MESH, SRTM, DEM & LOD

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MESH, SRTM, DEM & LOD

Postby pete » Wed Mar 13, 2013 4:27 pm

Copied from a previous post by Fly2e

I came across these small definitions and thought I would post them!

MESH is a file which modifies only the relief of a given zone.
A scenery can represent an airport, a city, a building,...
A lanclass modifies the textures applied on the ground.
A afcad modifies the frequencies of airport, radio navigation, the parking's positions, ...


SRTM means Shuttle Radar Topography Mission.
It is one of the mission of the space shuttle, the purpose of which was
to chart the terrestrial relief (90% of emerged world surface).
The data collected at the time of this mission are put has provision of the public.
These data have an accuracy of 90 M (3 seconds of arc),
it is has to say that a point of measurement gives the rise in a square of 90 M with dimensions.
The SRTM are currently the most precise free data.
They make it possible to carry out very great definition meshs, which was impossible
little time ago still.


DEM is the abbreviation for DIGITAL Elevation Model.
the dem files are numerical ground relief representing.
SRTM, GTOPO30 are DEM files.

LOD is the abbreviation of Level Of Detail. The lod is the level of definition that a mesh can represent.
A mesh in lod 9 can reveal details of 76.4 M, in lod 10 it can reveal some of 38.2 M.
while going up of a value of lod, the level of definition is multiplied by 2, the size of the file
increase approximately by 4 (makes some a little less, because of compression).

If the LOD is raised, is the mesh more precise?
No, the mesh precision is only dependent of the the sources precision
Increase the lod will not make the mesh more precise.
the creator use, in general, a lod adapted to the sources precision.
Use a too high lod leads has a loss of FPS.
For the srtm 90 Meters (3 arc seconds), we uses a lod 9, able to represent details of 76.4 M.
The resolution of DEM file is often expressed in arc second.
One arc second corresponds has surroundings 30 M on the equator level .
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Re: MESH, SRTM, DEM & LOD

Postby mikeEmerc » Wed May 18, 2016 9:36 am

Thanks Pete.
I have seen this posted for quite some time,but try to avoid anything that appears to represent anything too 'tekkie (techie)', and that may not hold anything that is of any real help to the average simmer. but,...having been bored,I decided to read it today,and it DOES hold some good info,even for the average simmer (especially those of us who use airport modification and creation programs without really reading all the instructions,and just jump into it,hoping for the best.
Your info JUST might help me figure WHY , when I add some static craft and the like to an already existing airport,the framerate drops like a rock,even if I only add a couple passenger stair trucks or a couple static ac.
Thanks for the consideration in clearing up some of the mystery behind those acronyms.
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