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SRTM 1 Arc-Second and FreeMeshX

R

Rafal Wator

Messages
115
Country
poland
Hello.

FreeMeshX is propably best free mesh avaliable. I`ve downloaded from USGS 1 Arc-Second data for region I need for my project. I assume FMX use same data. I don`t now much about the process to make own mesh. I try to make it myself to make use just small region not whole Europe. What I did:
First download data in GEOTIFF format and put in Global Mapper. I followed tutorial on YT :

When I finished i resampled with that settings :

[Source]
Type= GeoTIFF
SourceDir = "."
SourceFile = "Tatra_38m.tif"
Layer= elevation
NullCellValue=-32767
PixelIsPoint=1

[Destination]
DestDir ="."
DestBaseFileName = "Tatra_38m"
DestFileType = BGL
BaseValue = 1000
FractionBits = 2
LOD =auto

In tmfviewer I compared my bgl file and this from FreeMeshX and noticed that both are at LOD10 but this one from FreeMeshX is much more accurate and wondering why. Is it something in resample settings or something is missed in tutorial and I need to process it in Global Mapper to be as accurate as FreeMeshX one. Below 2 pictures that show the difference. It`s the same LOD10.
1.JPG
2.JPG
 
And how does the elevation data look when you view it in GlobalMapper? Do you see more detail in that case?
 
Yes I think it`s more detail . In Sim I can`t see difference between default mesh that is 78m or 90m but when i load FreeMeshX i see it`s much better and more accurate comparing to real satellite imagery.

3.JPG
 
Hi Rafal:

Did you load in FS, your BGL output by FS SDK Resample from the above SRTM-30 Meter source data and the above INF file ? :scratchch

BTW: You may wish to also try Global Mapper's built-in online data download for the ASTER GDEM V2 30 Meter elevation data. :idea:


PS: Be aware that in Global Mapper`s 3D view, when the "Emphasize Height" Icon Bar Button is clicked more than 3 to 5 times above a 'zeroed' minimum base level, it adds artificial detail to only that 3D view, and not to the actual gridded elevation data that will be exported to a GeoTIFF. ;)


FYI: Detailed steps for working in Global Mapper with downloaded aerial imagery and elevation data that is to be exported in a GeoTIFF file format compatible with FS / P3D SDK Resample ...are here:

http://www.fsdeveloper.com/forum/threads/help-with-global-mapper-and-scenery-use.439100/

http://www.fsdeveloper.com/forum/threads/about-geotiff-resmaple.430118/


Hope this helps ! :)

GaryGB
 
Last edited:
Thanks GaryGB. To answer previous question I loaded elevation bgl file I created and it`s better then default for sure but little worse then FMX but in FMX was an error with long zero alt gasp but in my mesh it`s fine so I don`t know where does this difference come from maybe it`s Aster, but will read above thread for sure. Here are the pictures 1 is def 2 is my work 3 is FreeMeshX
 
Hi Rafal:

Looking very good so far ! :cool:

I'll be interested to see how a screenshot from your saved flight looks using the Global Mapper built-in online data download for ASTER GDEM V2 30 Meter elevation data. :scratchch

[EDITED]

I'll also be interested to see a comparison screenshot from your saved flight using the Tatra SRTM-1 Arc Second (30 Meter) elevation data from Jonathan de Ferranti's web page ...linked by Holger below:

http://viewfinderpanoramas.org/dem1.html


FYI: When the Tatra area rectangles are located / clicked via the above cited dem1 map view:

www.viewfinderpanoramas.org/Coverage%20map%20viewfinderpanoramas_org1.htm

...this linked file can be downloaded: :)

http://viewfinderpanoramas.org/dem1/TATRA.zip

[END_EDIT]


GaryGB
 
Last edited:
Hi there,

clearly not the same source data and ASTER DEM would probably be worse (best to stay away from it unless your project is in a dry area where ASTER's sensors exhibit less artifacts).

Many mesh developers still prefer to use Jonathan de Ferranti's file sets over the "basic" SRTM source: http://www.viewfinderpanoramas.org/dem3.html

In fact, looking at his 1-arcsec (~30-m resolution) page it appears that he's made files for the Tatra Mountains, perhaps that's what the FreeMesh dev was using as well: http://www.viewfinderpanoramas.org/Coverage map viewfinderpanoramas_org1.htm

Cheers, Holger
 
Thanks for reply I saw HGT files in GlobalMapper and it looks better like FreeMeshX but now don`t know how to convert to tif file. When I export to tif file resample doesn`t start so I can`t compare it without knowledge how to cope with hgt format. I will try to google that issue I suppose it`s raw format. Besides is it open source of data I mean can I use it for distribution if i put elevation files in my Tatry project... ?
 
Hi Rafal,

not sure why the deFerranti files wouldn't work for you. Those .hgt source files are already in Geographic projection with WGS84 datum so they just need to be exported in their current projection as 32-bit elevation GeoTIFF.

To generate the .inf file I load the tif into GlobalMapper and then copy&paste the metadata into an existing template like the example below. Technically, one doesn't need to provide all the projection parameters as they already exist in the tif's header data. It's just personal preference of mine to also copy them into the .inf file for quick visual reference or in case I want to create subsets.

[Source]
Type = Geotiff
Layer = Elevation
SourceDir = "."
SourceFile = "mesh_Tatra_Mountains_deFerranti_30m.tif"
ulxMap = 19.0000000000
ulyMap = 50.0000000000
nCols = 7201
nRows = 3601
xDim = 0.0002777777777777
yDim = 0.0002777777777777


[Destination]
DestDir = "."
DestBaseFileName = "mesh_Tatra_Mountains_deFerranti_30m_LOD4-11"
DestFileType = BGL
UseSourceDimensions = 1
NorthLat = 50.0000000000
SouthLat = 49.0000000000
WestLong = 19.0000000000
EastLong = 21.0000000000
CompressionQuality = 97
LOD = 4,11
FractionBits = 2
Click to expand...

Cheers, Holger
 
Thanks a lot Holger I tried and it works now :) One more thing not exactly related to this thread but I couldn`t find answer to my question on FsDeveloper or I haven`t been looking patiently. Regardless of settings how about loading time of photoscenry. I have LOD 16 and wondering what resample ini file settings would be the best for faster photoscenery loading time. Below 200kts photoscenery loads fast enough but at high speed it turns blurry. Does compression quality affect loading time ? For example smaller bgl file at CQ 80 will load faster or at 100. I can`t use LOD 15 that would increase texture load propably. I resample at auto but there is option like 15,16 or auto,16. I tried myself but can`t see any difference.
 
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