Data Acquisition:

The aerial photography for this project was captured within the 2015/16 flying season.

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

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

Camera Lens: 70 mm & 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.

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 for the rural areas was collected from stereo imagery using photogrammetric

techniques, largely automated pixel matching and auto-correlation process that creates mass points

of the terrain surface with further manual editing to remove points on water bodies and minimal

breaklines collected to ensure gross errors were corrected and the DTM generally reflects the terrain

surface. The final DTM took the form of mass points only, suitable for the ortho rectification process.

Rural DEM – 8717 km2

The DTM points were extracted as a gridded (10 m) DEM and supplied as tiled files aligned to LINZ

1:5000 sheet layout. The DEM data is not suitable for contour generation.

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

RGBI Ortho Rectification Process

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 aligned to LINZ 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.