Monday, July 26, 2010

Cosmopolitan Trees

I've been playing around with globally expansive trees and noticed some funny behavior of Google Earth. When trees are very large the lines pass though the Earth instead of following the curvature of the Earth. In order to get curved lines I have to use tessellated lines. These are fine, but the altitude of these lines must be "clamped to earth." This means all 3-D structure of the tree is lost i.e. it produces a flat tree along the planet's surface. I have come up with a few ways to solve this issue:

1. Use the 3-D lines for all trees but if they get too large add points along the line to elevate it so it doesn't pass through the earth. One drawback of this is there will be a lot of meaningless points in the KML and it adds clutter to the tree when viewed in Google Earth.

2. Use the 3-D style tree for compact trees and the tessellated lines for cosmopolitan trees. This is the approach I'm partital to using because I think cosmopolitan trees would look too cluttered with the 3-D style.

3. A hybrid system of 3-D lines for the branches that are close together and tessellated lines for far reaching branches. One problem I see with this is attaching a tessellated line to a 3-D line. The 3-D line would have an absolute altitude above the earth whereas the tessellated line would be clamped to the earth. This would add discontinuity to the tree.

4. Create a tree far above the earth's surface with "drop lines" to mark the position of the leafs.

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