Appendix/Ramblings/T6CoordinatesPt2

Concentric Ellipsoidal (T6) Coordinates (Part 2)

Orthogonal Coordinates

Speculation5

Spherical Coordinates

$r\cos \theta$	$=$	$z,$
$r\sin \theta$	$=$	$(x^2+y^2{)}^{1/2},$
$\tan \phi$	$=$	$\frac{y}{x}.$

Use λ₁ Instead of r

Here, as above, we define,

${\lambda }_1^2$

$\equiv$

$x^2+q^2{y}^2+p^2{z}^2$

Using this expression to eliminate "x" (in favor of λ₁) in each of the three spherical-coordinate definitions, we obtain,

$r^2\equiv x^2+y^2+z^2$	$=$	${\lambda }_1^2-y^2(q^2-1)-z^2(p^2-1);$
${\tan }^2\theta \equiv \frac{x^2+y^2}{z^2}$	$=$	$\frac{1}{z^2}[{\lambda }_1^2-y^2(q^2-1)-p^2{z}^2];$
$\frac{1}{{\tan }^2\phi }\equiv \frac{x^2}{y^2}$	$=$	$\frac{{\lambda }_1^2-p^2{z}^2}{y^2}-q^2.$

After a bit of additional algebraic manipulation, we find that,

$\frac{z^2}{{\lambda }_1^2}$	$=$	$\frac{(1+{\tan }^2\phi )}{{{𝒟}}^2},$
$\frac{y^2}{{\lambda }_1^2}$	$=$	$\left[\frac{{{𝒟}}^2{\tan }^2\phi -p^2{\tan }^2\phi (1+{\tan }^2\phi )}{(1+q^2{\tan }^2\phi ){{𝒟}}^2}\right],$
$\frac{x^2}{{\lambda }_1^2}$	$=$	$1-q^2\left(\frac{y^2}{{\lambda }_1^2}\right)-p^2\left(\frac{z^2}{{\lambda }_1^2}\right),$

where,

${{𝒟}}^2$

$\equiv$

$[(1+q^2{\tan }^2\phi )(p^2+{\tan }^2\theta )-p^2(q^2-1){\tan }^2\phi ].$

As a check, let's set $q^2=p^2=1$, which should reduce to the normal spherical coordinate system. ${\lambda }_1^2$ $\to$ $r^2,$       and,       ${{𝒟}}^2$ $\to$ $[(1+{\tan }^2\phi )(1+{\tan }^2\theta )].$ $\Rightarrow \frac{z^2}{{\lambda }_1^2}$ $\to$ $\frac{1}{1+{\tan }^2\theta }={\cos }^2\theta =\frac{z^2}{r^2};$ $\frac{y^2}{{\lambda }_1^2}$ $\to$ $\left[\frac{(1+{\tan }^2\phi )(1+{\tan }^2\theta ){\tan }^2\phi -{\tan }^2\phi (1+{\tan }^2\phi )}{(1+{\tan }^2\phi )(1+{\tan }^2\phi )(1+{\tan }^2\theta )}\right]$   $=$ $\frac{{\tan }^2\phi }{(1+{\tan }^2\phi )}\left[\frac{{\tan }^2\theta }{(1+{\tan }^2\theta )}\right]={\sin }^2\theta {\sin }^2\phi =\frac{y^2}{r^2};$ $\frac{x^2}{{\lambda }_1^2}$ $\to$ $1-\left(\frac{y^2}{{\lambda }_1^2}\right)-\left(\frac{z^2}{{\lambda }_1^2}\right),$   $\to$ $1-{\sin }^2\theta {\sin }^2\phi -{\cos }^2\theta =-{\sin }^2\theta {\sin }^2\phi +{\sin }^2\theta ={\sin }^2\theta {\cos }^2\phi =\frac{x^2}{r^2}.$