nsw_lidar
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nsw_lidar [2021/02/20 09:52] – bushwalking | nsw_lidar [2021/02/20 10:01] – bushwalking | ||
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====== Topics ====== | ====== Topics ====== | ||
- | The original topics here are being progressively | + | The original topics here have now been moved to their own pages. |
+ | |||
+ | Any feedback/ | ||
===== Managing DEMs ===== | ===== Managing DEMs ===== | ||
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* [[qgis_hydrology|Hydrology (Stream Network)]] | * [[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_slope|Slopes]] - while not a standard feature of topographic maps, this can be a simple way to identify cliffs | ||
- | * Clifflines | + | * [[qgis_clifflines|Clifflines]] - a work in progress |
===== Styles ===== | ===== Styles ===== | ||
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* [[qgis_qfield|QField]] - QField is an excellent Android app for for viewing projects created with QGIS | * [[qgis_qfield|QField]] - QField is an excellent Android app for for viewing projects created with QGIS | ||
- | ====== Topographic maps ====== | + | ===== Dumping Ground / WIP ===== |
- | 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: | ||
- | * 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/ | ||
- | |||
- | ===== Clifflines ===== | ||
- | |||
- | 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. | ||
- | |||
- | 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' | ||
- | |||
- | 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' | ||
- | |||
- | 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 ==== | ||
- | |||
- | 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/ | ||
- | |||
- | ==== Vectorising ==== | ||
- | |||
- | Run r.to.vect: set Feature Type = line | ||
- | |||
- | Run v.clean: Cleaning Tool = rmdangle, Threshold = 5,10 | ||
- | |||
- | ===== Dumping Ground / WIP ===== | ||
==== Resources ==== | ==== Resources ==== | ||
* [[https:// | * [[https:// |
nsw_lidar.txt · Last modified: 2024/04/05 19:00 by bushwalking