Hawkes Bay 0.3m Rural Aerial Photos (2014-2015)

Data Acquisition:
Aerial Photography was captured using Vexcel's digital UCLp and UCE cameras:
5-6 January 2015, 11 January 2015, 18-19 February 2015, 28 February 2015, 1-2 March 2015, 21
March 2015.

All photography was captured using Vexcel's digital UCLp and UCE cameras and flown at: UCLp 11486ft (3500m) flying height, UCE 18298ft (5769m) flying height

Data Processing:
All aspects of the rural data processing from imagery processing to DTM creation and ortho
production and product deliverables was undertaken in-house by Aerial Surveys.

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
Napier 1962 (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 breaklines
added around water bodies and along major ridges, valleys and areas of steep terrain change such as
coastal cliff areas. The final DTM took the form of mass points. A Triangulated Irregular Network
(TIN) was then created and used for the ortho-rectification process.
Rural DEM – 15,794km2
The rural DTM is automated comprising of mass points only and supplied as tiled files aligned to LINZ
1:5,000 sheet layout as a gridded (10m) DEM in ASCII format.
DTM Accuracy: ±0.6m @ 68% confidence level in clear open areas (1 sigma)

RGB and 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.