In past posts I have tried to describe the implications of DSF base meshes, which are “fully baked”. The basic idea is: the base mesh is fully formed ahead of time as a single unit. This is a trade-off:

  • The advantage is performance. The sim has no work to do except draw that base mesh as fast as possible.
  • The disadvantage is flexibility. The sim has no easy way to modify that base mesh.

By comparison, DSF overlays are not fully baked – you can add 8 overlays to an area and they will all run on top of each other. There is a real performance cost to this. Compare the performance of a huge number of draped orthophotos (via .pol files, an overlay technique) with a real orthophoto base mesh cut with MeshTool. You’ll easily get 100 fps on the DSF base mesh, but you won’t come close with the overlay.

If you want to compare X-Plane to a first person shooter, consider the “cost” of overlays as one of the reasons why FPS games appear to be higher performance than general purpose flight simulators like X-Plane and MSFS. In a FPS, each level is likely to be fully baked, with only one level loaded at a time. This is equivalent to X-Plane’s DSF base mesh. The FPS game doesn’t need to manage overlays that are put together at runtime in unpredictable combinations, and this lets the FPS engine optimize for performance.

(In fact, the FPS engine might be able to optimize a second way, if third party level packs are not available. Not only can a level be ‘fully baked’, but it can be fully baked specifically for that particular rendering engine. By comparison, a DSF base mesh will run with X-Plane 8 or 9 – clearly it isn’t specifically optimized for just one version of X-Plane.)

If you look at the scenery system “overview” I wrote around the time of X-Plane 8’s release (this overview is now pretty out of date; I really need to update it) you’ll see this:

There are now two scenery formats – one for editing and one for distributing scenery. Both are new.

DSF stands for “distribution scenery file” – the idea is that DSF was meant to be a container for fully baked finished scenery, optimized for small size on DSF and fast loading, but not editing. Our internal tools use another file formatm “.xes” to contain imported global scenery data before it is baked. Originally I thought that we would provide an editor to .xes files, but that has not happened. With MeshTool, you provide input data in more common public formats like SRTM HGT or GeoTiff, and .shp (shapefiles). You can think of .shp and .tif as the editing formats for MeshTool and base DSFs.

So how do we make it easy for users to edit scenery? I believe OpenStreetMap is the answer. The common request we get from users is for a way to edit the vector source data for global scenery (or sometimes, the request is to edit the features created by vector data). In other words: how does a user edit the coastlines, water bodies, and roads? With OpenStreetMap, OSM itself becomes the “editing” format for X-Plane scenery with DSF as the final result of baking.

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.

3 comments on “Baking and Overlays

  1. With big bandwidth getting ever cheaper, are we already to the point where "open scenery" on the web could be doable (at least technically).

    The idea is to have providers of scenery, on the web, in a format the sim can download. Cached locally, of course, and possibly converted into the sim's native format. And then you tell your sim, "I want my global textures from these guys, and the "pretty good global airports" from these guys, and the "really awesome Arizona airports" from these guys. Whenever those guys update their scenery, you get (either automatically, or when you tell your sim to check for new scenery) the changes downloaded and compiled into the local cache and you go flying. This would make it much easier to get updated add-on scenery.

    The scenery providers could be pay or free, or both.

    I imagine (or perhaps just hope) that there would be a place for "scenery compilers," people who are not creating scenery but who are hosting compilations of open scenery that they have vetted, and that you could, with little fear of disastrous results, add to your sim's list of "places to get scenery from." These people would be performing the same role as the editor of a story anthology, only for scenery. Some editors would get reputations above others. Think of Ted's airports, but not as a place you got to download airports. Instead, it's a place you tell your sim to go to download airports.

    Find a way to get another sim maker to buy into the open format, and it's possible that sim makers could eventually get out of the creating-scenery business altogether.

    I don't discount the sweat it would take. Creating an open format that more than one sim can use (or derive their internal format from) seems like big work (and polly ticks). And if I've learned anything from reading your blog, it's that every design decision you make has a hundred and one consequences you never could have imagined. But at least as a waving-my-hands-around kind of idea, it sounds cool, doesn't it?

  2. I'm one of those people who would love to spend their time making contributions to the X-Plane community in the form of fixing meshes. Lakes, rivers, channels, islands, and mountains are all essential parts of navigation in the part of AK where I am. I was hopeful when I upgraded from V8 to V9 that the mesh would be better for my area, but instead it was worse. I've since used satellite imagery from sources such as Google Maps and USGS to at least correct the imagery. I would be very happy to be able to correct the mesh in my neck of the woods and I'm sure others would be glad to do the same to their area of choosing. Hopefully these opportunities will appear sometime within the nest few years. It would be wonderful Thanks for all you do.

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