One of the main differences between FS2004 and FSX when it comes to rendering the earth, is that FS2004 assumes that the earth is locally flat while rendering the scene, while FSX uses the correct curvature of the earth as well. But this has some consequences for scenery designers. When you make ground polygons they are usually flat in the design tool, but putting them on the curve of the earth will mean that the ends will float in the sky. The ground polygon wizard of ModelConverterX does correct for this problem, by shaping your ground polygons to follow the curve of the earth.

But this problem not only affects ground polygons, also normal buildings or animated vehicles can have this problem. Therefore an experimental function to correct for this problem was in ModelConverterX for a while already. Over the last week this function has been expanded and improved and therefore it now has become a new editor: the Earth Curve Editor. You can load this editor by clicking on the icon with the picture of the round earth.

From this editor you can set the position of your object and choose what you want to correct. Entering the exactly altitude of the ground is very important to get the correct correction.

A problem in FSX noticed before is that attached effects are offset from the geometry, the further you get from the reference point. This is related to the curve of the earth as well. So there are two chooses for a correction:

1. You correct the geometry to follow the curve. This will also correct the path of the animations and attached platforms. Attached objects, like effects, are not corrected however. Once the geometry has been corrected they line up again.
2. You only correct attached objects, like effects. This correction will move them to line up with your geometry. But if your geometry is big, it will still float at the end. So in general it is probably better to use option 1 instead of this one.

This new editor is in the latest development release. I hope it proves to be useful and let me know if there is any feedback.