nsw_lidar
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nsw_lidar [2018/10/04 21:46] – processing data bushwalking | nsw_lidar [2024/04/05 19:00] (current) – Add download bushwalking | ||
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- | Page for documenting NSW lidar processing | + | ====== |
- | ====== | + | |
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:// | ||
- | Elevation data can best be accessed through the [[http:// | + | Elevation data can best be accessed through the [[http:// |
- | ====== Resources ====== | + | It can then processed with a GIS such as [[https:// |
- | * [[https:// | + | |
- | * [[http:// | + | |
- | ====== | + | ====== |
- | There are several primary data items for topographic maps that can be generated using the DEM data from the NSW Lidar. | + | 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/ | + | Any feedback/ |
- | ===== Contours | + | ===== Managing DEMs ===== |
- | ===== Hydrology (Stream Network) ===== | + | * [[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. | ||
- | ===== Clifflines | + | ===== Topographic maps ===== |
- | The steps below have been tested in the Blue Mountains, a region | + | There are several primary data items for topographic maps that can be generated using the DEM data from the NSW Lidar. |
- | ==== Initial analysis of slope, aspect ==== | + | * [[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. |
- | SAGA -> Terrain Analysis | + | Once you have a depressionless DEM, the following items can be generated: |
+ | * [[qgis_contours|Contours]] | ||
+ | * [[qgis_hydrology|Hydrology (Stream Network)]] | ||
+ | * [[qgis_slope|Slopes]] | ||
+ | * [[qgis_clifflines|Clifflines]] | ||
- | Extract | + | ===== Styles ===== |
- | 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 ==== | + | * [[qgis_styling|Styling]] - download basic style files |
- | Next convert data to 1 bit (1,2 not 0,1, as Sieve ignores 0s) using Raster Calculator. | + | ===== Automation ===== |
- | Formula is: (Slope > 0) + 1 | + | |
- | Then Sieve resulting data using a Threshold | + | * [[qgis_basic_automation|Basic map creation]] - a set of PyQGIS scripts |
- | + | ||
- | Also good to rerun Sieve with smaller Threshold | + | |
- | a) get rid of some small dangles. | + | |
- | b) fill small holes. | + | |
- | + | ||
- | Additional smoothing | + | |
- | 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' | + | ===== Mobile apps ===== |
- | Matrix | + | * [[qgis_qfield|QField]] - QField |
- | 0.0 0.5 0.0 | + | * [[https:// |
- | 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 | + | ===== Dumping Ground |
- | If the original matrix is 1/2 then the cutoff will be 3.5 | + | ==== Resources ==== |
- | + | * [[https://www.tandfonline.com/ | |
- | This step could be run multiple times - some testing would need to be done to determine how many times. | + | * [[http:// |
- | + | ||
- | Other options | + | |
- | ==== 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