[Orekit Developers] SOCIS 2011 and Android

[Alexis ROBERT <alexis.robert@gmail.com>]

Hi,

I know this is basically a copy-paste of the form I've submitted on
the SOCIS website, but on the SOCIS website we can't have feedback and
adapt the submission to your needs.

I'm very interested in the task "Create a space flight dynamics pocket
calculator application for android mobile devices" as I've never
ported an existing framework to Android, and I think it's pretty
exciting. In fact, I've already did a little Android application but
it was not very interesting technically speaking as it was a
dictionary (excepting the C/JNI engine to speed up index parsing for
low-end phones with small CPUs). I've also made a little patch on the
Android's SMS app which has been merged by Google, but that's not very
related to this task :)

In order to test the feasibility of porting Orekit to Android, I've
already done some testing, and I've been successfully able to build
Dalvik bytecode from Orekit and Apache Common Math jar files, and to
run src/tutorials/fr/cs/examples/frames/Frames1.java on my Android
phone.

# time dalvikvm -classpath test-orekit.jar Test
time doppler (m/s)
2008-10-01T00:00:00.000 -2925.114
2008-10-01T00:10:00.000 -3069.084
2008-10-01T00:20:00.000 -1331.910
2008-10-01T00:30:00.000 1664.611
2008-10-01T00:40:00.000 3143.549
2008-10-01T00:50:00.000 2832.906
2008-10-01T01:00:00.000 1556.662
2008-10-01T01:10:00.000 -140.889
2008-10-01T01:20:00.000 -1860.637
2008-10-01T01:30:00.000 -3195.728
2008-10-01T01:40:00.000 -3538.053
real 0m 55.71s
user 0m 43.80s
sys 0m 1.47s
# uname -a
Linux localhost 2.6.37.6-cyanogenmod-01505-g81b06a8 #1 PREEMPT Sat Jun
18 13:14:06 EDT 2011 armv7l GNU/Linux

This was run on a Nexus One on Android 2.3 (with JIT enabled). As this
was not the first run, data was in cache and so the latency due to
reading data from the sdcard should not be accounted.

There is two main issues I may encounter. The first would be the
physics part, in fact I'm just undergraduate in Physics, and I might
not be able to fully understand some computations and I hope this will
not be a problem. In fact if I just have some pointers on how to do
the computation in Java it would be fine.

The second would be performance. In fact, phones CPU are very slow
even if the Dalvik VM tries to reduce this bottleneck. For instance,
Frames1.java takes 55 seconds to run on a Nexus One (1GHz ARMv7 CPU
with 512MB of RAM) when it takes 4 seconds on a Core 2 Duo Linux
laptop (T8100 2.10GHz with Java 1.7.0-b147 on ArchLinux). It would be
useful to profile Orekit and identify the bottlenecks and try to
optimize them to reduce garbage collector stress, or such other things
which are not noticeable on a desktop computer but are highly
noticeable on an ARM CPU.

In fact my proposed planning would be slightly different from the one
which is published on the wiki (the required days are *very*
approximative) :

1. Understand the list of computation needed in the final application
and write a little text-mode test app in J2SE (~7 days)
2. Draw the UI on paper (tablet+phone) and submit it to the
mailing-list for approval (~3 days)
3. Make the actual Android application (~7 days)
4. Move the computations in a Worker thread to make the UI responsive,
while making sure that rotation still works (this is not as easy as it
first sounds, mixing rotation and worker threads are not an easy task
on Android as a rotation deletes the window class and keeps the worker
thread working, but there is ways to fix this) (~2 to 3 days)
5. Identifying bottlenecks and try to fix them (rest of the time)

Thanks :)

Alexis Robert