Hamilton 0.1m Urban Aerial Photos (2016-2017)

Data Acquisition:
The aerial photography for this project was captured within the 2014/15 flying season (September
2014 – April 2015) on the following date:
20 March 2015.

All photography was captured using Vexcel's digital UCLp camera and flown at:
0.10m GSD: 3850ft (1173m) flying height
Camera Lens: 70mm

Sun Angle
Minimum of +40 degrees

Urban Building Displacement Specification
Urban 0.10m GSD imagery – using the UCLp camera and by flying with 60% forward overlap and
with 30% sidelap (standard stereo coverage), maximum 1.1m building lean per 3m height within the
image model area.

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 Auckland 1946 (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 2008 and 2010 LiDAR
DTM data. Outside the existing data we have collected a new DTM from the stereo imagery. The
DTM data is merged together seamlessly and accuracy is checked to meet the ortho imagery
specification.

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.