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Problem after converting mesh.

Rotornut44

Rotornut44

Resource contributor
Messages
673
Country
us-florida
Hello. I'm trying to convert some 3 meter resolution mesh, but I'm encountering a problem. I have included a picture below, showing the .bgl in the Resample program.

WXEEZJU.png


As you can see, it displays a layer of purple surrounding the coverage area, which in the simulator, turns into a deep hole, sometimes miles deep.

YJYUL9Q.png


Does anyone know how to fix this problem? This has happened on many different mesh projects and its kind of a pain. Any help is appreciated.

Thanks,
-CB
 
Hi,

What kind of elevation value do you see for the purple areas? I guess the no data value of your data has not be set correctly in the INF file.
 
arno said:
Hi,

What kind of elevation value do you see for the purple areas? I guess the no data value of your data has not be set correctly in the INF file.
Click to expand...

Hello. I'm not sure what the exact elevation value is. I know its in the negatives, but I'm not sure of the exact number. Also, I did use the .inf file example provided with the FSX SDK, so that may have something to do with it. Here is a copy of the format I used.

Code: 
[Source]
Type = MultiSource
NumberOfSources = 6

[Source1]
Type  = GeoTIFF
Layer  = Elevation
SourceDir  ="."
SourceFile  ="Chattanooga3m.Tif"

[Source2]
Type  = GeoTIFF
Layer  = Elevation
SourceDir  ="."
SourceFile  ="counties.Tif"

[Source3]
Type  = GeoTIFF
Layer  = Elevation
SourceDir  ="."
SourceFile  ="Memphis.Tif"

[Source4]
Type  = GeoTIFF
Layer  = Elevation
SourceDir  ="."
SourceFile  ="Nashville.Tif"

[Source5]
Type  = GeoTIFF
Layer  = Elevation
SourceDir  ="."
SourceFile  ="ShelbyCo.Tif"

[Source6]
Type  = GeoTIFF
Layer  = Elevation
SourceDir  ="."
SourceFile  ="smoky.Tif"

[Destination]
DestDir = "."
DestBaseFileName = "3mcoverage"
DestFileType = BGL
LOD = Auto

-CB
 
In the TmfViewer you can hover over the area and the status bar will show the actual value. It might be the NoData value is -32767 for example, so in that case you need to specify that in the Inf file as well.
 
arno said:
In the TmfViewer you can hover over the area and the status bar will show the actual value. It might be the NoData value is -32767 for example, so in that case you need to specify that in the Inf file as well.
Click to expand...

Ok. When I hover over it, it shows it as -32767 exactly. So, how does this NoData entry go into the .inf?
 
Ah. Never mind, I got it figured out. Just recompiled and it seems to have fixed the problem. Now to load it in the sim and find out for sure.

Thanks for your help!
-CB
 
Yeah the issue there would be using a base elevation figure. Basically what happens is there's a certain number of elevation bits that can exist for a BGL (they're basically 16 bit BGL files), so you can only go up to a certain elevation before it gets lopped off. So you set your base elevation to compensate, sorry it's Christmas day and that may sound as clear as mud but I can explain more clearly when I get a sample together for everyone ;)
 
Hi christopherbritton,
Can you tell me how did you get the terrain mesh because i'm looking for it a long time ago but i didn't find it. So, please tell me please !
 
In the destination section of your data you will want to add a basevalue= parameter:

Code: 
[Source] 
Type                = GeoTIFF 
Layer               = Elevation 
SourceDir           = "SourceData" 
SourceFile          = "DeathValleyTif.Tif" 

[Destination] 
DestDir             = "Output" 
DestBaseFileName    = "DeathValley_Elevations" 
DestFileType        = BGL 
LOD                 = Auto 
[COLOR="Red"]basevalue=_______[/COLOR]

The underscored part is where you place a minimum value.

Long story short say you have a mountain peak at 10,000m and the top of the mountain higher than 7,000m is getting cut off then you'll need to add a base value. For the tiled area you would need to find the lowest elevation point (say for example it's 3,004 meters for the lowest elevation point and 10,000m for the highest elevation point) in your elevation source file (i.e. BIL, Geotiff etc).

In that case you'll want a base value slightly lower than the lowest elevation point in your source file:

Code: 
[COLOR="Red"]basevalue=3000[/COLOR]

Basically the way resample works is it starts from a negative value depending on the fraction bits you use. e.g.

-32280m to +32280m <- not a real sample indicative only
-16140m to +16140m <- not a real sample indicative only
etc etc etc down to -100 to +100 etc <- not a real sample indicative only

So in the above resample example of the 10,000m mountain getting cut off here's what your basevalue= line does.

output bgl data range before base value = -7000 to +7000 (i.e. the starting point for all data in the generated BGL starts at -7000, which is silly as the lowest point on earth is close to MSL)

output bgl data range after base value = +3000 to +17000 (i.e. the starting point for all data in the generated BGL starts at 3000 giving you a much higher ceiling for you to work with with your mountaintop)

Without a basevalue= inserted, anything that goes over your top data range value ends up getting cut off and creating a massive hole in your data. When you set the base value for your data range, then the tops of your mountains won't get cut off...

I will dig around for my excel spreadsheet for my fraction bit calculator.
 
Last edited:
Dayou said:
Hi christopherbritton,
Can you tell me how did you get the terrain mesh because i'm looking for it a long time ago but i didn't find it. So, please tell me please !
Click to expand...

Hey Dayou,
Sorry for the very late reply, I don't really come around here unless I have a question that needs to be answered.

Anyways, I usually get all of my mesh from the USGS Viewer website. Sadly it only covers the United States and Territories though, so it wont be of much use for projects in other countries.

Link: http://viewer.nationalmap.gov/viewer/
 
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