LOD11 span in metres - Urgent!

[Guest Stormshadow]

Hi everybody,Does any1 know exactly what the width and height of an LOD11 cell are in metres?SDK says the span for LOD11 is 4892m - But I believe the cell is not a perfect square or is it?CheersStorm

[Guest Stormshadow]

Assuming that the 4892m value specified in the SDK is the Width (horizontal length), using the Lat and Long deg boundaries for an LOD11 cell, I came up with a height of 3669.00m. Thus an LOD11 cell would be:4892m (L) x 3669m (H)Is my maths correct?Storm

[Guest Stormshadow]

The value I calculated doesn't convince me...any ideas?

[arno 1]

The size depends on where on the earth you are, the closer you come to the poles the smaller they are. So your question can not be answered without knowing where on the world you are.

[Guest Stormshadow]

Can't I use the N,S,E and W coordinates of the particular cell to calculate the span in m's in some way? These coordinates are easily computed through LOD calculator...Storm

[arno 1]

Yes, that should be possible. Let me think LOD11 means that the earth is split in 6144x4096 squares (I hope I counted that correct). So that would give:height = R*pi/4096width = R*cos(lat)*2*pi/6144where R is the radius of the earth, so circa 6378000 meters (if I remember correct).

[Guest Stormshadow]

Hmm, I'm not on the same wavelength :)What I did is find the difference between the N and S coordinates of the particular LOD11 cell. Same thing for the E and W points. I then scaled these using the Lat and Lon deg values given in the SDK table for LOD11. But for this cell I came up with practically same values of 4892m x 4892m.Storm

[Justin Toposim 16]

HI,A meter is a meter, a degree a degree when you're working with unprojected data,-------Justinhttp://www.fsgenesis.netHigh Quality Scenery for FS200x

[Guest Stormshadow]

I noted that LOD11 cells are trapezoidal in shape with the horizontal sides parallel and of differing lengths while the sides are inclined and of the same length.I'm using degree to distance calculators to find out what the lengths are.Storm

[Justin Toposim 16]

HI StormThey're perfectly rectangular if you if you plot them unprojected. If you plot them in any of the various projections, you'll get all kinds of irregular shapes, depending on the projection. But if you use plain old latitude/longitude, you get perfect rectangles.MSFS requires unprojected source files in WGS84 datum. If you're working with projected source data, you'll have to unproject (convert them to lat/long) them before processing for MSFS.Hope this helpsJustinhttp://www.fsgenesis.net-------Justinhttp://www.fsgenesis.netHigh Quality Scenery for FS200x

[Guest]

Remember folks the earth still is a model like any other and like all3D meshes uses projections for mapping The math in the program willtake WGS48 formatted data and works out the projection based on the LOD. Thanks Justin for pointing out that the raw info must unprojected (planar) so that the textures will display correctly in the sim sice the earth is in fact a big ball(almost!) Dan

[Guest Stormshadow]

Thanks ppl for the help, have to ask you thought to explain the jargon...things like wgs48.Anyway, what I'm interested in is the actual dimensions of say an LOD11 cell. If you say the the cells are perfectly rectangular, then all cells should be of the same size - then what size is this? and why is it someone mentioend that the cells shrink in the vicinity of the poles?If only someone could provide me with answers to:1. Are cells (say LOD11) of equal size and shape and,2. Simple way to calculate the width and lengths in m's of the cells(I tried using te degree boundaries and came up with the trapezoidal shape I mentioned before).Storm

[arno 1]

In degrees all cells have the same size as noted above, but in meters this means that there is a difference (because the earth is not flat). So then it is correct that you get a trapizium like thing as you mentioned.

[Guest Stormshadow]

Cheers Arno,Ok so I'll work assuming that each cell is rectangular and all cells are of same size. I'll retrieve the size and orientation of the cells using the runways of an airport as guidlines. Should be suitable I guess.Storm

[Justin Toposim 16]

HI Storm,You have downloaded and read the Terrain SDKs, right? Look at the Advanced Topics, Using the Level of Detail (LOD) Directive. There you will find a table with the values for all the LODs.From that table, an LOD=11 cell is19.1mWith a quadrant size of0.043945313 degrees latitude0.05859375 degrees longitude-------Justinhttp://www.fsgenesis.netHigh Quality Scenery for FS200x