Thursday, October 30, 2008

Whatever Happened to XES

If you read the original X-Plane scenery web pages, you'll see references to two file formats:
  • DSFs - the files we distribute scenery in.
  • XES - the "X-Plane Editable Scenery" file format, which you won't see very much of.
Here's the story:

When I was first working on the scenery system design, we decided on a pre-processed approach, which implied two types of file formats: pre-baked (editable source data) and post-baked (distributable finished scenery). XES is a GIS container format for the source data.

When we create the global scenery, the process is something like this:
  1. Import lots of data from multiple sources in multiple formats, so that it is all in one giant tile in our format.
  2. Process the data, deriving new information (like terrain type) from existing data (like slope) and fixing problems (like bumps on runways).
  3. Export the data as a DSF, which involves additional conversions (such as converting generic road types to x-plane roads) and DSF encoding.
We keep our raw data partly in XES format, and partly in the original raw format, depending on how slow the importer is - some vector formats are very slow to import (or are not already tiled), so we preconvert to XES. Other formats, like SRTM, are so easy to import quickly that we just use the data as is.

If you have ever tried to use MeshTool, you may have used XES files yourself - the landuse and climate data that MeshTool needs are saved as XES files - it's an easy way to encode a few variable sized raster maps with portable enumeration encoding.

WED does not use XES files - when I started work on WED, I realized that the XES container format was too GIS oriented and not application-oriented, so I created a file format particular to WED. WED will continue to use .wed files, which can contain anything that WED can edit.

In the long term, I don't see XES as being used by anyone except for LR internally; WED will continue to have a WED native format, and we will try to use common simple GIS formats for import/export - most likely SRTM hgt files for elevation and .shp (shape) files for vectors.

1 comment:

dan31 said...

Just let us be able to edit, road, powerline and river a easy way.
I don't mind if my computer must compute all the week end to bake a DSF.