More and more developers of X-Plane add-ons decide to bundle custom-edited terrain meshes with their scenery packages. However, many of these developers aren’t aware of the implications which come with the edit and re-distribution of existing terrain meshes. In this context, Andras Fabian a.k.a alpilotx – the author of the fantastic HD and UHD Meshes – wrote some time ago a great and extensive article. Here I’d like to discuss and extend some of his thoughts, hints and advices for add-on developers. Furthermore, I’d like to make some suggestions for possible solutions.

First of all, editing existing terrain meshes isn’t a trivial task. You need a deep knowledge about the X-Plane scenery architecture, patience and the willingness to bother with undocumented secrets of the X-Plane scenery format – however, it’s possible, as developers of various tools already demonstrated. Also I have developed a tool to edit existing X-Plane terrain meshes, and I offer mesh editing as a service. Further reading in previous articles on my website: about the idea and goals, the current state, and about what’s new and next.

Alright, editing existing terrain meshes is with some knowledge and proper tools not really an issue. The real problems in conjunction with the editing of existing terrain meshes are others, and mostly based on the fact, that the X-Plane World is divided into tiles, measuring 1×1 geographical degrees each, and, that at a certain time only one tile can be active for a specific location – X-Plane uses the tile with the highest priority, defined by the ordering of the scenery packages in the scenery_packs.ini file.

Due it is not possible (yet) to distribute just a local terrain patch, you have to pay attention to the fact, that the custom-edited terrain meshes, which you bundle with your scenery packages, will override whatever meshes your users have installed – and therewith quite likely their favorite terrain mesh for a certain region!

Well, as long the users can only chose between the XP default mesh and Andras’ HD and UHD meshes, you could simply provide an edited version of each of those terrain meshes. However, a lot of additional work – and: What todo, when also another scenery developer offers a custom mesh for exact the same tile? You run into an unavoidable conflict of interests and a situation in which the users have to selectively activate and deactivate custom terrain meshes, depending on the airport scenery they head for – not very user friendly!

Another aspect that you should be aware of, is that the users of photo meshes grow, especially since the fantastic tool Ortho4XP is available. Due Ortho4XP offers the option to feed “patches” into the Ortho4XP-triangulation, I don’t recommend to patch an existing Ortho4XP-mesh with other tools than Ortho4XP itself. As a scenery developer, you could offer with your scenery package, in addition to a custom mesh for users who prefer a land-classification based mesh, also an Ortho4XP-patch for users who prefer photo meshes – however, the amount of terrain mesh possibilities may confuse the users!

Last but not least a very important thing that many forget: As long as we haven’t the option to share and apply terrain patches automatically, keep in mind, that you need for the edit and re-distribution of an existing terrain mesh the permission from the original mesh author. That’s Laminar Research in case of the X-Plane default mesh, and in the case of the HD and UHD Meshes you have to contact Andras Fabian a.k.a alpilotx!

Conclusion: A lot of circumstances that speak against the current procedure, to bundle entire terrain mesh tiles with scenery packages, just to customize the terrain locally. Already with the start of the development of a new tool to edit existing terrain meshes, I stated to aim not only for another tool to edit existing X-Plane terrain meshes, but also for the following goals:

• For developers: An official terrain patch specification and a common terrain patch repository, as well as a toolset to create and edit patches – in the best case integrated in the tools add-on developers already use => The idea is to use Laminar Research’s WorldEditor (WED) for this purpose and the existing Airport Scenery Gateway to share the terrain patches.
• For endusers: Upon the basis of the common terrain patch repository, an – in the best case fully – automated approach to patch the terrain meshes, whichever the endusers have installed => The idea is to apply patches – if not possible at runtime – whilst starting X-Plane or running the X-Plane updater.

Some of these tasks are already realized, others need a further discussion of technical and organizational aspects. Others in turn require the cooperation of Laminar Research (LR). We all know, LR has other priorities at the moment, but I thought, that we can convince them, when we prepare and share with LR an extensive specification of the desired solution. Independently, the work on the tools, which are independent from the X-Plane core application and updater, can be forced – for example the terrain patch editor, integrated into WED, in conjunction with the finalization of the terrain patch specification.

If you have proper knowledge of the X-Plane scenery architecture, in particular the Distribution Scenery Format (DSF), and are willing to contribute, then do not hesitate to contact me. I’m looking forward to your feedbacks and opinions.