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Re: [mg4368] ParametricPlot3D: shading?
Posted:
Jul 19, 1996 2:59 AM


lawry@maths.ox.ac.uk (James Lawry) [mg4368] ParametricPlot3D: shading?
Is concerned that ParametricPlot3D[{x, y, 1, Hue[x]}, {x, 0, 1}, {y, 0, 1}] colors according to the lighting, while Plot3D[{1, Hue[x]}, {x, 0, 1}, {y, 0, 1}] colors according to the directive Hue[x].
James,
Firstly, we can color ParametricPlot3D[..] according to directive by turning the lighting off. ParametricPlot3D[{x, y, 1, Hue[x]}, {x, 0, 1}, {y, 0, 1}, Lighting > False ]
The reason that we don't need to do this for Plot3D[...] and why it is hidden seems to lie in the following.
Although we have sg = Plot3D[{1, Hue[x]}, {x, 0, 1}, {y, 0, 1}] SurfaceGraphics colored according to the directive Hue[x], with, surprisingly Options[sg, Lighting] {Lighting > True}
The SurfacGraphics object stores only matrices of heights color directives, NOT the polygons that appear in the display.Check with List@@sg
Presumably the polygons must be constructed to be displayed. Let's simulate this by converting sg to a Graphics3D object
sg3d = Graphics3D[sg] Graphics3D Check that the polygons are there: List@@sg3d
AND note that the option Lighting > False has been automatically prepended to the list of options. We can see this without searching all of the code:
Options[sg3d, Lighting] {Lighting > False, Lighting > True}
(1) We can see the graphics code by using InputForm instead of the List@@ trick (which I used to emphasise that no processing was involved)
InputForm[sg]
(2) It makes the preceding more manageable if we reduce the number of plot points, by using PlotPoints > 3 for example.
(3) Try Show[sg3d, Lighting > True]
Allan Hayes hay@haystack.demon.co.uk



