Maxima – 268 – draw – 15

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Continuo da qui, copio dal Reference Manual, PDF scaricabile da qui, sono a p.829.

palette
Default value: color.

palette indicates how to map gray levels onto color components. It works together with option enhanced3d in 3D graphics, who associates every point of a surfaces to a real number or gray level. It also works with gray images. With palette, levels are transformed into colors.

There are two ways for defining these transformations.

First, palette can be a vector of length three with components ranging from -36 to +36; each value is an index for a formula mapping the levels onto red, green and blue colors, respectively:

     0: 0               1: 0.5           2: 1
     3: x               4: x^2           5: x^3
     6: x^4             7: sqrt(x)       8: sqrt(sqrt(x))
     9: sin(90x)       10: cos(90x)     11: |x-0.5|
    12: (2x-1)^2       13: sin(180x)    14: |cos(180x)|
    15: sin(360x)      16: cos(360x)    17: |sin(360x)|
    18: |cos(360x)|    19: |sin(720x)|  20: |cos(720x)|
    21: 3x             22: 3x-1         23: 3x-2
    24: |3x-1|         25: |3x-2|       26: (3x-1)/2
    27: (3x-2)/2       28: |(3x-1)/2|   29: |(3x-2)/2|
    30: x/0.32-0.78125 31: 2*x-0.84     32: 4x;1;-2x+1.84;x/0.08-11.5
    33: |2*x - 0.5|    34: 2*x          35: 2*x - 0.5
    36: 2*x - 1

negative numbers mean negative colour component. palette = gray and palette = color are short cuts for palette = [3,3,3] and palette = [7,5,15], respectively.

Second, palette can be a user defined lookup table. In this case, the format for building a lookup table of length n is palette=[color_1, color_2, ..., color_n], where color_i is a well formed color (see option color) such that color_1 is assigned to the lowest gray level and color_n to the highest. The rest of colors are interpolated.

Since this is a global graphics option, its position in the scene description does not matter.

It works together with option enhanced3d in 3D graphics.

(%i1) draw3d(
        enhanced3d = [z-x+2*y, x, y, z],
        palette = [32, -8, 17],
        explicit(20*exp(-x^2-y^2)-10, x, -3, 3, y, -3, 3))$

268-1

It also works with gray images.

(%i2) im: apply(
        'matrix,
          makelist(makelist(random(200), i, 1, 30), i, 1, 30))$

(%i3) /* palette = color, default */
      draw2d(image(im, 0, 0, 30, 30))$

268-2

(%i4) draw2d(palette = gray, image(im, 0, 0, 30, 30))$

268-3

(%i5) draw2d(palette = [15, 20, -4],
        colorbox = false,
        image(im, 0, 0, 30, 30))$

268-4

palette can be a user defined lookup table. In this example, low values of x are colored in red, and higher values in yellow.

(%i6) draw3d(
        palette = [red, blue, yellow],
        enhanced3d = x,
        explicit(x^2+y^2, x, -1, 1, y, -1, 1))$

268-5

See also colorbox and enhanced3d.

point_size
Default value: 1.

point_size sets the size for plotted points. It must be a non negative number. This option has no effect when graphic option point_type is set to dot.

This option affects the graphic object points in either gr2d and gr3d.

(%i7) draw2d(points(makelist([random(20), random(50)], k, 1, 10)),
        point_size = 5,
        points(makelist(k, k, 1, 20), makelist(random(30), k, 1, 20)))$

268-6

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