Waimate 0.075m Urban Aerial Photos (2021)

Camera

Imagery for this schedule was acquired using the Leica ADS100 line scanning camera with SH100 sensor head. The camera was fitted to a Leica PAV100 HP high performance gyro-stabilised mount.


Capture dates and sun angle
Imagery was acquired on 4-5th Novemeber, and 26th December 2021. The capture sun angle was > 45°.


Flight Planning

Careful consideration was given during flight planning to geographic location, terrain, topographical characteristics of the area, acquisition efficiency, final output resolution and meeting the various requested orthophoto quality specifications.

No. of flight lines: 27
Total length of flight lines (km): 188.5
Side overlap range (%): 40.2 - 55.5
Altitude range (m AMSL): 886.7 - 1082.6
Max altitude difference per AOI (m AMSL): 0 - 32.9
GSD range (cm): 4 - 7

Environmental Specification

All imagery was captured without the presence of cloud or cloud shadow within the specified areas of interest.
Where affected, all coastal, harbour, and tidal regions were captured during low tide periods, this being defined as the period 2 hours either side of low tide. Imagery covering coastal areas extends from the tide line during low tide periods out to 100 meters. Imagery of harbour areas extends out to 100 meters from the perimeter of the harbour.
Rivers were captured during times of appropriate flow/stage height/rainfall restrictions as specified by the client. These criteria were set to avoid periods of high river flow (flooding), rather than to target abnormally low river flows.



Elevated Feature Displacement

As detailed in the above published flight planning parameters, the area was flown with a minimum of 40 % side overlap as limited by the Nadir sensor. This was done to mitigate the effects of elevated feature displacement in an urban area.



Ground Control

A total of 42 ground control points were observed for use with the aerial triangulation and bundle
adjustment. Data from Global Survey’s and LINZ CORS sites, along with several existing LINZ benchmarks, were used in Leica Infinity software to process and check the ground control.



Map Projection and Datum

All spatial data for this project is supplied in the New Zealand Transverse Mercator (NZTM2000) projection in terms of the New Zealand Geodetic Datum 2000 (NZGD2000).



Image Processing

Landpro partnered with Hexagon Geosystems for image processing.


Aerial Triangulation (AT)

No abnormalities or complications were encountered during this phase. All aerial triangulations were carried out to ensure accuracies of less than 1 x GSD value. This was achieved with all adjusted RMS residual values at less than 7.5 cm, ensuring excellent overall quality and spatial accuracy.


Digital Terrain Model (DTM)

XPro uses Semi-Global Matching (SGM) for high-resolution DSM computation. A ratio of 1:1 was used for generation resulting in a 7.5cm GSD resolution point cloud. Semi-Global Matching filtration was done in Batch Converter and consisted of two processes following one after the other: Lasground to filter input data and extract ground points from input point cloud, and Lasclip for removal of ground points inside polygons with buildings. The resulting point cloud was used to produce a 32-bit floating raster DTM for use in orthophoto generation.
The following accuracy requirements have been met for this DTM:
Vertical Accuracy ≤1 metre (@ 90% confidence)
Horizontal Accuracy ≤1 meter (@ 90% confidence)
Grid spacing = 1 meter cell size

Orthorectified aerial photography
Individual radiometric profiles were used for each strip ensuring optimal results across the final ortho-mosaic. No complications were encountered during orthophoto generation, mosaicking and tiling. Various quality checks including accuracy, colour, contrast, sharpness, seamline positioning, refraction and generation artifacts were performed and found satisfactory on the final orthophoto tiles.

Peripheral imagery
Aerial imagery has been supplied for full tiles where the AOI covers part of a tile. The supplied imagery outside of the defined areas of interest has been orthorectified with the same DTM used to generate the primary AOI orthophotos.