# Mesh LOD and NW Boundary

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Evening all,I'm still not convinced about the mesh procedure albeit getting the mesh correctly positioned in FS....and the parameter which is I've yet to digest well is the north west coordinate.So in the info file we have to supply a level of detail which in my view determines the distance between sample points. The higher the LOD the higher the resolution. Fine.Why then is the NW coordinate the actual NW coordinate of an LODXX cell/area? Should it not be the NW in FS which represents the NW coordinate of your mesh DEM, or rather the start of the DEM data (top-left most point)? I hope you understand what I'm trying to suggest :)Storm

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See what I cannot yet understand, and I wish some1 could be crystal clear on this, is the difference between LOD as resolution (the distance between sample points if you may), and and LOD cell, or rather when we speak about the "NW coordinate of your LOD boundary" - LOD calculator does that, finds the NW coordinate of say LOD12 - Shouldn't LOD be just a resolution parameter??Another question:If you set LOD = AUTO right,how can you caluclate the NW coordinate of your freakin LOD boundary when you don't even know what the LOD is!!!??Storm

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Phew Steve! You made my head spin!!Cheers for the explanation! Sorry if I bored you out m8, I'm simply one of those lads who prefers understanding 90% of things together with experimenting rather than doing it blindfolded. >> My situation is an exception? In what way am I exceptional :) ?>> Ok Steve, let's take if from here (if I've sickened you out ignore me :)) )The following is taken from the FS2002 SDK[Destination]LOD = AutoDestBaseFileName = "rainier"UseSourceDimensions = 1[source]Type = ElevS16LSBSourceDir = "x:dem"SourceFile = "dem_100m_mtrainier.dat"Lat = 46.99916666667Lon = -121.9466666667NumOfCellsPerLine = 457NumOfLines = 375CellXdimensionDeg = 0.0008333333333333CellYdimensionDeg = 0.0008333333333332ScaleinMeters = 1.0Question: give me a straightforward answer: how did the author get to the Lat and Lon coordinates? Do these represent the NW coordinate of some LOD cell or just author selected values?CellX... and CellY... should be calculated in accordance with the LOD one is using together with the no. of rows and columns of the raw data image, am I correct? If yes, again, if LOD is unknown, how were these values computed?CheersStorm

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Steve, bare with me - no dem data is available for this minute but fabulous Island so I have to go about it manually using grey images.I've abondoned using 1 LOD13 quadrant/area as I never got bgls compiled, anyones guess why. I reverted to LOD11 and I get fairly decent mesh.Basically what I do is create LOD11 sectors - Take a top-down view of one particular LOD11 area or sector, and superimpose terrain contour data onto this using coastlines as guidelines. I get my grey mpa, convert it to .dem using the nice little tool Grises50 (thumbs up to the author), and compile my info file assigning the NW coordinate calculated through LOD Calculator to the NW parametr in the inf file. Thats the process in a nut shell.Am I correct saying that since I'm using LOD11 resolution, I should get my elevation posts at 19m or so from each other? My grey-level maps are highly detailed - using 5m separation - but I still get tent like mesh and I don't think the mesh is being rendered to the resolution I'm stipulating. (I've given aswell on setting the terrain parameter to 20 or 21 as it too gives me many tent like features). I don't get the 5m and at times 10m contour elevations.That's why I re-started my investigation in the info file. I thought I could leave LOD = 11 together with the NW coordinate as they are and simply change the X and Y values, using the separation of an LOD13 rather than LOD11. Didn't work.Storm

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>Steve, bare with me - no dem data is available for this minute but >fabulous Island so I have to go about it manually using grey images.I understand. I have a couple of islands I'd like to model as well and may have to resort to this approach. But I have not tried it yet so bear with me as well.>I've abondoned using 1 LOD13 quadrant/area as I never got bgls compiled,>anyones guess why. I reverted to LOD11 and I get fairly decent mesh.It should work, but the sim can't render that much detail anyway, so 11 is a better choice.It sound like the problem is not the coordinates, if the mesh works and is showing up where you expect it to be.>Am I correct saying that since I'm using LOD11 resolution, I should get>my elevation posts at 19m or so from each other? Yes.>My grey-level maps are highly detailed - using 5m separation - but I still >get tent like mesh and I don't think the mesh is being rendered to the resolution >I'm stipulating. I'm afraid you may be. Resample works with 1m elevation resolution and source data is available in 1m, 1ft and even some at 1cm resolution! While constructing 10m mesh for the almost flat coastal area of New Jersey, I had to deal with adjacent source data quadrants that differed in elevation along the boundary between them. A difference as small as 2m created a small "cliff" extending for miles that was obvious from thousands of feet AGL. On the ground it looked terrible, so I had to spread the transition over a wider area so it was not so obvious. If your elevations are in increments of 5m then you will get very rough terrain, and a higher TMVL value will just emphasize it. I suspect the only way to eliminate the blocky appearance is to use much closer intervals (a lot of work, if you have the information necessary).An alternative is to use a much lower LOD, which will have the reverse effect of using the higher TMVL values. This might be worth trying.This is probably the explanation for the blocky appearance of the photoreal terrain for Spain (ESCENARIO DE LA RIOJA.ZIP), when viewed with higher TMVL values. It looks great with the default value though. You might want to see if you can determine what LOD he used. His readme.txt file does not provide details regarding construction, but:"If you have any question, please tell it to me:Julio Estefan

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Cheers Steve,Err, so basically I have to get hold of contour maps which are at 1m resolution - jeez that's gona be tough. The ones I have at the moment show contours separated by 2.5m but I can't use this as Grises50 supports integer values not real (decimal). That's why I'm using a resolution of 5m which is the next best alternative.By the way I tried using a lower LOD - I kept LOD=11, same NW coordinates, but used the Lad Deg Boun and Lon Deg Boun for LOD's smaller than 11 in the formulas for CellXdimensionDeg and CellYdimensionDeg. I got a bgl but the result is that the whole area is pancake flat at some elevation level.Storm

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