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Introduction to Geo

‘Geo’ is a project that I started after growing a little frustrated with my previous project ‘Isis’. Isis was an attempt to create a virtual island and explored such techniques as clip-maps and geometry shaders, over time though I realised that a single island was too limiting and I would rather have a complete planet to create procedurally – and if you are doing one planet you might as well do more so Geo is an attempt to produce a simulation where you can move from being in space moving between planets right down to being at ground level walking around.

I’m still focussing on offline procedural generation as I want to create environments at a fidelity and diverseness that simply cannot be generated on the fly at runtime but with the amount of data needed for potentially thousands of planets a caching and background generation system needs to be built in as a core part of the systems architecture. The first version uses worker threads on the same machine (via a task pool system) but I’m attempting to design it in such a way that a distributed work system can be utilised to provide far more computing power for the procedural environment generation.

Other major differences between Isis and Geo is that I am not using clip-maps this time for the terrain as I want to experiment with fully 3D terrain meshes rather than being limited to a traditional (and simplistic) height field, my planets are thus constructed using a terrain density function evaluated using the marching cubes algorithm with individual sections of geometry stored and rendered using an octree allowing any possible shape to form such as vertical cliffs, overhangs and cave systems. I have a vision in my mind of a blasted half-planet, it’s entrails flowing into space the result of some cataclysmic impact, would be nice to get there if I can.

One of the major problems to overcome when trying to simulate such a large environment of course if the issue of numerical precision. Single precision floating point numbers as are typically used for 3D graphics can only store about six significant digits and so quickly run out of precision when you are talking about representing features all the way from the centimetre scale right up to astronomical units and beyond. To combat this, Geo uses a number of different co-ordinate spaces each with it’s own origin and scale – planetary bodies are generally represented at the kilometre scale with the centre of each cell in the octree structure providing a convenient origin for it’s content. This way as we progress down the levels of detail the range of values naturally diminishes and accuracy increases. Flying between planets in a solar system however may require representations at the astronomical unit scale with the origin at the centre of the solar system – managing the smooth transition between these different co-ordinate spaces is paramount to eliminate popping/snapping artifacts and ensure maximum accuracy in the geometry rendering.

There are many other problems both large and small presented by attempting a simulation of this scale but the whole point of the exercise is to experiment and without the pressures of work the project can drift quite happily at it’s own speed and the focus shift with my mood. With that in mind progress so far has been fairly slow as I scrabble to find the odd half-hour here and there to work on it but what is there so far I think is quite promising. I’ve added some early screen shots to the Gallery section to record it’s state so far – the lack of atmospheric scattering, dynamic shadows and surface detail makes them a little on the bland side but I want to record progress and it has to start somewhere.

Anyway, that’s probably enough for now – have a look at the screenshots and subscribe to the Geo Blog RSS feed if you are interested and want to be notified of future updates as they get posted. Use the forums to leave feedback too if you like – it’s always good to hear from the community.

– John

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  1. January 4, 2011 at 12:33 pm

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