Re: [Gnuplot-info] Weird spherical mapping?

[Mauricio G. (D. de Cartografia) <ga...@fc...>]

Simon

In your data set you have the angles “theta” and “phi”. To know the correct set of equations you should inform two thinks:

- Your “theta” angles is the horizontal angle or de vertical angle?
- Your vertical angle starts on the vertical axis Z or in the horizontal plane?

By knowing these answer it will be possible to define the equations without doubt.

M. Galo

----- Mensagem original -----
De: "Simon Lenz" <s_l...@cs...>
Para: gnu...@li...
Enviadas: Sexta-feira, 13 de maio de 2016 10:29:15
Assunto: [Gnuplot-info] Weird spherical mapping?

Hello,

I'm trying to plot some 3D points defined in spherical coordinates.
(like this
https://upload.wikimedia.org/wikipedia/commons/thumb/6/69/Kugelkoord-def.svg/300px-Kugelkoord-def.svg.png)

So as specified in the wikipedia article[1] the spherical->carthesian
conversion should works like this:
      x = r * sin(theta) * cos(phi)
      y = r * sin(theta) * sin(phi)
      z = r * cos(theta)

My problem is now, that as documented in (set mapping spherical)
gnuplot does the spherical->carthesian conversion like this:
      x = r * cos(theta) * cos(phi)
      y = r * sin(theta) * cos(phi)
      z = r * sin(phi)

For me this seems like an odd non-standard way of doing things. But
on the other side, I'm not really familiar with the whole thing. 

How can I achieve an output with correct corrdinates for my data?

thanks in advace,

Simon

---------

script:
	set xlabel "x"
	set ylabel "y"
	set zlabel "z"
	set xrange [-1:1]
	set yrange [-1:1]
	set zrange [-1:1]
	set mapping spherical
	set angles degrees
	splot 'test.dat'

	pause -1

data:
	#theta phi r
	0 0 1
	90 180 1

[1]
https://en.wikipedia.org/wiki/Spherical_coordinate_system#Cartesian_coordinates

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