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LINZ releases post Christchurch earthquake aerial imagery to public
Media and the public can now access the same aerial imagery of Christchurch that Police, Civil Defence, and other emergency responders have been using to assess damage to the area.
The imagery of the city was taken on 24 February, and clearly shows the extent of the damage from the 22 February quake.
As the country’s national mapping agency, Land Information New Zealand (LINZ) is coordinating the release of this imagery on behalf of the Crown, on the authority of the National Controller.
Civil Defence National Controller, John Hamilton, commissioned the aerial images to help inform the work of the Christchurch Response Centre (CRC).
LINZ has released the imagery under a Creative Commons Attribution 3.0 New Zealand license. This means anyone is free to copy, distribute, and adapt the imagery so long as it is attributed to the Crown.
The imagery was collected by New Zealand Aerial Mapping (NZAM) flying at 1,600m above the ground using a Vexcel UCXp large format digital aerial camera.
“It’s important to remember that this imagery is a snapshot of the way Christchurch looked a couple of days after the earthquake. It’s good that this information is now available to all of New Zealand and the world.” says Geoff Howard, New Zealand’s Chief Topographer.
Media enquiries: Victoria Dew, Land Information New Zealand, phone +64 4 496 5402, mobile +64 27 222 9566, email firstname.lastname@example.org.
About LINZ’s work in this area
LINZ is responsible for collecting, maintaining and managing authoritative national mapping records, and we’re currently working on how the collection and sharing of nationally significant datasets and imagery can be better coordinated.
About the Christchurch Response Centre (CRC)
The CRC is based in the Christchurch City Art Galley and is the emergency centre co-ordinating all activities necessary to respond to the earthquake of 22 February. It houses the National Controller and the other agencies responding to the emergency, including the Christchurch City Council, Ecan, emergency services, lifeline utilities, and support organisations.
Technical information about the imagery
Summary of data
This dataset was produced by New Zealand Aerial Mapping (NZAM) to support the response to the 22 February 2011 earthquake in Canterbury. It is a complete collection of the 10cm GSD orthophoto tiles.
The photography was collected flying at 1,600m above the ground using a Vexcel UCXp large format digital aerial camera. The photography was acquired on 24 February 2011 between the hours of 11am and 6pm and has a ground resolution of 10 cm.
To support the georeferencing of the photography a GPS base station receiver was operated at a temporary survey mark that NZAM established at Christchurch Airport.
In order to expedite their production, these orthophotos were produced using a number of shortcuts that would not be followed for a fully specified orthophoto project.
The aerial photos position and orientation (POS) were determined using the POS observations collected at the GPS base station and in the aircraft. This data was processed using New Zealand Geodetic Dataum 2000 (NZGD2000) reference system. A coordinate for the base station was computed using single baseline processing and data supplied to NZAM by GNS Science, from the PositioNZ station MQZG. Given the magnitude of the earthquake it is likely that the location of MQZG has changed. However, as no information was available at the time the photos were ortho rectified (made into a photo map) it was assumed that the coordinate for MQZG had not changed.
For the orthophoto generation NZAM used a Digital Terrain Model (DTM) sourced from within its archive. This DTM was not edited or checked for change.
Automated mosaic seam line placement was used during the orthophoto production. NZAM chose to use a simple ‘most nadir’ algorithm for their placement. This selects the most central portion of each available photo and thereby helps minimise the amount of perspective view lean on buildings. The seam lines can be clearly seen on some of the photography.
The geodata is all in terms of the New Zealand Transverse Mercator 2000 map projection.
This imagery is available to view or download.
Given the emergency, the orthophotos have only had a cursory review. Given that the DTM was not updated and checked it is likely that the orthophotos will include areas were the imagery appears smeared or is out of position.
While NZAM endeavoured to collect cloud free photography of the area within one day, there is the odd puff of cloud and cloud shadow in the imagery. This does not significantly impact on the usability of the photography for the earthquake response work.