<div dir="ltr"><div><div>Simpler often is less flexible. That's the trade-off. You want infinite flexibility, create a matrix, whether affine, Eulerian, from the discipline of geology, or otherwise. Boom, problem solved.<br>
<br>Measured/monitored systems often have these parameters as orthogonally bound parameters, e.g.:<br><br><a href="https://en.wikipedia.org/wiki/File:Rollpitchyawplain.png">https://en.wikipedia.org/wiki/File:Rollpitchyawplain.png</a><br>
<br></div><div>For these systems, the low friction between stored parameters and calculated rotations makes sense to me. This is the use case that easily comes to me, and the inspiration for the code. The most generic function already exists-- ST_Affine. I'm not looking to supplant this.<br>
</div><br></div><div>Mature 3D systems such as PovRay have both, and for a reason.<br><br><a href="http://www.f-lohmueller.de/pov_tut/trans/trans_400e.htm">http://www.f-lohmueller.de/pov_tut/trans/trans_400e.htm</a><br><a href="http://www.f-lohmueller.de/pov_tut/trans/trans_200e.htm">http://www.f-lohmueller.de/pov_tut/trans/trans_200e.htm</a><br>
<br>There's value to PostGIS also having both, whether just in my small toolkit or added to PostGIS makes no difference to my use of PostGIS.<br></div><div><br></div><div>Best,<br>Steve<br></div><div><br></div><br><div>
<div><br></div></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Mon, Dec 16, 2013 at 12:52 PM, Mike Toews <span dir="ltr"><<a href="mailto:mwtoews@gmail.com" target="_blank">mwtoews@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="im"><p dir="ltr">On 15 Dec 2013 21:50, "Stephen Mather" <<a href="mailto:stephen@smathermather.com" target="_blank">stephen@smathermather.com</a>> wrote:<br>
><br>
> Hmm, I know so little about Euler, strike, dip and rake. What are the advantages?</p>
</div><p dir="ltr">Euler angles are very well known, and have a wide range of applications[1].</p>
<p dir="ltr">Strike, dip and rake[2,3] are familiar to any geology student, and also have a wide range of applications in the earth sciences. They are similar to Euler angles. I still need to think this one through.</p>
<p dir="ltr">Both of these advanced 3d rotations can be described as affine transformation parameters. Their advantages are to perform a rigid body transform using well known angles. I think the XYZ rotation technique you are describing requires calculations of the X and Y rotation components (unless the rotation happens to align with the grid, i.e. orthogonal).</p>
<p dir="ltr">> What I do know is that it's easy now to construct a 3 axis rotation function (which also might be better handled with ST_Affine).</p>
<p dir="ltr">Easy, yes, but I'm not convinced they are useful, or even being used by othets due to their orthogonal limitations.</p>
<p dir="ltr">-Mike</p>
<p dir="ltr">[1] <a href="https://en.wikipedia.org/wiki/Euler_angles" target="_blank">https://en.wikipedia.org/wiki/Euler_angles</a><br>
[2] <a href="https://en.wikipedia.org/wiki/Strike_and_dip" target="_blank">https://en.wikipedia.org/wiki/Strike_and_dip</a><br>
[3] <a href="https://en.wikipedia.org/wiki/Rake_(geology)" target="_blank">https://en.wikipedia.org/wiki/Rake_(geology)</a></p>
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