Project

Aerial photography was captured over the Canterbury Region covering the Selwyn and Waimakariri Districts, and Christchurch City including Banks Peninsula, totalling approximately 5,243 km2. The area of capture covers part of the Canterbury Region in the South Island.

Data Acquisition

Aerial photography was captured using Vexcel's digital UCE100 camera during the 2020/2021 season.

Captured on the following dates

24 October 2020

13 November 2020

Camera

Photography captured using Vexcel's digital UCE100 camera fitted with the 100 mm lens and flown at an altitude of approximately 18,927 ft (5,769 m) with the lowest ground GSD set at 0.3 m.

Sun Angle

Imagery captured with a sun angle between 37.8 and 65.2 degrees

Flight Planning

SN14007 Canterbury Rural: 45 runs, 1,895 frames

Stereo capture: Forward overlap 60%, min 54%. Side overlap 35%, min 15%.

Environmental Specification

Imagery captured with no cloud or cloud shadow within the area of interest. Coastal and harbour areas captured within two hours either side of low tide.

Ground Control

A combination of existing control and LINZ benchmarks were used for aerial triangulation for this project.

Map Projection

All spatial data for this project provided in terms of New Zealand Transverse Mercator 2000 map projection (NZTM2000). The datum is New Zealand Geodetic Datum 2000 (NZGD2000). The vertical datum is orthometric New Zealand Vertical Datum 2016 (NZVD2016).

Image Processing

Level-0 to Level-3 image processing carried out using UltraMap software. All imagery has gone through QA checks ensuring there is no cloud cover and cloud shadow other than over the ocean. During aerial acquisition the aircraft on-board GPS navigation data and ground base station data collected and post processed. Level-3 imagery process provides model based colour correctness/radiometry and even tonal balance across each project area.

Aerial Triangulation (AT)

Aerial triangulation carried out using Intergraph ISAT software. The AT brings together the GPS data and imagery using a two part process which stitches the imagery together using tie point matching for the relative orientation phase and observing ground control points for the absolute orientation phase. LINZ control, 8 th order horizontal and 4 th order vertical and other existing control from Aerial Surveys control data base were used to strengthen the block adjustment or as independent checks on position during final QA of the ortho imagery. A final report is generated to check RMSE values are within specification.

DTM for Ortho Production

The digital terrain model used for this project was a combination of existing 2014 and 2018 lidar and a dtm derived from photogrammetric MatchT which was generated from the stereo imagery using a largely automated pixel matching and autocorrelation process. The DTM was edited for ortho production only.

Gridded DEM Extracted from DTM Generated for Orthos

The DTM points were extracted as a gridded (10 m) DEM and supplied as tiled files aligned to LINZ 1:5,000 sheet layout. The DEM data is not suitable for contour generation. DTM Accuracy: ±0.6 m @ 95% confidence level (2 sigma) in clear open areas over client area

Ortho Rectification Process

Ortho imagery created using Intergraph OrthoPro software. Ortho rectification is the process of removing (from the image) the effects of camera tip/tilt and displacement caused by terrain relief. During this process each frame is 'draped' over the terrain model and the photograph then becomes 'scaled' and 'levelled' in terms of true ground coordinates. The generation of seamlines between frames follow natural physical features such as ridges, valleys, roads and rivers. The seamlines are used for the final ortho mosaic that stitches the imagery together using feather mosaicking techniques. The ortho imagery is then extracted aligned to LINZ 1:5,000 sheet tile layout.