Outerra Engine > Technology
Planetary Engine in detail
cameni:
--- Quote from: Aleksandar ---
--- Quote ---No I didn't write any paper on it, I'm not skilled in writing academic papers (I never tried ;)).
--- End quote ---
But you should try! ;)
Practical approach, skills and ideas you have should be published as an academic paper.
--- End quote ---
Well, I might write one about the approaches and results after it's done. But I have yet many things planned to do there, and the blog format suits me better now. But I should probably put more technical details into it, since there are still more people asking for it.
Do you work in academic field?
Aleksandar Dimitrijevic:
Fortunately, or unfortunately, I do work in academic field. :)
I'm also involved in many scientific and non-scientific projects. Those programming and fulfilling customers' requests dragged me out from the computer graphics and finishing my own terrain rendering algorithm. But, slowly I'm coming back...
I'm glad that you have started your blog and this forum. It is always very useful to exchange ideas with people doing the same thing. Especially, when someone is alone in his effort to do something, like I am.
Thank you for the previous answer about tile's coordinate system! I was blind as a mole, thinking that all tiles in the matrix must be in the same coordinate system, or I'll have problems with bounding areas. I'll try to change drawing "philosophy", by I first have to test the implications of translation of tens of thousands of tiles on the drawing speed. I hope that impact is not significant.
Another very interesting question about rendering the whole globe is In which coordinate system your DEM and raster data are? Having LatLon coordinates dramatically alleviate gathering data, but there are singularities at poles. Even a mighty GoogleEarth have problems with poles. Fortunately, only a small number of people (only those who knows about the problem of rendering the whole Earth) can notice that. :)
cameni:
--- Quote from: Aleksandar ---Another very interesting question about rendering the whole globe is In which coordinate system your DEM and raster data are? Having LatLon coordinates dramatically alleviate gathering data, but there are singularities at poles. Even a mighty GoogleEarth have problems with poles. Fortunately, only a small number of people (only those who knows about the problem of rendering the whole Earth) can notice that. :)
--- End quote ---
We used LatLon coordinate system initially but because of the problems with poles or rather because of problems with the mapping in general we abandoned it.
Currently we are using something called "quadcube" - cube projected to a sphere, with quadtree for each cube face. Quadtree vertices can be simply projected to the surface of the sphere, although we ended up using a slightly more complicated projection that tries to compensate the distortion appearing there.
As the result we have to remap all raster data to this system while simultaneously compressing and generating LOD layers. It is a relatively slow process, but the resulting data organization is extremely LOD streaming-friendly and rending is then fast and straightforward. Likewise, continuing with fractal noise refinement from the tile level where the elevation data end is natural too.
Aleksandar Dimitrijevic:
I had the same idea, but instead of remapping the whole world, I had used LatLon mapping from -45 to 45 degrees (Latitude), which is used for the four sides of the cube, and remap the rest in two plates (top and bottom side of the cube). Of course you did it better. :)
Thank you for the explanation! Currently I am implementing texturing in the new limited area application and Earth-Cube will have to wait some other time for the implementation. ;)
Something related to the previous post...
I have just tried to express each tile (block) in its local coordinates and translate it to the original position on the globe, and ... IT DOESN'T WORK. :(
There are gaps between tiles, as I had assumed, and drawing is significantly slower (PushMatrix/Translate/PopMatrix). So, I'll try to find some other solution. At one moment it seems like it could work, but...
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