This layer contains the DEM for LiDAR data in the Canterbury Region for Christchurch, captured between 18 December 2020 and 17 February 2021.
- The DSM is available as layer [Canterbury - Christchurch LiDAR 1m DSM (2020-2021)](https://data.linz.govt.nz/layer/109642).
- The index tiles are available as layer [Canterbury - Christchurch LiDAR Index Tiles (2020-2021)](https://data.linz.govt.nz/layer/109644).
- The LAS point cloud and vendor project reports are available from [OpenTopography](https://portal.opentopography.org/datasets?search=new%20zealand).
LiDAR was captured for Christchurch City Council by Landpro Ltd between 18 December 2020 and 17 February 2021. These datasets were generated by Landpro and their subcontractors. Data management and distribution is by Toitū Te Whenua Land Information New Zealand.
- DEM: tif or asc tiles in NZTM2000 projection, tiled into a 1:1,000 tile layout
- DSM: tif or asc tiles in NZTM2000 projection, tiled into a 1:1,000 tile layout
- Point cloud: las tiles in NZTM2000 projection, tiled into a 1:1,000 tile layout
Pulse density specification is at a minimum of 8 pulses/square metre.
Vertical Accuracy Specification is +/- 0.2m (95%) Horizontal Accuracy Specification is +/- 1.0m (95%)
Vertical datum is NZVD2016.
Airborne Laser Scanner (ALS) data was acquired from a fixed wing aircraft on 18/19/28 December 2020, 13/22/23/24/25/26 January 2021 and 17 February 2021, using Landpro's Leica ALS60 Laser scanner.
Port Hills and Lyttleton Harbour Flying Height: 1940 m AGL Scan Angle: ±11 degrees Pulse Rate: 123 kHz Swath Overlap: 55% Swath Points Per M2: 8
Data processing has been in accordance with our standard policies and procedures surrounding acceptable tolerances, therefore ensuring optimal accuracies of deliverables. GNSS/IMU data is processed utilising GSCC Base Station and precise ephemeris data. The GNSS and IMU are processed in Novatel Inertial Explorer to give an optimum trajectory.
This data is then applied to the LiDAR for LAS 1.4 creation in Leica Cloudpro. The geoidal adjustments are applied in Cloudpro, the data is now in NZTM with NZVD 2016 Heights.
Overlapping LiDAR points from adjacent aircraft trajectories were used to check the LiDAR calibration for heading, roll, pitch and scale. These values were then used to make small flight-specific adjustments to the LiDAR data.
Height accuracy of the ground classified LiDAR points was checked using check site data (non- vegetated check sites) collected by Landpro Ltd. This was done by performing an Output Control Report (OCR) in TerraSolid’s TerraScan, which calculates height differences statistics between a TIN of the LiDAR ground points and the check points. The standard deviation statistic is 0.03, RMS is 0.03, CI95 is 0.05m and the average difference is 0.000.
The positional accuracy of the LiDAR was checked by overlaying Landpro Ltd surveyed data over the LiDAR data displayed by intensity. The data fits into position.
The TerraSolid suite was used for the automated method of macro based bare-earth filtering. Multiple iterations of automated filtering were utilized to address the ever-changing terrain while retaining a homogenous surface. After automated filtering, manual editing was completed using TerraScan and TerraModeler in MicroStation. Editing was performed to ensure that 100% of the identified bare-earth surface was visually inspected for errors, completeness, and accuracy. Bridge decks were also classified. Points floating above or positioned below the bare earth surface were designated as low noise and high noise.
The Digital Elevation Model (DEM) was created using point to TIN and TIN to raster process, using Natural Neighbour interpolation. Hydro flattening was performed as stipulated in the LINZ Specification Version 1.1 – June 2018.
Classification of the point cloud follows the classification scheme below: 1 - Unclassified 2 - Ground 3 - Low Vegetation 4 - Medium Vegetation 5 - High Vegetation 6 - Buildings 7 - Low Noise 9 - Water 17 - Bridge Deck 18 - High Noise
Ground control was completed using existing benchmarks and survey data collected by Landpro Ltd, this was used in the vertical accuracy of the processed ground dataset. GPS base station data was provided by Global Survey’s CORS operating in Christchurch. Ground check points were surveyed by Landpro Ltd for assessing the accuracy of the ALS data.
Height accuracy of the classified LiDAR was checked using open land-cover survey check sites. This was done by comparing the test points against the elevations from the classified LiDAR dataset, yielding the following results:
Mean Difference (m) - 0.00 m Std Deviation (m) - 0.03 m RMS (m) - 0.03 m CI95 - 0.058
The deliverables to LINZ were:
1m gridded bare earth digital elevation model (DEM) 1m gridded digital surface model (DSM) Classified point cloud
All product deliverables supplied in terms of NZTM map projection and NZVD2016 vertical datum.