Discussion Mars Express/HRSC

martins

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The other day I attended the i-Mars Final Dissemination Event here at UCL (it's nice to find that your Uni shares interest in your hobby ;) )

i-Mars is (or was) a project to use high-resolution imagery (mainly the HRSC datasef generated by Mars Express, but also locally CTX and HiRISE) to create co-registered 3D datasets including elevation and orthoimages. They specialise mainly on finding change (new impacts, moving dunes, dust devil tracks, polar ice falls, etc.), but also showed a few cool 3D movies of terrain flyovers.

This got me to look into the HRSC data to use for Orbiter, to replace the current MOC/MOLA data. Unfortunately HRSC currently has got fairly patchy coverage, and they don't seem to provide high-level data products so far, so I'll need to stitch the mosaics together myself. But certain scenic areas like Valles Marineris and Olympus Mons seem to be well-covered, so I'll try a local high-res treatment of Valles Marineris to see if this is feasible.
 

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I haven't checked recently myself either, but is there any chance that Pavonis Mons is included in the Valles Marineris and Olympus Mons datasets?
 

martins

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I haven't checked recently myself either, but is there any chance that Pavonis Mons is included in the Valles Marineris and Olympus Mons datasets?

The front page of the i-Mars site contains the current level-4 DTM coverage (actually from 2015, according to the caption). According to that, Pavonis Mons is not covered. In fact I may have been wrong about Olympus Mons as well.

Level-3 coverage is more extensive (75% of the surface according to another quote), but I think level-3 doesn't contain the stereo DTM data. I don't know if only a subset of the level-3 data is suitable for level-4 generation, or if they are simply still in the processing pipeline.

I am currently generating a global DTM mosaic from all the level-4 data I can find (up to orbit 6500) to see what is available. Might take me a while to download and process.

Edit: Level-5 coverage is even sparser. Level-5 contains the co-registered mosaics. (hopefully including seam removal). Currently there appears to be only a single area ("MC11E", identified on the i-Mars image) available at level 5. This area was of interest since it contains a number of landing sites.
 

martins

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Just a quick update on this. It's taking a bit longer than expected (and I am feeling bad for neglecting potentially more pressing issues for this, but hey, it's my hobby ;) ):

I have pretty much completed the HRSC elevation layer (using the current MOLA data to fill the gaps). This is looking quite reasonable, but may need more work. I am currently averaging the data from overlapping HRSC fragments, but it would be better to establish a quality ranking of the fragments and add them to the mosaic in order of quality (worst to best). Mars Express has quite an elliptic orbit, so the camera distance varies considerably. And since the data are generated from stereo images rather than radar distance measurements, image quality (lighting conditions, local weather) also affect the elevation data quality. I am in contact with a researcher at FU Berlin who is working on the HRSC data, and I got a quality ranking list for some parts of the surface which I will try for this.

The surface texturing will take more work. For a start, the amount of data is huge (12.5 m resolution for the panchromatic nadir images - my 2TB drive dedicated to Mars data is slowly filling up with the HRSC data).

The first processing step is a brightness correction against a global albedo reference. I am using my MOC mosaic for that: The global MOC mosaic is mapped into a low-resolution bilinear basis expansion. Each of the HRSC fragments is mapped into the same basis, the basis coefficients are shifted to fit the reference, and then used to adjust the low spatial frequencies of the full resolution HRSC fragment. In other words, at frequencies of the basis expansion and lower, the surface will look like the MOC reference, while higher frequencies will make use of the HRSC high resolution data.

Next, the fragments are feathered and added on top of the MOC background.

Adding HRSC colour channels is yet more work. The colour channels are lower resolution (50m) than the panchromatic channel, so I will need to employ some pansharpening mechanism. I am trying different colourspace conversions (HSV, HSI, HSL, LAB) to see which extracts the closest match to the nadir channel.

The other problem is that there is no real global colour reference to match the fragments to. According to a paper, the FUB guys are simply matching against a constant "Mars" colour at low frequency, but maybe I can do a little better and use the MDIM/Viking composite as a reference. Problem is, I am not too happy with the albedo on this image, so I might try to do another colourspace conversion and swap the intensity channel against MOC. I might need to do the entire mosaicking in HSI space anyway, because some HRSC fragments have a nadir channel but no colour channels.

To top it all, the original MOC data was mapped into an areographic reference frame, while MOLA and HRSC are using areocentric coordinates. For the current Orbiter Mars data, I mapped MOLA to areographic, but now it makes more sense to map everything to areocentric (and it better matches Orbiter's rendering geometry anyway). Also, I am now using elevation data referenced against the reference sphere instead of the geoid, so the oblate ellipsoid shape of Mars will be correctly represented.

TL:DR: I'm still crunching away at making Orbiter better :cheers:
 

martins

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Excellent Textures martins! Any plans for Mercury or Venus?
 

martins

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Excellent Textures martins! Any plans for Mercury or Venus?

Don't know - do you have sources for good quality high resolution orthoimages and DTMs?

I always have a slightly bad conscience when spending a lot of time on those textures. My time would probably be better spent on actually working on the Orbiter code. The textures could really be done by anybody with a bit of geoimage processing knowhow and way too much time on their hands.
 

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Don't know - do you have sources for good quality high resolution orthoimages and DTMs?

I always have a slightly bad conscience when spending a lot of time on those textures. My time would probably be better spent on actually working on the Orbiter code. The textures could really be done by anybody with a bit of geoimage processing knowhow and way too much time on their hands.

And some CPU cycles spare... and a Matlab license AFAIR, or did this change?
 

martins

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And some CPU cycles spare... and a Matlab license AFAIR, or did this change?

Well yes, for most of my processing pipeline I'm using Matlab, but that's just a matter of convenience, since I am pretty familiar with it. But since much of the pipeline needs to be rewritten from scratch for each new project anyway, this isn't written in stone. Much of the Matlab code is just invoking external GIS utilities like GDAL, and I suspect GDAL integrates much better with Python than Matlab.

Some of the tools I did do myself (for example an edge-distance function I am using for feathering the image fragments when building mosaics), I did in C++ for performance's sake and then just compiled into a Matlab mex file. Probably compiles just as well into a Python module. You are welcome to it if you want to give it a go. :thumbup:
 

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Well yes, for most of my processing pipeline I'm using Matlab, but that's just a matter of convenience, since I am pretty familiar with it. But since much of the pipeline needs to be rewritten from scratch for each new project anyway, this isn't written in stone. Much of the Matlab code is just invoking external GIS utilities like GDAL, and I suspect GDAL integrates much better with Python than Matlab.

Some of the tools I did do myself (for example an edge-distance function I am using for feathering the image fragments when building mosaics), I did in C++ for performance's sake and then just compiled into a Matlab mex file. Probably compiles just as well into a Python module. You are welcome to it if you want to give it a go. :thumbup:


Good to know :) Venus would be some stronger problem, since we have only radar altimeter data and would to guess on the geology.

But AFAIR, Venus would be a the best next candidate since we have full Magellan data of it. Mercury is still WIP.

Not sure if I can really give it a go, I still know about nothing about how to do such a project. But it sounds like a solvable problem, for example like OpenFOAM, which is a series of specialized C++ modules based on a common domain model chained together by configuration files to process a simulation. Maybe it would be possible to do the same to have something like a common backend for Orbiters planet texture model and changing front-ends and middleware processing pipelines for different data sources.
 
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Don't know - do you have sources for good quality high resolution orthoimages and DTMs?

This will start you on the right direction, as far a I know:
https://astrogeology.usgs.gov/searc...es/Venus_Magellan_Topography_Global_4641m_v02

I only ask that if you convert the radar "surface" images, you invert the brightness scale. To me it looks perfectly realistic with darker basalt tones. I hate that bright orange look...


On that site, there are other "products" available, like Pluto, just browse that site for Digital Elevation Maps:
https://astrogeology.usgs.gov/searc..._presentation_form&v1=Digital+Elevation+Model
 
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