Data Acquisition:

Airborne Laser Scanner (ALS) data was acquired from a fixed wing aircraft 16 August 2016 to 9 August 2018, using Aerial Surveys Optech Orion H300 LiDAR system and a Optech Galaxy system.

Please refer to survey report for survey specifications.

Data Processing:

The LiDAR sensor positioning and orientation (POS) was determined using the collected GPS/IMU datasets and Applanix POSPac software.

Please refer to survey report for benchmark and base station information.

The POS data was combined with the LiDAR range files and used to generate LIDAR point clouds in NZTM and ellipsoidal heights. This process was undertaken using Optech LMS LiDAR processing software. The data was checked for completeness of coverage. The relative fit of data in the overlap between strips was also checked.

The height accuracy of the ground classified LiDAR points was checked using open land-cover survey check site data collected by Sounds Surveying Ltd. This was done by calculating height differences statistics between a TIN of the LiDAR ground points and the checkpoints. The standard deviation statistic is 0.057 m; a RMS of 0.057 m and the average difference is -0.003 m.

LiDAR is relative to the control check points.

The positional accuracy of the LiDAR data has been checked by overlaying Sounds Surveying Ltd surveyed data over the LiDAR data displayed coded by intensity. The data was found to fit well in position.

The point cloud data was then classified withTerraSolid LiDAR processing software into ground and above ground returns using automated routines tailored to the project landcover and terrain.

All product deliverables supplied in terms of NZTM map projection and NZVD2016 height datum.

Classification of the point cloud followed the classification scheme below:

1 - Unclassified

2 - Ground

3 - Low Vegetation

4 - Medium Vegetation

5 - High Vegetation

6 - Building

12 - Overlap

These classifications were not mentioned in survey report but were found to be accurate for publication:

7 - Noise

8 - Model Key-Point

9 - Water

10 - Bridge Deck (Misclassified)

Bridge Deck points were reclassified by LINZ from class 10 to class 17 to follow LAS v1.4 (where class 10 is Rail), before providing the classified point cloud data to Open Topography.

There were also a small number of synthetic point in these files. These were deemed to be by LINZ a result of Classification Level 3 and does not affect the integrity of these classified point cloud files:

CL3_BA30_2016_1000_0844

CL3_BA31_2016_1000_2733

Lakes and large rivers were hydroflattened in the Bare Earth Digital Elevation Model.

Disclaimers with this dataset:

- Hydroflattening does not meet base specification for rivers.

- More than one type of interpolation in the dataset due to re-supplied tiles. This has caused edge artifacts and inconsistent appearance between some tiles.

- There are sporadic linear vertical offsets that correspond to the edge of swaths, where the vertical difference is greater than the vertical accuracy.

- There are some linear vertical offsets that are parallel to the tile boundaries, but offset to the north-west.

- Major spikes and dips were manually removed, but other artifacts may still be in the dataset.

- Bridges found in the DEM from spot checking were manually removed, however, some bridges may still remain in the DEM.

The deliverables to LINZ were:

1m gridded bare earth digital elevation model (DEM)

1m gridded digital surface model (DSM)

Classified point cloud