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Posted 19 November 2012 - 06:58 AM

The accuracy problem will probably have to do with floating point accuracy. Floating point values can store a large range of values, but their precision will deteriorate the more they stray away from 0. This is because floating point values are normally determined by a mantissa and an exponent (Note: I'm simplifying things here for clarity purposes), so they can be a good solution for doing calculations with small numbers (as smaller numbers tend to be 'more precise' in most cases), but they can show some heavy precision errors for larger numbers.

So the larger a map gets the larger your co-ordinate values can become and the more precision issues you'll encounter. If a distance unit in your game corresponds to a small real world unit (eg. 1 unit = 1 cm) your precision will become even worse for larger distances.

Then there are also the issues that a larger map means probably more memory usage, more bookkeeping, longer load times, in-game stalling (when doing streaming) and maybe longer frame update times (although well-designed scene systems shouldn't have too much trouble with this).

It's not impossible to do really large maps, but it will require some trade-offs and some different design decisions, and maybe the engines you mentioned just don't have a need for really large maps.

EDIT: Ninja'd again...

Posted 19 November 2012 - 06:56 AM

The accuracy problem will probably have to do with floating point accuracy. Floating point values can store a large range of values, but their precision will deteriorate the more they stray away from 0. This is because floating point values are normally determined by a mantissa and an exponent (Note: I'm simplifying things here for clarity purposes), so they can be a good solution for doing calculations with small numbers (as smaller numbers tend to be 'more precise' in most cases), but they can show some heavy precision errors for larger numbers.

So the larger a map gets the larger your co-ordinate values can become and the more precision issues you'll encounter. If a distance unit in your game corresponds to a small real world unit (eg. 1 unit = 1 cm) your precision will become even worse for larger distances.

Then there are also the issues that a larger map means probably more memory usage, more bookkeeping, longer load times, in-game stalling (when doing streaming) and maybe longer frame update times (although well-designed scene systems shouldn't have too much trouble with this).

It's not impossible to do really large maps, but it will require some trade-offs and some different design decisions, and maybe the engines you mentioned just don't have a need for really large maps.

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