for topographic maps that can be generated |
- | Instead, I generally use the the Raster- > Miscellaneous -> Merge... function | + | * [[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. |
- | ===== Fill Sinks ===== | + | 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 | ||
- | From the initial DEM, first step is to Fill Sinks. Otherwise you will get sinks in the middle of watercourses, | + | ===== Styles ===== |
- | There are various related tools in the Processing Toolbox that will do this, including: | + | |
- | | + | |
- | * 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. | + | ===== Automation ===== |
- | There are other approaches | + | * [[qgis_basic_automation|Basic map creation]] - a set of PyQGIS scripts |
- | * SAGA : Terrain Analysis - Hydrology : Sink Removal | + | |
- | has an option for this. | + | |
- | ===== Contours | + | ===== Mobile apps ===== |
- | There are various contour extraction algorithms in QGIS, for example: | + | * [[qgis_qfield|QField]] - QField is an excellent Android app for for viewing projects created with QGIS |
- | * GDAL : Raster Extraction : Contour | + | * [[https:// |
- | 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. | + | ===== Dumping Ground / WIP ===== |
- | {{: | + | |
- | {{: | + | |
- | ==== Contour Labelling | + | ==== Resources |
- | + | | |
- | See separate page on [[[qgis_contour_labelling|QGIS Contour Labelling]] | + | * [[http://www.jennessent.com/downloads/tpi-poster-tnc_18x22.pdf|Poster |
- | + | ||
- | ===== Hydrology (Stream Network) ===== | + | |
- | + | ||
- | 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 | + | |
- | + | ||
- | * 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 ( " | + | |
- | + | ||
- | Use the log scale version to determine the cutoff | + | |
- | + | ||
- | 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 | + | |
- | * Initiation Grid = Catchment Area | + | |
- | * Initiation Type = Greater Than | + | |
- | * Initiation Threshold = 10000 (or whatever number you have determined) | + | |
- | + | ||
- | {{: | + | |
- | + | ||
- | 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' | + | |
- | + | ||
- | 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' | + | |
- | + | ||
- | 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' | + | |
- | + | ||
- | 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' | + | |
- | ==== Thinning ==== | + | [[https:// |
- | Convert back to 0/1 data using Raster Calculator | + | [[https:// |
- | Use Translate: set Output Data Type = Byte, set NoData = 0 | + | [[https:// |
- | 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:// |
- | ==== Vectorising ==== | + | [[https:// |
- | Run r.to.vect: set Feature Type = line | + | [[https:// |
+ | ==== 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? |
nsw_lidar.txt · Last modified: 2024/04/05 19:00 by bushwalking