Weird spherical mapping?

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Weird spherical mapping?

Simon Lenz
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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Re: Weird spherical mapping?

Hans-Bernhard Bröker-2
Am 13.05.2016 um 15:29 schrieb Simon Lenz:

> So as specified in the wikipedia article[1] the spherical->carthesian
> conversion should works like this:

That's overstating things a bit.  The notion that there is "the" mapping
is incorrect.  There are various ways of defining spherical coordinates,
not just one.

And Wikipedia knows that, too.  You just have to read the entire
article, not just look at a single isolated formula.

> For me this seems like an odd non-standard way of doing things.

Given there is no actual standard, nothing can really be non-standard.

gnuplot's spherical coordinates follow the conventions used in
geography, where latitude zero is at the equator, instead of a pole.

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Re: Weird spherical mapping?

Mauricio Galo
In reply to this post by Simon Lenz
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" <[hidden email]>
Para: [hidden email]
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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bring their own devices (BYOD) to work are irked by the imposition of MDM
restrictions. Mobile Device Manager Plus allows you to control only the
apps on BYO-devices by containerizing them, leaving personal data untouched!
https://ad.doubleclick.net/ddm/clk/304595813;131938128;j
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------------------------------------------------------------------------------
Mobile security can be enabling, not merely restricting. Employees who
bring their own devices (BYOD) to work are irked by the imposition of MDM
restrictions. Mobile Device Manager Plus allows you to control only the
apps on BYO-devices by containerizing them, leaving personal data untouched!
https://ad.doubleclick.net/ddm/clk/304595813;131938128;j
_______________________________________________
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