The vgtest script allows checking for memory errors in
Astronomy Engine using valgrind. This helped me find
a bug where I was using uninitialized memory.
The PlutoStateTable was slightly different when generated
in Linux and Windows, because there was so much precision
after the decimal point. Reduced precision until Linux
and Windows generated the exact same output.
Instead of remembering the most recent 3 segments of Pluto's orbits,
cache up to all 40 segments within the year span 0000..4000.
Use dynamic memory to allocate them instead of static memory.
Added Astronomy_Reset() to free memory before exit.
Also reduced stack usage by sharing bary[5] more.
Eliminated a redundant call to MajorBodyBary() when
calculating one-way outside the bounds of PlutoStateTable.
There were two places where I was searching for table entries.
I realized I can just directly calculate the same indexes.
This makes the code smaller and faster.
To make Pluto calculations have a low amortized time cost,
calculate up to 3 segments between adjacent pairs of
pre-calulcated states and recycle them. Do linear ramp
fade-mixing between them.
Currently, something is wrong with this because it fails
by inaccurately calculating horizontal coordinates of Pluto
in one test. I'm not sure what's going wrong there yet,
but likely related to multiple calls via search.
This is a happy compromise between speed and accuracy.
Solidified this as a #define PLUTO_DT, which will allow
me to do compile-time math to establish an array size for
an internal buffer of lazy-computed dt increments between
most recently requested segment endpoints.
Now we are getting somewhere!
Using the mean acceleration over the interval seems so much
better than the complicated calculus thing I did.
Now I am using a very large time step: 500 days,
with an error less than 0.2 arcminutes.
C PlutoCheck: dt = 500.000000
C PlutoCheck: 2049-12-19T12:00:00.000Z = 18250.000000 UT = 18250.001076 TT
C PlutoCheck: calc pos = [ 37.4373396436339121, -10.2445033319559062, -14.4764587025278448]
C PlutoCheck: ref pos = [ 37.4377303529113306, -10.2466292445590774, -14.4773101309873091]
C PlutoCheck: del pos = [ -0.0003907092774185, 0.0021259126031712, 0.0008514284594643]
C PlutoCheck: diff = 2.323163e-03 AU, 0.198 arcmin
Allow passing in the dt value as an environment variable PLUTO_DT:
$ PLUTO_DT=100 ./ctest pluto
C PlutoCheck: dt = 100.000000
C PlutoCheck: 2049-12-19T12:00:00.000Z = 18250.000000 UT = 18250.001076 TT
C PlutoCheck: calc pos = [ 37.4506659151144774, -10.2638146514621269, -14.4865003148403595]
C PlutoCheck: ref pos = [ 37.4377303529113306, -10.2466292445590774, -14.4773101309873091]
C PlutoCheck: del pos = [ 0.0129355622031468, -0.0171854069030495, -0.0091901838530504]
C PlutoCheck: error = 2.339073e-02 AU, 1.989 arcmin
Default to dt = 50 days.
I had a bug in the calculation of the Solar System Barycenter.
The position and velocity vectors were both backwards.
This caused the barycentric Sun to be in the wrong place.
C PlutoCheck: 2049-12-19T12:00:00.000Z = 18250.000000 UT = 18250.001076 TT
C PlutoCheck: calc pos = [ 37.4386594210222654, -10.2474739785185811, -14.4777836541558340]
C PlutoCheck: ref pos = [ 37.4377303529113306, -10.2466292445590774, -14.4773101309873091]
C PlutoCheck: del pos = [ 0.0009290681109348, -0.0008447339595037, -0.0004735231685249]
C PlutoCheck: error = 1.342001e-03
I didn't implement the math I had derived on paper exactly right.
There was one place where I meant to have (dt^3 / 6), but I had (dt^2 / 6).
This has only a tiny effect on the error. I know this can work better,
so I'm still searching for the real problem.
C PlutoCheck: 2049-12-19T12:00:00.000Z = 18250.000000 UT = 18250.001076 TT
C PlutoCheck: calc pos = [ 37.3682426267669996, -10.0216432448322834, -14.3724661626442582]
C PlutoCheck: ref pos = [ 37.4377303529113306, -10.2466292445590774, -14.4773101309873091]
C PlutoCheck: del pos = [ -0.0694877261443310, 0.2249859997267940, 0.1048439683430509]
C PlutoCheck: error = 2.577586e-01
I picked a worst-case starting time that is halfway between
two entries in the PlutoStateTable[]. This requires the most
iterations to calculate. Now I have a better metric for
position accuracy:
C PlutoCheck: 2049-12-19T12:00:00.000Z = 18250.000000 UT = 18250.001076 TT
C PlutoCheck: calc pos = [ 37.3682426469732860, -10.0216428456503461, -14.3724660445065933]
C PlutoCheck: ref pos = [ 37.4377303529113306, -10.2466292445590774, -14.4773101309873091]
C PlutoCheck: del pos = [ -0.0694877059380445, 0.2249863989087313, 0.1048440864807159]
C PlutoCheck: error = 2.577590e-01
Clearly I still have a lot of work to do!
Got 'ctest pluto' error down to 5.675183e-05 AU.
I was adding vectors when I should have been subtracting,
to find heliocentric Pluto from barycentric Pluto.
The 'ctest pluto' command was testing against slightly wrong coordinates.
Added 'generate topcalc' command to print out exact TOP2013 values.
Used those values as the reference coordinates in 'ctest pluto'.
Sadly, this increased the measured error from 1.347e-02 AU to 1.412e-02 AU.
When finalizing the position of Pluto, I need to convert
barycentric coordinates to heliocentric coordinates.
I do this by adding the barycentric location of the Sun
to the barycentric location of Pluto to obtain the
heliocentric location of Pluto. But I was using the Sun
coordinates from the simulation starting point, not
at the final time.
This decreases the AU error from 1.369e-02 to 1.347e-02.
I'm still looking for the rest of the error.
I know this code currently fails unit tests, and will take far too
long if attempted. Therefore, I'm turning off pluto_integrator.
I will turn it back on when I believe it's working.
I just want to be able to back up my code offsite while I'm still
developing it.
I wasn't initialzing the acceleration vector in the value returned
by GravSim(). I'm not sure how any of this ever worked!
Found it by using valgrind.
There is no apparent advantage to looping for convergence in GravSim().
Also, it looks like I can use a much larger dt = 10 days.
Added PlutoStateTable to C code generator.
This is a table of known correct [tt, pos, vel] tuples for Pluto,
calculated using TOP2013. These serve as seed points from which
to integrate Pluto's motion.
Added PlutoCheck() function to ctest, just to get going.
I have a lot more peformance work to do in order to make
the full blown unit test to finish in a reasonable amount of
time.
Changes in astronomy.c:
Added some generic "terse vector" support.
A terse vector contains 3 components and nothing else.
This is handy for implementing compact formulas for various
vector expressions.
Created enhanced VSOP87 calculations that provide
velocity vectors as well as position vectors for
the Sun, Jupiter, Saturn, Uranus, and Neptune.
These are the "major" bodies that have significant
effects on the motion of Pluto. Also used to convert
heliocentric coordinates to barycentric coordinates.
Implemented first version of the integrator logic.
It is not accurate enough yet, and it is far too slow.
I need to debug the accuracy first, then I will work on
making it faster.
I was experimenting with an alternative way to calculate Pluto's position.
That idea didn't work out, but in the process, I did make some changes
I want to keep:
1. A typecast in generate/codegen.c that eliminates a build warning
in Windows (Visual Studio 2015).
2. Expanded generate/vsop/vsop.c to calculate both position and velocity
vectors. This was tricky to get working, and could come in handy.
I had to require('./astronomy.js') instead of require('astronomy.js')
to get the nodejs demos working, now that I maintain a redundant
copy of astronomy.js in the demo directories.
Windows does not support relative links in Git by default.
This broke the first-time experience for Windows users.
From now on I will maintain copies of the astronomy.js
and astronomy.py in the demo folders, so that the demos
will work on Windows immediately after cloning the repo.
Using Linux relative links to astronomy.py and astronomy.js
from the demo directories just doesn't work in Windows.
This creates a stumbling block for first-time users.
To make it easier for people to get started, I will just
make redundant copies in other directories as needed.
It is better to use a little extra disk space -- hard drives are cheap!
This is the first step: get rid of the links.
When I added support for pseudo-bodies like SSB
(Solar System Barycenter), it broke the positions.html demo.
Use an explicit list of the bodies to be calculated.
I should probably get rid of Astronomy.Bodies, because it
seems to invite bugs like this. I will think more about that.
Also, there was no way to manually edit the time.
Added a checkbox called "Automatic" that toggles whether
the time is updated automatically every second or
is entered by the user.
Persist the checkbox and edited time in the saved options.
In the JavaScript version, check throughout for valid
finite numeric/boolean values as needed.
This should make debugging a lot easier for everybody.
In the unit tests for all languages, also check for infinite
results, not just NaN.
I discovered that JS Astronomy.NextLocalSolarEclipse() was broken:
It was trying to call a nonexistent function.
Fixed it, and added unit test that would have caught the breakage.
Fixed mistakes in JS documentation for the field names of the
Observer class.
Instead of turning off all "expensive optimizations" in gcc,
I found I can achieve consistent calculation results on
64-bit ARM processors by turning off just the "fp contract"
optimization.
This optimizer is actually supposed to produce *more* accurate
results, but the effect is to produce results that differ
across languages/processors. For the sake of the unit tests,
I have decided it must be turned off in ctest and generate.
It turns out that in gcc 9.3.0 on aarch64, the "expensive optimizations"
were causing incorrect calculations. I resumed using -O3 but with
expensive optimizations turned off. Now all unit tests pass again.
Fixed some build warnings that occur on various gcc
optimization levels, and only on this version of gcc.
For now, build ctest with fewer optimizations: -O1
instead of -O3. This is because -O3 and -O2 cause
excessive errors in 'ctest diff' of the order
1.0e-9, where I usually get 1.0e-12. I will have to
come back and figure out exactly which optimization(s)
are causing the problem and turn them off specifically.
This also means I need to document the dangerous optimizations
for people who are using the C version of Astronomy Engine.
When 'ctest diff' fails because of excessive numeric error,
print out the two lines of input text that had the worst
numeric error. This really helps on the Raspberry Pi
where memory is at a premium, and it's hard to open the
full output files using vi.
Version 9.3.0 of gcc has extra warnings that detect snprintf
truncations and use of possibly uninitialized variables.
Fixed some warnings of both types.
I'm working on a Solar System gravity simulation.
I need very precise position and velocity data for the major
Solar System bodies. I want to write the simulator as a browser-
based animation, so I will code it in JavaScript. This JSON
generator is a bootstrap to provide the initial solar system
state, plus it allows testing how accurate the simulation
is as it unfolds. Plus it may be useful for any program that
can parse JSON easily.
Added Astronomy_FormatTime to the topic index.
Reworded text to avoid "as explained above", because it turns
out the generated documentation does not always put things
in the same order they appear in the source code comments.
It's surprisingly tricky to print a time rounded to the
nearest millisecond, second, or minute using the C code.
I saw a case where positions.c printed '2020-07-09 04:29:60'.
Because printing a date/time is a basic need of an astronomy program,
I added the new function Astronomy_FormatTime to do this.
All the demo programs use this new function, which required
me to update the correct reference output for the unit tests.
