# QMID question

#### GaryGB

Hello:

A LOD-13 / QMID-15 "Quad" has 256 x 256 "Area Points", each capable of having a unique assigned altitude value.

[EDITED]

Notice that the 'span' size of Quads increases with distance above the FS ground surface (the maximum navigable Altitude of FSX is 100 Million Feet).

The Geographic Arc Degree span sizes for each Quad / Area Point level is of course a fixed value for each location on the FS 3D spheroid world model as given in the FS SDK documents.

Note as well, that Quad side dimensions vary with their position on the FS 3D world sphere / Geoid, and (reportedly) only approach an equilateral or "square" shape at a specific North Latitude:

https://www.microsoft.com/Products/Games/FSInsider/developers/Pages/GlobalTerrain.aspx

A hypothetical FS 3D world spheroid scale model (1 Millimeter = 1 Meter)

FYI: Some additional pertinent "white papers" on FS scenery development rendering:

...and an inquiry which (indirectly... for me, at least) raises the question as to whether certain FS scenery placement calculations are performed "solely within FS SDK internal compiler formulas" to adapt WGS84 coordinates to what 'may' actually be a purely spheroid FS 3D world globe model:

[END_EDIT]

GaryGB

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#### fs1

Hello:

A LOD-13 / QMID-15 "Quad" has 256 x 256 "Area Points", each capable of having a unique assigned altitude value

GaryGB
Thanks Gary. That I was I needed. The other LOD Level Quads have the same 256x256 area points as well? Let's say LOD-11 ?

#### GaryGB

AFAIK, yes... all the way up LOD-27 / QMID-29.

BTW: Considering that Area Points may be regarded as "mini-Quads", that would raise a question as to whether there are actually Quads that are LOD-37 / QMID-39 !

ex: LOD-13 + 10 = Lod-23 Quad size of Area Point

Hypothetical extrapolation:

ex: LOD-27 + 10 = Lod-37 Quad size of Area Point (0.00029296875 Meters grid interval = 0.29296875 mm between data points)

One might wonder if the FS run time rendering engine is actually able to resolve such small values !

[EDITED]

CAVEAT: The extent of Meters on the ground mapped by draped aerial imagery texture pixels (aka "Texels") varies by FS Terrain Grid Quad / Area Point position on the FS 3D world spheroid / geoid.

The extent of Meters on the ground typically discussed are for a "theoretical" maximum quad "X" (Longitude) dimension of 1,023 Meters on the ground at ex: the equator of the globe.

NOTE: The extent of Meters for Quad / Area Point span increases with AGL Altitude to the FS theoretical maximum Altitude of 100 Million Feet.

Actual constants of measurement associated with the FS Terrain Grid Quad / Area Point extents is "Fractional Arc Degrees" on the ground (...and in the air up to FS theoretical maximum Altitude of 100 Million Feet).

[END_EDIT]

One might wonder how small terrain grid vertex intervals are rendered ...even if LODs are capped at LOD-27 ?

Welcome to Microsoft "Molecule Simulator" ('small world', isn't it ?)

Hope this helps a bit more !

GaryGB

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#### fs1

Thanks GaryGB

One might wonder how small terrain grid vertex intervals are rendered ...even if LODs are capped at LOD-27 ?

GaryGB
Well this shouldn't be 1/256 of the block size of LOD-27 ? Each LOD shouldn't have 256x256 indivisible altitude quads?

Also the intervals are not tied to the lowest possible meter/pixel ratio? What is the sense of doing something smaller if in screen will be topped by this limit ?

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#### GaryGB

These questions certainly form a compelling basis for further "testing" by FS developers and end users alike.

You may wish to load a terrain mesh BGL into FS SDK TMFViewer, with (2) different LOD and QMIDs active in the on-screen terrain grid display, while performing repeated zooming in and out via the NumPad <+> and <-> keys.

BTW: LOD + 2 = QMID

FYI: FS2004 (aka "FS9") was capped at 4.6875 (aka "4.8"; ...or as Dean Mountford insisted, "4.75") Meters on the ground per pixel resolution for 256x256 pixel tiles of aerial imagery draped onto Area Points of LOD-13 quads within the via FS2Kx SDK Resample.

Run time rendering of terrain mesh vertices in FS2004 version 9.0 was originally capped at 76.4 Meters, and was increased to 19.1 Meters on the ground between elevation data points ...per end user requests in FS2004 version 9.1 (aka "FS9 Update").

In either FS v9.0 or 9.1, end users could still output higher resolution FS terrain grid elevation data points in BGLs via FS2Kx SDK Resample, however the FS run time rendering engine would render only a super-imposed slope shadow to "simulate" details for terrain detail above that otherwise rendered at the maximum internally-'capped' resolution Meters on the ground between elevation data points.

FS2002 (aka "FS8") actually was capable of run time rendering of higher resolution FS terrain grid elevation data points than FS9.

NOTE: FS run time limitations of vertex and texture display via the FS terrain grid must be distinguished from that which is otherwise virtually 'un-limited' ...when rendered via SCASM / ASM Ground Polygons and/or 3D MDL objects.

GaryGB

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