With X-Plane 860 there are two ways to draw stuff on the ground:

  • Use an OBJ and ATTR_poly_os. This is the way most people have built custom taxiways, markings, etc.
  • Use a DSF overlay with a bezier polygon (which is controlled by a .pol or .lin file).

Which should you do? Hrm…

  • For any geometry that goes over a very large area, the DSF overlay with a bezier polygon is basically a requirement, because the polygon will “drape” over the ground. The OBJ might just stick out in the air.
  • If your element repeats a lot, the OBJ may save memory. (OBJs are stored in memory once and used many times – bezier polygons use RAM each time they’re used.)
  • If the overlay is very simple, the DSF overlay may perform better.
  • It may be too expensive to build complex lines with DSF overlay lines. They’re meant for taxi-lines, not full vector graphics!

So here are a few decisions I’d make:

  • Taxi lines – certainly DSF overlays if we’re not using apt.dat 850.
  • Parking spot at an airport – use one large polygon with a texture, not a bunch of bezier lines.
  • Use a DSF overlay for that parking spot, even if we use it 60 or 100 times. The simplicity of the overlay (vs. the compexity of starting and stopping an OBJ from drawing) outweighs the cost of using it many times.
  • A very structurally complex overlay on the ground with thousands of triangles (that for some reason cannot be created with a texture) that is used a lot — well, this is an “artificial” case I’ve made up, but in this case use an OBJ.

About Ben Supnik

Ben is a software engineer who works on X-Plane; he spends most of his days drinking coffee and swearing at the computer -- sometimes at the same time.