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Old 08-31-2019, 04:05 PM   #16
cristiapi
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Quote:
Originally Posted by BrianJ View Post
 I can try and use that first height map, but I'm not sure what the resolution is. It looks like it is a cylindrical projection already.
1:2 greyscale heatmap: http://cristianopi.altervista.org/Bennu-hm.html (I posted the html so you can see the numbers).
1 pixel is 1 degree in both directions (the projection is surely equirectangular; if you really need cylindrical, I can try something else).

Left edge: longitude = -180, bottom edge: latitude= -90. There are 360 * 180 = 64800 points.
To clarify: if you consider the upper-right pixel, it represents the longitudes from 179 to 179.99999... and latitudes from 89 to 89.99999... but the elevation value is given for exactly 179, 89.

Quote:
I just had a quick look at that heightmap in Photoshop - doesn't look good.
Edge pixels are blurred. Looks like there are discontinuities between rows of pixels.
Not in 1:2 proportion so will need to stretch vertically.
Is the new greyscale heatmap better?
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Old 08-31-2019, 04:56 PM   #17
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Quote:
Originally Posted by cristiapi View Post
 1:2 greyscale heatmap: http://cristianopi.altervista.org/Bennu-hm.html (I posted the html so you can see the numbers).
1 pixel is 1 degree in both directions (the projection is surely equirectangular; if you really need cylindrical, I can try something else).

Left edge: longitude = -180, bottom edge: latitude= -90. There are 360 * 180 = 64800 points.
To clarify: if you consider the upper-right pixel, it represents the longitudes from 179 to 179.99999... and latitudes from 89 to 89.99999... but the elevation value is given for exactly 179, 89.



Is the new greyscale heatmap better?
Yes, that looks much more hopeful. Can you upload as a .bmp or .png?
Otherwise I can take a screenshot and crop it.
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Old 08-31-2019, 05:05 PM   #18
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I attached a 360 x 180 and a zipped 1440 x 720 .bmp's.
Attached Images
File Type: bmp bennu.bmp (64.3 KB, 3 views)
Attached Files
File Type: zip bennu_1440-720.zip (197.5 KB, 3 views)

Last edited by cristiapi; 08-31-2019 at 05:18 PM.
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Old 08-31-2019, 07:29 PM   #19
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Perfect!
I'll give it a try and see what we get.
Will get back to you soon.
Cheers,
BrianJ
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Old 08-31-2019, 10:12 PM   #20
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Ok, looking quite good, I think. A bit of pinching at the poles. Also, I had to shift the surface textures 180deg to match the elevation.I'll try and do an update for OSIRIS-REx on OH in the next day or so.


Wikipedia Image/Orbiter2016

Click image for larger version

Name:	bennu_comp.jpg
Views:	12
Size:	250.5 KB
ID:	16785
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Old 08-31-2019, 10:24 PM   #21
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Wonderful!
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Old 08-31-2019, 10:49 PM   #22
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No idea on how much work is needed, so I can only ask.
It would be useful to also have the best fit ellipsoid for the Bennu model; no texture, only a triaxial ellipsoid (I attached the .bmp). I'd be very grateful if you'd also create this model, but if you don't have time, just ignore this post.
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File Type: zip bennu-ellipsoid.zip (42.1 KB, 2 views)
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Old 09-01-2019, 12:58 PM   #23
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Hi,
unfortunately I can't access OrbitHangar to either update or upload add-ons, so temporarily you can download an updated version of OSIRIS-REx (v.190901) from my GoogleDrive here:
https://drive.google.com/open?id=1z4...d6-qeXjq9bkurx

It includes the new Bennu elevation and surface tiles, and .cfg file.
If you install over an older version - you must DELETE your old /Textures/Bennu folder first.

I'll make a start on your triaxial ellipsoid next :-)

Cheers,
Brian
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Old 09-01-2019, 03:31 PM   #24
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Visually stunning! But if you enable the "Visual helpers", the Planetarium mode -> Target Equator line doesn't pass over the equator. Also, if you use Obliquity = 177.6 (a reasonably accurate value), the spin axis seems to be about 100 deg (the ecliptic blue line is almost vertical instead of horizontal).

I don't want to disturb you further; is there a procedure you can recommend to create the elevation data for Orbiter?
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Old 09-01-2019, 04:33 PM   #25
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Quote:
Originally Posted by cristiapi View Post
 But if you enable the "Visual helpers", the Planetarium mode -> Target Equator line doesn't pass over the equator.
Hi,
looks ok to me. Checked by tracking equatorial feature.
Click image for larger version

Name:	bennu_equ_check.jpg
Views:	10
Size:	413.5 KB
ID:	16787

Quote:
Originally Posted by cristiapi View Post
 if you use Obliquity = 177.6 (a reasonably accurate value), the spin axis seems to be about 100 deg (the ecliptic blue line is almost vertical instead of horizontal).
For the .cfg files, units are radians not degrees.

Quote:
Originally Posted by cristiapi View Post
 is there a procedure you can recommend to create the elevation data for Orbiter?
Here's my rather clunky manually work-intensive procedure:
https://orbithangar.com/showthread.p...7&postcount=24
or try googling for "orbiter forum elevation". Also, have a look in Orbiter Doc/PlanetTextures.pdf.



Cheers,
Brian
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Old 09-01-2019, 06:15 PM   #26
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Quote:
Originally Posted by BrianJ View Post
 looks ok to me. Checked by tracking equatorial feature.
I'm probably misinterpreting the meaning of the lines, but I think there's something strange. I'll do some testing...

Quote:
Originally Posted by BrianJ View Post
 For the .cfg files, units are radians not degrees.
Ooops! You're right.


Quote:
Originally Posted by BrianJ View Post
 Here's my rather clunky manually work-intensive procedure:
https://orbithangar.com/showthread.p...7&postcount=24
or try googling for "orbiter forum elevation". Also, have a look in Orbiter Doc/PlanetTextures.pdf.
Thank you. I already read PlanetTextures.pdf, it's the reason I asked here. :-)
I'll try the procedure for the triaxial model. Don't waste your time. :-)

Ciao e grazie
Cristiano

Last edited by cristiapi; 09-01-2019 at 06:17 PM.
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Old 09-01-2019, 06:57 PM   #27
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Hi,
no worries :-) Thanks for uploading the altimetry data image.

The visual helper "Target Equator" green line is a projection of the target planet's equator onto the Celestial sphere, as far as I know.

For a more accurate orientation of Bennu, you may want to figure out the axis LAN parameter in the .cfg file (currently set to LAN = 0 ).
The Wikipedia entry for Bennu gives RightAscension and Declination of the N.Pole, so it can be calculated from that. (I might have a go at some point).

Also, the rotation offset needs to be set (currently set to SidRotOffset = 0).
You might be able to do that if you have an image of Bennu with a time stamp from the spacecraft.

Do let me know if you figure out those parameters!
Cheers,
Brian
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Old 09-02-2019, 09:46 AM   #28
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Quote:
Originally Posted by BrianJ View Post
 The visual helper "Target Equator" green line is a projection of the target planet's equator onto the Celestial sphere, as far as I know.
The first strange thing is that that line is purple in my installation (Orbiter 2016).
Beside that, I attached one image of Bennu and one of the Earth (for comparison).

I used the global frame (F2) and I oriented the camera to see the retrograde Bennu rotation. To see the line passing over the center of Bennu, I needed to look from about 45 deg nord.

Now I changed to a well known celestial body without changing the camera orientation. We see the south pole up (which is correct) and we see the line passing exactly over the equator when we look the Earth from over the equator, which is also correct, but that doesn't happen with Bennu (I hope that my "English" is clear enough).

I'm not totally sure that it's a problem, but it seems strange to me.

Quote:
For a more accurate orientation of Bennu, you may want to figure out the axis LAN parameter in the .cfg file (currently set to LAN = 0 ).
The Wikipedia entry for Bennu gives RightAscension and Declination of the N.Pole, so it can be calculated from that. (I might have a go at some point).

Also, the rotation offset needs to be set (currently set to SidRotOffset = 0).
You might be able to do that if you have an image of Bennu with a time stamp from the spacecraft.
Since I use SPICE to do all the calculation, I can calculate and verify anything, but the problem is to understand the exact meaning of those parameters in Orbiter.

What I'm trying to do is to use Orbiter as a 3D visualization tool. All the bodies are moved with the SPICE library (I'm currently using Orbiter 2010) and I orient ORX using the NAIF's data file (which include also the instrument FOV). I'm currently intersted in the preliminary survey phase. In other words, I need a perfect setup! :-)

Quote:
Do let me know if you figure out those parameters!
You can bet! :-)
Attached Thumbnails
bennu-equ.jpg   earth-equ.jpg  

Last edited by cristiapi; 09-02-2019 at 09:53 AM.
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Old 09-02-2019, 11:18 PM   #29
BrianJ
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Hi,
I have a hunch you're using the D3D9 graphics client for Orbiter, yes?
For some reason the "Target Equator" display in D3D9 is a purple line and always shows along the Celestial sphere equator (whatever the target is). Try using the default Orbiter2016 graphics - the line is green and looks like it is in the correct place relative to Bennu (to me anyway!).

If you're using SPICE to set the orbit and orientation, I guess you won't need to bother with those parameters in the .cfg file?


FYI, from those red/blue height maps, I estimated the maximum elevation to be 287m, and minimum 215m, and processed the image accordingly. This may not be accurate enough for you. Do you have more accurate max./min. elevation values?

Otherwise I have to rely on moving the cursor around on the height map image and hoping I can find the max/min points. I can already see I'm out by at least 2m on the overall elevation range.

Not much work to re-do those values and run the ele2png.exe
I'll have another go with more accurate max/min values.

Cheers,
Brian
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Old 09-03-2019, 03:31 PM   #30
cristiapi
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Quote:
Originally Posted by BrianJ View Post
 Hi,
I have a hunch you're using the D3D9 graphics client for Orbiter, yes?
For some reason the "Target Equator" display in D3D9 is a purple line and always shows along the Celestial sphere equator (whatever the target is). Try using the default Orbiter2016 graphics - the line is green and looks like it is in the correct place relative to Bennu (to me anyway!).
You're right! With the default graphics it looks good.

Quote:
If you're using SPICE to set the orbit and orientation, I guess you won't need to bother with those parameters in the .cfg file?
With SPICE I obtain the "exact" location of the bodies, but if I also want a correct Bennu prime meridian location, I also need to bother with those parameters (I remember the same for Pluto/Charon synchronism).

Quote:
FYI, from those red/blue height maps, I estimated the maximum elevation to be 287m, and minimum 215m, and processed the image accordingly. This may not be accurate enough for you. Do you have more accurate max./min. elevation values?
The values are 214.55 m and 289.351 m, but if we consider the .bmp image, those 8-bit converted altitudes become 214.404 and 289.205.

Quote:
Not much work to re-do those values and run the ele2png.exe
I'll have another go with more accurate max/min values.
Thanks a lot

---------- Post added at 16:31 ---------- Previous post was at 09:46 ----------

Quote:
Originally Posted by BrianJ View Post
 Here's my rather clunky manually work-intensive procedure:
https://orbithangar.com/showthread.p...7&postcount=24
At step 2 I read that you scale an image to several resolution; isn't it better to have all the necessary .bmp without having to scale them?
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