Tacview Technical Reference - Terrain
NOTICE: The following documentation is based on Tacview 1.0.
Some of the features shown below such as ETOPO2 base map may not be available in older versions.
World terrain overview
Unlike many flight simulators, Tacview does not try to project a spherical terrain on a flat surface.
Instead, it uses a true spherical earth.
Like Google Earth, Tacview is able to display the earth in its whole like it is in real life.
- Spherical Earth
That way of managing and displaying earth offers the following advantages:
- It's possible to represent the whole earth
- It's easy to add new detailed areas
- Distances calculations are accurate
- No hack is required to display a flight which span across long distances
- Sun position is accurate
However, this way of doing things has some limitations:
- Converting flight simulations flat terrains to spherical terrain is not an easy task
- When flight recording data come from a flat world, distances calculations may not be so accurate because of latitude/longitude distortions
- Because of display optimizations, Tacview is not yet able to properly display terrain close to north and south poles
Terrains used by Tacview
- Terrain Options
Tacview uses three kinds of terrains:
- National Geophysical Data Center ETOPO2 v2g worldwide base map (about 2.5 km resolution)
- Shuttle Radar Topography Mission SRTM3 v2 detailed terrain (about 75 m resolution)
- Terrains exported from several flight simulators and converted into SRTM3 data (Flaming Cliffs, Black Shark, ...)
Below, the first screenshot shows you the ETOPO2 worldwide map displayed in Tacview.
Thanks to several optimizations this worldwide base map takes only 20 MB of memory.
As you can see, it is a pretty good approximation of the earth surface.
The second screenshot shows the same sector based on SRTM3 data (about 75 m resolution).
This is a really high definition map.
Obviously, since SRTM3 terrain represent about 10 GB of compressed data, Tacview includes only the main areas covered by our favorite flight simulators.
The last screenshot shows Flaming Cliffs map exported and converted into SRTM3 format.
In average it is less accurate than SRTM3 terrain. However, since Flaming Cliffs terrain differ from the reality,
it is more appropriate to display its map while reviewing flight recordings from Flaming Cliffs and Black Shark.
When no other map is available Tacview display the ETOPO2 worldwide base map.
Otherwise it displays SRTM3 terrain or flight simulators terrains depending of their availability and user preferences.
At anytime, the user can switch between terrains thanks the option [Settings|Terrain].
Adding or upgrading terrains
The following tutorial explains how to add new terrains to Tacview.
This works with any version of Tacview.
Note that upgrading existing terrain works the same way:
You just have to add your terrain and Tacview will use them instead of those provided by default.
In this tutorial, we are going to add the high definition map of Corsica into Tacview.
First, we must check boundaries of the Corsica terrain.
Since SRTM3 sectors are 1 by 1 degree each, we have to round boundaries to 1 degree.
According to Google Earth, Corsica boundaries are: from N41° E8° to N43° E9°.
- Corsica Boundaries
Then we have to download corresponding SRTM3 sectors from the NASA server.
Those data are free for use by anyone for any purpose!
So let's download our 3x2=6 sectors:
Then we have to unpack those data and put them under the proper folder.
There are two types of SRTM3 terrain which can be customized by the user:
- SRTM3 real-life terrain: %TacviewFolder%\Data\Terrain\SRTM3\
- Custom or flight Simulators terrains: %TacviewFolder%\Data\Terrain\xxxxxx\ (use any sub-folder name you want)
Since our data is from real life, we are going to put it under the SRTM3 folder.
We just have to create the proper sub folders where Tacview is installed and put our unpacked data into it.
That's it! We can now see in Tacview our brand new high resolution Corsica terrain! (See the screenshots bellow)
Fixing SRTM3 terrain holes
However, we can notice holes in our map.
Because of clouds, atmospheric perturbations and trees, the shuttle radar was not able to pick all details.
This is why we have missing data, especially in mountains.
Jonathan de Ferranti fixed data
Here how we are going to fix that:
First, we should have a look at Jonathan de Ferranti web site.
Jonathan has already cleaned many SRTM3 sectors.
Since he used other real-life data to fix those holes, if we can find Corsica Mountains on his web site, we are going to have pretty accurate SRTM3 data.
Here we are: Let's download his Corsica n42e008 sector!
Unpack it and replace our original file by this one.
As you can see this is a huge improvement over original defective data.
John Childs's Blackart
But we still have many tiny holes remaining almost anywhere else!
Now we are going to use a program to fix those holes thanks to mathematical algorithms.
Obviously this is not going to be as accurate as Jonathan work but that will do the job pretty well, especially with our tiny holes.
- Blackart
So, let's go to John Childs's web site to download his (in)famous Blackart.
Blackart is an 'interesting' program: It is painful to use and it crashes all the time... However it is really good at fixing SRTM3 data. As you are going to see, it gives really great results:
- Launch Blackart
- Select [File|Batch Mode Interpolate|SRTM to SRTM]
- Add our 6 SRTM3 sectors to the list
- Select Continue
- Set LSQR Iterations to 100
- Set Laplacian Iterations to 1000
- Set Scale Factor to 1 (because the decimal separator is usually not properly handled)
- Click on [Submit], accept the default -32000 value for null data then [Submit]
- Select [Run|Run Blackart]
Since we selected high quality settings, sectors cleanup will take a lot of time (usually about 1 minute per sector on a 2008 computer). We have to wait until Blackart has completed his work or until he has crashed. Be patient and don't worry.
Original files are not going to be modified, Blackart create new files suffixed hgx.
So you just have to restart the process from where he has crashed.
After this painful (but almost automatic) process we should have our 6 cleaned SRTM3 sectors ready for a new try! So, let's delete (or backup) our original hgt files and rename *.hgx files from Backart to *.hgt.
That's it! We can now launch Tacview and see our new clean high resolution landscape!
The following screenshots show from left to right:
- ETOPO2 Corsica (default worldwide base map)
- Raw SRTM3v2 Corsica for the NASA
- Major holes fixed by Jonathan de Ferranti SRTM3 data
- Final Corsica: Remaining holes has been fixed thanks to Blackart
How can I add my favorite flight simulator terrain into Tacview?
- Falcon 4 Projection
In overall the process is the same as for adding SRTM3 terrain data.
Except that instead of taking data from the NASA, you will have to export and convert it from your flight simulator:
- Extract your flight simulator data
- Convert it to SRTM3 data
- Copy the converted data into %TacviewFolder%\Data\Terrain\xxxxxx\ (use any sub-folder name you want)
The following folders are natively supported by Tacview (however you can use any other name your want):
- \Data\Terrain\SRTM3\ (for real life terrain)
- \Data\Terrain\DCS\ (for Flaming Cliffs and Black Shark)
- \Data\Terrain\DF\ (for Digital Fighters)
- \Data\Terrain\F4\ (for Falcon 4.0)
- \Data\Terrain\OF\ (for Open Falcon)
- \Data\Terrain\AF\ (for Falcon 4.0: Allied Force)
- \Data\Terrain\EECH\ (for EECH)
Depending of the simulator this is a pretty difficult task because of the following points:
- You need to have access to your simulator data in any way (can be thanks to some documentation or thanks to an integrated script language)
- You need to find a way to properly convert flat terrain coordinates into spherical coordinates (longitude/latitude/elevation)
Unfortunately I cannot help you in that task because every simulator is unique. However, here some documentation which may help you:
Do not hesitate to contact me if you need more information or you have any requests.
