Beginner level projection Options

[adamg]

Hi,

I'm trying to do the mapping just using SPICE for the Junocam images rather than going through ISIS. It might seem like I'm making life difficult for myself but I just wanted to make sure I'm doing the bare minimum amount of processing so it looks as close to a non-spinny-push-frame image as I can. I'm making all the beginner mistakes but I can't seem to figure out what they are so I was hoping someone might give me a hint?

First I want to figure out how far Jupiter is because I want to have anything that didn't hit Jupiter get mapped to a sphere that hits Jupiter. This means any lens effects can get mapped in space near where they originated from which should hopefully make the edges of the planet seem less processed:

[jupiterPos, jupiterLt] = spice.spkpos('JUPITER', et0, 'JUNO_SPACECRAFT', 'NONE', 'JUNO')
jupiterDistance = np.linalg.norm(jupiterPos)

Then I go through all the undistorted Junocam pixel vectors and figure Jupiter intercept points in the IAU_JUPITER frame so now I have a point cloud of all the planet mapped pixels:

[point, trgepc, srfvec, found ] = spice.sincpt(
'Ellipsoid', 'JUPITER', et,
'IAU_JUPITER', 'LT+S', 'JUNO_SPACECRAFT',
'JUNO_JUNOCAM', v)

If it didn't find an intersection then I figure out where that invisible sphere is going to be by extending out the pixel vector by the separation and move that to the IAU_JUPITER frame:

direction = np.array(v)
pos = direction*jupiterDistance/np.linalg.norm(direction)
rotationMatrix = spice.pxform('JUNO_JUNOCAM','IAU_JUPITER',et-jupiterLt)
pos = spice.mxv(rotationMatrix, pos)

It works terribly! I seem to have a timing error in the frame offsets that seems suspiciously close to the light time between Jupiter and Juno and the sphere that catches all the sincpt misses is completely miles off. I've been staring at the code for a while and not figuring my mistake, I was hoping someone might point out where I've gone wrong.

Many thanks


Adam

[adamg]

Took a while. It wasn't light travel time because the error introduced is too small. It was that I tried hand fitting the limb which gave a timing error which gave an angle offset from the spacecraft spin. So doing a limb search got the timing to line up. I scaled everything by its dot product to the Jupiter vector so it ended up on a plane. I dropped the extra dimension by taking the first row as one basis vector and then taking a column as another vector, made it orthonormal then projected everyting onto those vectors. It gave the first picture and I did a KD nearest neigbour search to rasterize it, second image. I kind of like the projection to a plane as I feel it makes it more like a real single camera, at least it'll behave just like a pinhole camera.

The projection to an imaginary Juno centered sphere is nice because it doesn't need any spice ray projections so takes no time and as I'm unprojecting it from the same point of view the Jupiter mapping bit isn't actually doing anything (other than some super serious finding of errors!). I feel the sphere project -> plane -> dimension reduction can easily be made into a single stage so you wouldn't actually have to do the imaginary sphere thing (Though honesty it's not that bad as it is). That should get it way faster than what I have so then a super simple pipeline can use all the hard work that went into the SPICE kernels to make nicely stitched pictures. I'm sure the nearest neighbour search can be improved on too because the data has structure so you always know which direction will get you closer, anyone know of an implementation of such a thing?

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