Palmerston North 0.125m Urban Aerial Photos Index Tiles (2015)

Data Acquisition
The aerial photography for this project was captured within the 2014/15 flying season (September
2014 – April 2015) on the following dates:
12rd ,18th February 2015.

All photography was captured using Vexcel's digital UCE camera and flown at:
0.125m GSD: 7887ft (2404m) flying height
Camera Lens: 100mm

Sun Angle
Minimum of +50 degrees

Urban Building Displacement Specification
Urban 0.125m GSD imagery – The CBD area has been captured with 80% forward lap and 80%
sidelap to achieve near true ortho imagery (near to no building lean).

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 2000 map
projection (NZTM2000) . The datum is New Zealand Geodetic Datum 2000 (NZGD2000). The height
datum is orthometric Moturiki 1953 (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. A final report is generated to check RMSE values are within specification.

DTM Source:
The digital terrain model used for this project was derived from LiDAR DTM data flown
2006 and 2009 and the existing 2012/13 photogram DTM collected by ASL. The DTM data is merged
together seamlessly and accuracy is checked to meet the ortho imagery specification. Note about
updated DTM (if applicable) needs to be added here.

RGB Ortho Specification
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
1:1000 sheet tile layout.