nsw_lidar
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nsw_lidar [2021/02/19 19:41] – bushwalking | nsw_lidar [2021/03/04 22:05] – 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 ===== | ||
- | * [[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 | + | * [[qgis_basic_automation|Basic map creation]] - a set of PyQGIS scripts that will create (and optionally save) a basic topographic |
- | * 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/ | + | ===== Mobile apps ===== |
- | ===== Clifflines ===== | + | * [[qgis_qfield|QField]] - QField is an excellent Android app for for viewing projects created with QGIS |
+ | * [[https:// | ||
- | 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' | ||
- | |||
- | 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