The problem with KLGA

With X-Plane 820 global scenery, you can fly with "sloped runways" (this option drapes the runways like a piece of cloth over the terrain no matter how strange the terrain is) at most locations, but not La Guardia, where there is a huge hump in the runway.

It turns out the problem with KLGA is that there are vertices in the mesh that are adjacent to both water and the airport. The field height is a few meters above sea level, so we cannot decide what height those vertices should be? (Zero for the water, or a few meters for the airport?) In the 820 global scenery, the water wins, pullling down any part of the airport that is coastal.

For the version 9 re-render of the global scenery I am trying to fix this by creating a buffer zone of a few meters around coastal parts of the airport. This assures that we will have at least TWO vertices at the corners of the airport. The inner one can then be at field level and the outer one at sea level. The triangles in between these two "rings" form a sloped transition area (more sloped if the airport is far above water level), allowing the inner area to remain flat.

We'll have to see how much this helps coastal airports - in hindsight I'm surprised that a lot more airports weren't as unmanageable as KLGA.

(As a side note, it appears that the SRTM raw elevation data is at its least reliable in airports - there's something about them, perhaps the metal or concrete or heat that causes a ton of drop-outs and false reflections. So we have to pre-process the airport areas pretty heavily to use them at all - and sometimes this pre-processing doesn't even work)