I'm very new to anything concerning GIS so please forgive me if this question has been asked before, but I assure you, I've been trying to find an answer for quite some time now. Of course it is possible, that the question itself is dumb or that I've overlooked the answer because of my lack of expertise in this field.
I built a programme for a 3D Engine that reads latitude and longitude values from an openstreetmap (osm) file and projects these onto a x/y plane. With the projected corner points of buildings I then create rudimentary 3D buildings by just extruding their ground areas. I used two projections so far, the Mercator and the UTM projection.
Now I'd like to "download" satellite images (or rather make screenshots from Google Maps / Earth) and use the as an underlay, so that the constructed buildings sit on top of the image in the right places and the right scale. I'd like to be able to align the buildings with the buildings on the satellite image by doing no more than the following three actions (since I have to do it manually):
- Moving the image in the x/y plane
- Rotating it around the z axis
- Scaling it (maybe independently) in x and y
I cannot, however, distort the image in any other way. I know that with each projection you have a tradeoff, as there is no projection that is equidistant, isogonal and where the area proportions are correct all at the same time.
With the two projections I've used so far it wasn't possible to align the image with the buildings, since as soon as I made it fit in one place it didn't fit in other places any more.
So my question is, which projection I should use and which properties the projections needs for my purpose. As I see it, a satellite image (if what you get from Google Maps / Earth even is from a satellite) is a projection itself, so is there are projection that is similar to what a satellite sees when orbiting the earth?! Are there any others sources for satellite images that would work better?
Thanks in advance!
P.S. The area covered by the osm file is rather small (around 3km x 5km).
Best Answer
The EPSG code used for Google map image (if you see buildings, it probably comes from aerial images) is : EPSG 900913 (EPSG is a standard naming convention for reference system, this one is easy to remember because it writes "google")
UPDATE : As mentioned by mkennedy, the "official" EPSG code for this projection is EPSG 3857
What is the difference between EPSG:900913 and EPSG:3857?