Saturday, July 08, 2006


Distorted images on Geoportail

Now that the French mapping site Geoportail is finally available, I've had a chance to have a quick look round.

As you zoom in, the images show one version of the data (I'm assuming a browser scaled version of the low res data), then replace it with the higher res data. In many places that I looked at, the two images do not line up - leading to a strange image shift on switching between the two.

I wasn't sure what was causing this, but wondered if it was something to do with the images being warped over a 3d terrain model. However, the net effect is simply one of image distortion - if it is a terrain effect, then their model has bad data.

The example image below shows the runway at St Martin in the Caribbean - where as you might expect, a runway is straight, flat, (and in this case at sea level, which should mean no terrain height problems). It's a spectacular runway at the best of times, with landing jumbo jets passing closely overhead of sunbathers on the beach at the end of the runway, but I wouldn't fancy landing on it if it's as uneven as the distorted images on Geoportail suggest!

(I havn't found how you bookmark a particular view using GeoPortail - is it possible?)

St MartinSt MartinHosted on Zooomr

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