[SciPy-Dev] [GSOC 2018 Project Thread]: Rotation formalism in 3 dimensions

[Aditya Bharti]

Hi all,
This week was mainly spent in implementing the `as_euler` function, which
is responsible for returning an Euler angle representation for the
underlying rotation. The implementation took some time (we're still ironing
out the gritty details) for two major reasons:

   - There are a few conventions for Euler angles and rotations in general.
   Figuring out which convention this paper
   <https://arc.aiaa.org/doi/abs/10.2514/1.16622> followed and then
   extending the algorithm to extrinsic and intrinsic rotations was time
   consuming.
   - The infamous *Gimbal Lock*. While converting from Euler angles this
   presents no problems, converting to euler angles presents issues. In this
   case it is not possible to uniquely determine all the angles and algorithms
   become numerically unstable, which leads to small tweaks (which should work
   in theory) breaking our implementation by changing the sign of small
   quantities close to zero.

This function is the last representation related function of the class,
after which we move on to compositions, applications, and inversions of
general Rotation objects. You can go through the code
<https://github.com/adbugger/scipy/tree/rotation/scipy/spatial/transform>
or check out my blog <https://blogs.python-gsoc.org/aditya-bharti> to
follow along. Stay tuned for more updates.

Thanks,
Aditya

On Wed, 30 May 2018 at 02:51, Aditya Bharti <adibhar97 at gmail.com> wrote:

> Hi all,
> Continuing the work so far, the following have been implemented this week:
>
>    - `from_rotvec`, `as_rotvec`: Representing Euler angles as rotation
>    vectors, with appropriate Taylor series expansions for small angles
>    - `from_euler`: Initialization from Euler angles, along with a string
>    based axis sequence specification. Refer to docs for more details.
>
> As always, the project lives here
> <https://github.com/adbugger/scipy/tree/rotation/scipy/spatial/transform>,
> and my personal experiences can be found on the blog
> <https://blogs.python-gsoc.org/aditya-bharti>.
>
> Thanks,
> Aditya
>
> On Sun, 20 May 2018 at 13:28, Phillip Feldman <phillip.m.feldman at gmail.com>
> wrote:
>
>> When you say "discrete cosine matrix", I think that you mean "direction
>> cosine matrix" (see
>> https://en.wikiversity.org/wiki/PlanetPhysics/Direction_Cosine_Matrix).
>>
>> Phillip
>>
>> On Sat, May 19, 2018 at 12:23 PM, Aditya Bharti <adibhar97 at gmail.com>
>> wrote:
>>
>>> Hi all,
>>> So this concludes week 1 of GSoC 2018. I must say it was a great
>>> learning experience and I invite you all to check out my account of this
>>> week on the blog <https://blogs.python-gsoc.org/aditya-bharti/>. This
>>> email is more of a technical update.
>>>
>>>    - So, the main `Rotation` class will live under a new sub module
>>>    `scipy.spatial.transform`.
>>>    - Conversion between quaternions and discrete cosine matrices was
>>>    implemented.
>>>    - The rotation class now supports `from_quaternion`, `from_dcm`,
>>>    `as_quaternion` and `as_dcm`, with support for multiple rotations in one
>>>    call.
>>>
>>> The project currently lives in my own fork of scipy here
>>> <https://github.com/adbugger/scipy/tree/rotation/scipy/spatial/transform>.
>>> Stay tuned for more updates!
>>>
>>> Best,
>>> Aditya
>>>
>>> On Wed, 2 May 2018 at 21:03, Aditya Bharti <adibhar97 at gmail.com> wrote:
>>>
>>>> Hi Nikolay,
>>>>
>>>> I've used Wordpress only once before, so I don't know much about it.
>>>> From my limited experience, it is extremely customizable. You can customize
>>>> every thing from the look and feel to SEO characteristics. There are
>>>> apparently a lot of wordpress plugins for these kind of tasks. For this
>>>> particular blog, PSF had already setup an account for me with a site on it.
>>>> All I had to do was click on the 'New' button and open up the new post
>>>> page. There's a field for a header and body text, with options for adding
>>>> audio, video and hyperlinks.
>>>>
>>>> As regards to the post itself, sure I'll expand it with a brief
>>>> overview, motivation and an example. Note that the example will only show
>>>> sample usage, not any internals. I plan to borrow heavily from my proposal
>>>> for this purpose, I hope that's ok.
>>>>
>>>> Regards,
>>>> Aditya
>>>>
>>>> On 2 May 2018 at 19:54, Nikolay Mayorov <nikolay.mayorov at zoho.com>
>>>> wrote:
>>>>
>>>>> Hi, Aditya!
>>>>>
>>>>> Glad that you set up the blog and good job on setting up the
>>>>> documentation build as well.
>>>>>
>>>>> Curious, what is this blogging platform like? How do you create posts
>>>>> in it?
>>>>>
>>>>> As for your first post: while not strictly necessary I think it would
>>>>> be nice to see a more thorough introductory post with a brief overview,
>>>>> motivation and/or an example. Do you want to work on it?
>>>>>
>>>>> Best,
>>>>> Nikolay
>>>>>
>>>>>
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>>>>
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