West Coast 0.3m Rural Aerial Photos Index Tiles (2015-2016)

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.