# [racket] Plotting in the x and y dimensions

 From: Neil Toronto (neil.toronto at gmail.com) Date: Tue Apr 1 04:09:47 EDT 2014 Previous message: [racket] Confused about define-values(-for-export) forms in define-signature Next message: [racket] Racket/class, inherit-field all Messages sorted by: [date] [thread] [subject] [author]

```Beware the zombie thread!

Kieron: I've just pushed an update to Plot to give it a proper 3D
engine. It should be able to handle arbitrary 3D scenes now. In
particular, plotting surfaces over each axial plane, as in your example
program, will always look right no matter how the surfaces intersect.

Here's a new example from Plot's introduction. It's a plot of two
partially transparent, intersecting spheres, using `isosurface3d':

http://imgur.com/dzJL7ry

Now that 3D rendering is robust, I'm considering new kinds of plots and
documenting the rendering API. (Though I may convert Plot to Typed
Racket first now that Asumu has made it possible.)

Neil ⊥

On 09/17/2013 10:55 AM, Neil Toronto wrote:
> Interesting and useful!
>
> Aside from a looming graduation deadline (for a PhD - yeah, BYU is
> weird), the only thing keeping me from generalizing the surface
> renderers like this is depth sorting. Because of transparency, and
> because plots have to be rendered in non-OpenGL contexts (e.g. PDFs, in
> which there's no depth buffer), polygons have to be sorted by their
> distance from the viewer and drawn back-to-front. I didn't initially
> take the time to do it properly. The current implementation sorts
> polygons by the centers of their bounding boxes, which sorts correctly
> for discretized f(x,y) surfaces and other x,y-grid-like things.
>
> IIRC, its correctness depends on the x,y grid, and the view vector
> always pointing at the top of the z-min plane. It doesn't guarantee
> proper depth sorting otherwise, and I apologize for that.
>
> If/when you get bad sorting, you could generate an isosurface3d renderer
> to draw the surface where the signed y or z distance from your function
> is zero, like this:
>
>    (define (f x z) (* x z))
>    (plot3d (isosurface3d (λ (x y z) (- y (f x z)))
>                          0
>                          -1 1 -1 1 -1 1))
>
> This is basically how `polar3d' is implemented. Because it chops the
> entire plot into cubes, the produced polygons meet the depth sorter's
> assumptions. It's a lot slower than your solution, though, and ends up
> drawing extraneous contour lines.
>
> I would like to eventually make the depth sorting robust.
>
> Neil ⊥
>
> On 09/16/2013 05:51 AM, Kieron Hardy wrote:
>> In the plot collection, it currently seems possible to plot only in the
>> z-dimension, i.e. plot functions where the z value is derived from some
>> f(x,y)
>>
>> I needed the ability to plot functions where: x is derived from some
>> f(y,z); and y is derived from some f(x,z). In case it is useful to
>> others, my solution is on github at
>> https://github.com/khardy/racket-surface3d.git
>>
>> I copied intact the existing surface3d form to create surface3d/z (i.e.
>> calculate z from x and y) and then derived two new forms, surface/x and
>> surface/y, that calculate values for the x and y dimensions
>> respectively. Some refactoring could be useful, since the three forms
>> differ only in the various permutations of which dimension's min's and
>> max's and values get used where, but maybe not worth the effort for just
>> those three.
>>
>> The new forms are in surface3d-xyz.rkt. The demo
>> (surface3d-xyz-demo.rkt) below show drawing three surfaces, one each for
>> part of the x, y, and z axes around the origin.
>>
>> Cheers,
>>
>> Kieron.
>>
>> ****
>>
>> #lang racket/base
>>
>> (require plot)
>> (require "surface3d-xyz.rkt")
>>
>> (plot3d
>>    (list
>>      (surface3d/x
>>        (lambda (y z) 0) ; plot x = 0
>>        -2 2 ; y-min/y-max
>>        -2 2 ; z-min/z-max
>>        #:label "x = 0"
>>        #:color 3
>>        )
>>      (surface3d/y
>>        (lambda (x y) 0) ; plot y = 0
>>        -2 2 ; x-min/x-max
>>        -2 2 ; z-min/z-max
>>        #:label "y = 0"
>>        #:color 5
>>        )
>>      (surface3d/z
>>        (lambda (x y) 0) ; plot z = 0
>>        -2 2 ; x-min/x-max
>>        -2 2 ; y-min/y-max
>>        #:label "z = 0"
>>        #:color 7
>>        )
>>      )
>>    #:x-min -3 #:x-max 3
>>    #:y-min -3 #:y-max 3
>>    #:z-min -3 #:z-max 3
>>    #:altitude 25
>>    )
>>
>>
>>
>> ____________________
>>    Racket Users list:
>>    http://lists.racket-lang.org/users
>>
>

```

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