Clean Airport Layouts

I have blogged about correct airport layouts before, but let me bring the point up again, because it is so important:

• You must create structurally correct layouts (that is, vertices connecting to vertices, not lines) in order to get good rendering in X-Plane.  Just because the preview looks okay in WED doesn't mean your layout is correctly formed!

I wrote some documentation on the scenery site that describes the problems in more detail, with pictures.  

(I've been trying to create more permanent documentation - it is tempting to simply blog the issues because it's so easy to throw a blog post up, but after 110 blog posts in 2007, the scenery site is still very thin on the documentation front.)

Do Not Add Vertices To Make Smoother Curves

I really can't stress this enough: please do not go adding extra vertices in your layout to make bezier curves look smoother in X-Plane.  Why is this such a bad idea?  Let me count the ways!

1. X-Plane will fight you all the way!  X-Plane adds vertices to curves (to make them smoother) when it detects large errors.  If you have a lot of small curves, the errors are inherently smaller and X-Plane will add fewer points.  So the first vertices you add to your curve do almost nothing.  You have to add a huge number of vertices to get a marginal improvement in your curve.  In the meantime...
2. X-Plane will provide variable-quality curve rendering in the future!  Curve detail should be a user-controlled setting.  X-Plane has to run on a wide range of hardware; any time we can let the user pick rendering quality, this is a win, because it helps bridge the gap between the user who just bought a brand new Core 2 Extreme system with GeForce 9800 and the user trying to keep X-Plane 9 running on his G4 laptop which can't be upgraded.  When you add vertices, you take the decision about rendering quality out of the hands of the user, and force high quality on a user who may not be able to handle it. Adding vertices forces a decision of lower framerate on some users.
3. Adding vertices bloats the size of apt.dat.  This is not a huge factor for custom scenery, but is a factor for the default apt.dat.  Robin received a big pile of new airport layouts, and that's great.  But one risk is that the total size of user submitted data could get out of control.  For new layouts made with WED, vertices represent a big chunk of the data.  If you are increasing your vertices by a factor of 5x or 6x to improve tessolation, you are bloating the apt.dat file.
4. Manually adding vertices to smooth curves lowers the level of abstraction in the apt.dat file.  Any time we can have a high level abstract representation of scenery, X-Plane has the freedom to improve rendering in the future.  If your layout is made up of a large number of small curves (instead of a small number of large curves), X-Plane cannot tell that those small pieces make up some larger structure; in the future it may not be able to render those layouts as nicely as ones that are made with fewer control points.

In summary, please use the smallest number of vertices to create your layouts.  (But always add vertices to ensure that your T junctions are correct!)