Definitions

Resolution

The distance between data points on a regular grid in the source data, compiled terrain mesh scenery, or the vertices in the terrain scenery when displayed in Flight Simulator.  Posting

You will notice references to actual resolutions on this page are all approximate, e.g. ~19m (approximately 19 metres). The reason for this is given below if you wish to delve more deeply, but for the purposes of understanding the main issues on this page, you can if you wish skip the next paragraph completely.

The actual measurement of resolution is in degrees of latitude and degrees of longitude. The resolutions quoted in metres are just handy approximations to what would otherwise be fairly meaningless looking decimal fractions. The actual resolutions differ when measured between adjacent points in the North-South direction and between adjacent data points in the East-West direction. These latter also vary depending how far North or South of the Equator you are.

LOD

A term that inevitably crops up in discussions of terrain mesh scenery is LOD. This stands for Level Of Detail, with successively higher levels of detail corresponding to (usually) a doubling of resolution. Graphical applications typically use different levels of detail to allow the same object or feature to be displayed at higher resolutions closer to the viewer and at lower resolutions further from the viewer. This makes the rendering software more efficient as it does not have to waste time and resources displaying levels of detail that the viewer simply cannot discern at that distance in any case.

The relationship between LOD and resolution in FS2002 and FS2004 is illustrated in the following table:

The use of the term LOD usually implies the presence of different levels of detail at difference distances, and there are various schemes such as CLOD or terrain-mip-mapping for implementing this. The precise nature of the scheme used by Microsoft to implement multiple levels of detail is not known. It has close similarities to some of the published schemes, but is likely to be a proprietary implemention unique to Microsoft.

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