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I often use tikz-3dplot to draw pyramid, cone, cylinder,...There is someone say that tikz-3dplot is not 3D Geometry, It is 2.5 D. I cannot explain this thing. Is tikz-3dplot 2.5D or 3D geometry?

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I do not think there is "true" answer to this question. Here is why I think someone could say that tikz-3dplot is 2.5D. To see what that could mean, let is first recall what one may expect from a 3D engine:

  1. Proper projections from 3D to 2D, i.e. the screen.
  2. 3D ordering, i.e. object that are far away get covered by closer objects.

tikz-3dplot provides us with orthogonal projections. They may be thought of as the correct projection in the limit in which the distance of the depicted objects is much larger than their dimensions/sizes. If this is not true, the perspective library provides us with the appropriate projection.

However, tikz-3dplot does not provide us with automatic 3D ordering. So one may say it it only halfway 3D, and one may express this by saying it is 2.5D. Whether or not this interpretation is reasonable is probably a matter of taste.

Programs like asymptote provide us with both proper projections and 3D ordering, and may hence be said to be true 3D engines.

There are some tools available to achieve 3D ordering in tikz-3dplot in special situations, an example is the tikz-3dplot-circleofsphere package, but these solutions are not anywhere as general as asymptote.

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  • +1: For years I wanted to dig deeper into asymptote. Commented Jan 5, 2020 at 5:48

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