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Georeferencing - Fixing distorted old maps

…so that the modern data (imagery, elevation and GPS) fit properly

MT: Paul I Posted: 10 October 2008, 1:41 PM

NZ Aerial Mapping has great coverage of photography NZ wide, often photos I order are 1-2 yrs old, some are sharper than others. They can supply standard digital images on CD for about $200. Orthophotos are a bit dearer ??? My experience trying to update Beautiful Hills has been interesting if not frustrating… Having access to a Lidar scan layered over an orthophoto showed there were fundamental distortions on the previous map, in the end after trying to make corrections using the old map it became increasingly more neccessary to start from scratch - however it was not easy exercise, the Lidar shows general land shapes very well but no detail at all, a fieldworker needs to put in a lot of blood and sweat to turn it into something usefull. I would say that the Lidar is superior to poor photogrammetry in dense native forest. I read somewhere that there are some new technologies developing which are better than Lidar. If I find the info I'll post it here.

MT: Michael Posted: 10 April 2010, 9:27 PM

The latest OCAD version 10.2.4 has a “rubber-sheeting” option for map transformation. Transformation is when you adjust a distorted map to fit a template you trust (eg an orthophoto). The previous way of transforming is fairly simple, the new way lets you unbend things, and fix a defined problem area while the rest of the map stays the same. Many of our older maps have significant distortion particularly if an addition has been tacked on. There's a “how-to” on the OCAD website which demonstrates the process.

mapping/georeferencedistorted.txt · Last modified: 12:50pm Tue 25 October 2022 by