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FlyingDemon

Screen Space Error for ROAM?

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I've been working with the ROAM algorithm for large terrains and I've read in several places about a error metrics. I know that they're used to check if something needs to be split or merged, but what exactly is a screen space error metric? The area of the screen that a specific ROAM triangle occupies or something else? If it is, or isn't, how would I calculate it?

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The metric is simply the distance (in pixels) between the location of a vertex and the location of the same vertex when the triangle is not split. If distance is greater than the threshold value, you split the triangle.

Ideally, you compute the distance in pixels by transforming the locations of the vertex into screen space. But that is computationally expensive, so you might optimize the test by computing a world space threshold value that depends on the FOV and screen resolution, and then check the distance in world space.

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