English Environment Agency LIDAR
Various experiments so far
- https://houseprices.io/lab/lidar/map - England-wide overview map tiles created by 'hanoz' who posted to hacker news
- Chillly blog - Lidar - Chris was taking an early look back in June
- Chillly blog - More Lidar Goodness - featuring GDAL commands
- Chillly blog - Extracting building heights from LIDAR
- http://relief.raggedred.net - Chilly's map
- Phil Endecote posted experiments in edge detection
- User:EdLoach/Tendring LIDAR - Notes by EdLoach
- http://www.loach.me.uk/Lidar/ - Map covering his area with OSM overlay
- big mailing list discussion September (more since)
- User:Firefishy has a full complete bulk mirror.
- User:Gregrs/lidar2tiles – BASH script using GDAL to create tiles showing surface features e.g. buildings plus tiles covering Canterbury
- https://enfarchsoc.org/opendata/ shows LIDAR tiles on an openstreetmap background.
The Environment Agency LIDAR data was first released in 2015 as an open data set (Open government licensed). The data includes both digital terrain (DTM) and digital surface (DSM) models. This directly provides elevation of the terrain from which contour lines can be computed with a range of open source software (e.g., GDAL and QGIS). In addition the heights of features such as buildings, trees and hedges can be computed from the difference between the two models. Outlines or heights of such features might be derived from the LIDAR data in order to be input as vectors into OpenStreetMap.
DSM is the scan of the surface features from the aircraft including buildings, hedges, trees and even cars. The DTM data are processed version of DSM to remove the objects on the land, such as buildings etc, to reveal the underlying terrain.
Data are available at resolutions ranging from 2 metres down to 25 cm (2m, 1m, 50cm & 25cm). Around 85% of England is covered by 1m or 2m resolution data, but finer scale data is much patchier and focussed on areas most at risk of flooding.
Data is not necessarily very recent. In many areas it may be at least 5 years old. Comparison with local knowledge, Bing images and OSM data can be used to provide a rough estimate of age.
Most data tiles appear to be accurately aligned to OSGB grid boundaries. Tiles are natively in the OSGB projection (EPSG:27700). The LIDAR process means that this data does not suffer from parallax artefacts which often make aerial imagery difficult to interpret. However some 'clutter' is present, largely as obvious artefacts over water.
The following composite datasets are currently available as tile layers:
2m DTM 2020 (>93% coverage) https://data.gov.uk/dataset/a58f4e0d-27ba-440a-9a9c-274bc76500f5/lidar-composite-dtm-2020-2m https://environment.data.gov.uk/spatialdata/lidar-composite-digital-terrain-model-dtm-2m-2020/wms
2m DSM 2017 (~75% coverage) https://data.gov.uk/dataset/fba12e80-519f-4be2-806f-41be9e26ab96/lidar-composite-dsm-2017-2m
1m DTM 2020 (>88% coverage) https://data.gov.uk/dataset/b1ff0a9c-74d3-4b97-a3fb-c8ab39ef6152/lidar-composite-dtm-2020-1m https://environment.data.gov.uk/spatialdata/lidar-composite-digital-terrain-model-dtm-1m-2020/wms
1m DSM 2017 (>60% coverage) https://data.gov.uk/dataset/80c522cc-e0bf-4466-8409-57a04c456197/lidar-composite-dsm-2017-1m
Some tiles are available via Flickr without any georeferencing https://www.flickr.com/photos/environmentagencyopensurveydata/albums
Composite DSM & DTM data is available for download.
Deriving data for OpenStreetMap
Some of the above linked experiments are potential starting points for a process of deriving data which could be input into OpenStreetMap. In particular we may be able to vectorise building outlines or (more simply) get the height of buildings suitable for height=* values.
Some data input tests so far:
Importing or manual importing may be possible on a larger scale, but would only be carried out after deriving a separate data file, and probing the quality of this first.
The DTM data can be very helpful for mapping cliffs and paths, particularly in wooded areas, or identifying courses of ditches or streams for ground verification.