Simplified the Jupiter moon raytraced image demo
by using Astronomy_BackdatePosition to directly
calculate the vector while returning the backdated
time directly. This eliminates a redundant calculation
using the distance divided by the speed of light.
It makes more sense to report Jupiter's moons with
individually named structure fields rather than an array.
It reduces the overall code and documentation size,
and outside of unit testing, there are few cases
where iterating over an array of moons is more
lucid than using the names of the moons.
This is a breaking change, but hopefully very few
developers are using this function yet.
Fixing the breakage is very simple.
Reduce the number of redundant Earth nutation calculations
by passing astro_time_t values as pointers in more functions.
Nutation values can then be cached in the time parameter
and passed to other functions that can then avoid calculating
the same nutation again.
Nutation is an expensive calculation, so reducing this overhead
can dramatically speed up certain use cases.
This was only needed in C, because this is the only language
in which times are passed by value. In Python, C#, and JavaScript,
times are objects that are already passed by reference, and
they already benefit from this nutation recyling approach.
The following functions have had their parameters changed.
This is a breaking change, but in every case, the caller
usually just needs to change `time` to `&time`.
Astronomy_Rotation_EQD_EQJ
Astronomy_Rotation_EQD_ECL
Astronomy_Rotation_EQD_HOR
Astronomy_Rotation_EQJ_EQD
Astronomy_Rotation_EQJ_HOR
Astronomy_Rotation_ECL_EQD
Astronomy_Rotation_ECL_HOR
Astronomy_Rotation_HOR_EQD
Astronomy_Rotation_HOR_EQJ
Astronomy_Rotation_HOR_ECL
Astronomy_RotationAxis
Astronomy_VectorObserver
Pluto is so far away that is angular size seen from Earth
is very small. I had to tweak my internal scaling constants
so that the raytracer was able to resolve it.
Added radius data for the Sun, Moon, and remaining planets.
Test the raytracer for all other bodies except the Earth and Sun.
There is a problem with Pluto that I still need to figure out.
Fixed an issue in the doxygen-to-markdown translator I wrote
(hydrogen.js): it did not handle when one #define referred
to another #define. Created a more generic markdown expansion
that works in all cases, and creates embedded hyperlinks.
Refactored the Jupiter imager to be a generic planet imager.
Added support for drawing an image of Venus.
Verified that its extreme crescent phase looks correct
for the current date.
I will add radius constants to astronomy.h for each body I support.
The raytracer now includes the option -s (without a numeric
spin angle on the command line) to automatically calculate
the spin angle needed to bring the planet's north pole
exactly upward in the generated image.
Improved the way I create the rotation matrix that
aims the virtual camera at Jupiter. The camera still
aims exactly at Jupiter, but this time it defaults
to having the left/right pixel direction aligning
with the Earth's equator. By experiment, I can spin
the longitudinal camera axis by -10 degrees and get
a good fit with Jupiter's equatorial plane. I will
adjust this more exactly in a future commit.
Now the raytracer requires the user to pass in
both the pixel width and pixel height on the command line.
This allows for generating non-square images, which will
be necessary for the general case of imaging the moons
with respect to the planet.
I had lots of problems with using AU as my scale units.
By changing to 10000*km units, the vector equation solver
works correctly again, and I actually get an image of Jupiter
and its moons. However, it does not match the test photo:
Ganymede does not appear close to the planet, nor is there
a shadow of it on the planet. I will have to debug that
separately.
Starting to work through adaptation of existing
raytracer code to generate geometrically accurate
images of Jupiter and its moons. Not yet working,
but I believe I am at least aiming the camera in
the right direction.
