Data Acquisition:

The aerial photography for this project was captured within the 2016/17 flying season (September

2016 – April 2017) on the following dates:

8th, 16th, 17th, 23rd, 27th February, 8th, 9th March 2017.

All photography was captured using Vexcel's digital UCE camera and flown at:

0.3 m GSD: 18928 ft (5769 m) flying height

Camera Lens: 100 mm

Sun Angle

Minimum of +35 degrees

Data Processing

All aspects of the data processing from imagery processing to DTM creation and ortho production

and product deliverables was undertaken in-house by Aerial Surveys staff & Cyient.

Map Projection

All spatial data for this project provided in terms of New Zealand Transverse Mercator (NZTM) map

projection. The datum is New Zealand Geodetic Datum 2000. The height datum is orthometric

Lyttelton 1937 (sea level).

Image Processing and Aerial Triangulation

All imagery has gone through QA checks ensuring there is no cloud cover and cloud shadow. During

aerial acquisition the aircraft on-board GPS navigation data and ground base station data collected

and post processed. Imagery processed to level 3 and checked for colour correctness/radiometry and

even tonal balance across each project area. The aerial triangulation 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, 8th order horizontal and 4th 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 Creation

The DTM creation was collected from stereo imagery using photogrammetric techniques, largely

automated pixel matching and auto-correlation process that creates mass points of the terrain

surface. The final DTM took the form of mass points. A Triangulated Irregular Network (TIN) was then

created and used for the ortho rectification process.

DTM Accuracy: ±0.8 m @ 68% confidence level in clear open areas (1 sigma)

RGB and RGBI Ortho Rectification Process

OOrtho 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.

The ortho imagery was processed to RGBI to ensure a consistent dataset is maintained for the RGB

and RGBI ortho tiles including the same seamlines. Minimal colour adjustment was undertaken in the

RGB, generally over water areas and along coastal foreshore for colour matching and to minimise

glare.