Data Acquisition:

The aerial photography for this project was captured on 20 March 2015.

All photography was captured using Vexcel's digital UCLp camera and flown at 3850ft (1173m) flying height.

Data Processing:

All aspects of the data processing from imagery processing to DTM creation and ortho production

and product deliverables was unadertaken 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). The products are tiled into NZTopo50 map sheet

tiles as noted below.

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 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 extracted aligned to LINZ

1:1000 sheet tile layout.

Spatial Accuracy: ±0.2m @ 95% confidence level in clear open spaces (2 sigma)