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Mapping Venus

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Mapping Venus

Postby planethopper9 » Mon Jun 08, 2020 7:13 pm

I've been tasked to create a Venutian flight environment and I'm using FlightGear as the flight simulator.

Using the data from the Magellan spacecraft that mapped Venus back in the '90s I'm trying to convert the SAR (Synthetic Aperture Radar) data at https://pds-imaging.jpl.nasa.gov/data/m ... 1/f05s335/ from *.img files to the next FG acceptable format.

I know the end result is *.btg.gz and *.stg files in the Terrain folder. I've read the entries here concerning TerraGear, I'm just having problems with the .img conversion process.

How are the SAR files that are in .img format translated to DEM format that will eventually become .hgt files?

Thanks.
planethopper9
 
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Re: Mapping Venus

Postby vnts » Tue Jun 09, 2020 10:17 pm

planethopper9 wrote in Mon Jun 08, 2020 7:13 pm:I'm trying to convert the SAR (Synthetic Aperture Radar) data at https://pds-imaging.jpl.nasa.gov/data/m ... 1/f05s335/ from *.img files to the next FG acceptable format.

Are you sure this is the exact data product you are looking for? From the site: https://pds-geosciences.wustl.edu/missions/magellan/

That SAR data is a measure of the strength of the backscatter echo (reflectance, average roughness, complex geometry/wavelength effects, 'shading' based on slope, and other things that affect radar), at the specific frequencies of the radar pulse, that is returned to the antenna corresponding to each image element. In an image format this will only be 8 bit resolution - needing to be encoded logarithmically.

What terragear wants is a digital elevation model - topography. The corresponding measurements are altimetery data (from things like time of flight), and any available data derived from multiple sources like stereoscopic observations etc. This data should be 16+ bits per point.

Terragear creates a coarse mesh (google image). After that, Flightgear can additionally paint finer details using procedural texturing - this process can use some indirect influence from SAR backscatter at microwave frequencies, and any other useful data products relating to surface characteristics like roughness or hints at materials. If you need to create a visual representation of Venus, i.e. at optical frequencies, influence from SAR will have to be pretty indirect to guess surface materials.
planethopper9 wrote in Mon Jun 08, 2020 7:13 pm:I'm just having problems with the .img conversion process.
..
How are the SAR files that are in .img format translated to DEM format that will eventually become .hgt files?

The DEM should be created first from a suitable topography data set. You would likely need to unencode to geocentric coordinates according to the formula NASA gives first, and possibly change to format/resolutions of file formats used by Terragear.

Google appears? [1] to suggest .hgt files have a hardcoded grid sizes. If this is true, to avoid having to do interpolation/upsampling it may be worth checking if there's another format that accepts custom grid size, or if Terragear can be told to work with custom/varying(?) grid sizes.

There is also a Spaceflight forum (link) you can ask there too in case devs who are afk might miss this thread - and maybe the devel mailing list if you don't get a response. (It may help to say what you are trying to use the Venus reconstruction for, and also if it's related to university work you are being assessed on.)

Unlike Mars, Venus does have a dense atmosphere that can generate dynamic head needed for flight very easily :mrgreen: - the surface is almost like being under water in a sea of super-hot liquid CO2 :twisted: (although it does get more hospitable/Earth-like high up AIUI).

Kind regards
vnts
 
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