Scenery Systems

[inktomi]

I've been thinking about how scenery systems actually work, but I can't seem to figure out exactly how they do.

It seems like the most common way to create terrain from scratch in a video game is via a height map, where black is low and white is the highest terrain on the map. You can create such height maps from USGS data that's freely available, so it seems like a reasonable approach... you'd just load the "next grid" as the plane approaches it and then unload the one behind you as you pass by.

Does XPlane work like this... loading a grid of height maps and showing you the one you're currently inside? Is there a different way that this all works?

I know this isn't really a "how to make scenery" question, but I've always wondered.. how does a flight simulator show accurate terrain for the real world without having to put a huge amount of stuff in memory.

How does it all work?

[tkyler]

currently, the terrain is "built up" of raw datapoints of elevation. These points are then connected to make triangles which make the terrain. The source of the datapoints can be in many forms, but as you mention, a "height map" or "digital elevation map" or DEM is readily available and fairly common. The terrain is not built "on the fly" from these sources but is pre-built and stored in the DSF files and this makes up the bulk of the data on xplane discs. The process of creating the DSF terrain files from image or other sources is what we call "cutting DSF tiles" and it takes a LONG time to do for the entire world....a few days maybe?

You are correct that xplane loads and unloads grids as you fly...at any given time, there are six of these grids...also called 'tiles" loaded at one time and they load in front of the plane as it flies. In the future, we hope to incorporate image based dynamic terrain generation or dynamic 'tesselation as it's called. This means we can load up lower resolution terrain in the distance and then have it get more detailed as you get closer to it. The technology exists now, but getting it incorporated and performing well will take a while. As cool as the video below is.....still, the world is a pretty big place and harnessing and managing data to make it all look like that is no easy task. A small area like that...that is generic....sure, no problem. The whole world? that's something different altogether.

Edited December 22, 2011 by tkyler