Points2d, Points3d

List of 2D points

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Value Summary

Points2d, Points3dMandatoryList of 2D points

Graphics Primitives

Description

Points2d is the list of 2D points in objects of type plot::PointList2d and plot::Polygon2d, respectively.

Points3d is the list of 3D points in objects of type plot::PointList3d and plot::Polygon3d, respectively.

One usually defines such an object p, say, via

p := plot::PointList2d([[x1, y1], [x2, y2], …]) or

p := plot::Polygon2d([[x1, y1], [x2, y2], …]), respectively.

Internally, the points are stored as the attribute

Points2d = [[x1, y1], [x2, y2], …]

and can be accessed via the slot call p::Points2d. Assigning a new list to p::Points2d changes the object p accordingly.

The corresponding statements hold for 3D point lists and polygons.

The points in the list Points2d may consist of lists with 2 elements (the x and y coordinates) or of lists with 3 elements (the x and y coordinates and the RGB color of the point).

The points in the list Points3d may consist of lists with 3 elements (the x, y, and z coordinates) or of lists with 4 elements (the x, y, z coordinates and the RGB/RGBa color of the point).

If you specify the color of one point, you must specify the colors of all other points in the list. See Example 2.

The points in the lists Points2d and Points3d can be animated.

Examples

Example 1

We define a 2D polygon with 5 points:

p := plot::Polygon2d([[0, 0], [1, 1], [1, 2], [2, 2], [2, 1]]):
plot(p):

The points in the polygon can be accessed as the Points2d attribute:

pts := p::Points2d

We change the polygon be assigning a new point list:

p::Points2d := [pts[1], pts[5], pts[2], pts[4], pts[3]]:
plot(p):

delete p, pts:

Example 2

Points2d and Points3d allow you to specify the colors of the points. For example, the following list contains two points. The plot function uses the default color for both points on the plot:

Coords := [[3, 4], [5, 5]];
plotCoords := plot::PointList2d(Coords):
plot(plotCoords, PointSize = 5)

To access and modify the list of points, use Points2d. For example, include the color of each point in the list:

plotCoords::Points2d := [[3, 4, RGB::Red], [5, 5, RGB::Green]]

Now the first point appears in red, and the second point appears in green:

plot(plotCoords, PointSize = 5)

If you specify the color of one point, you must also specify the colors of all other points in the list:

plotCoords::Points2d := [[3, 4, RGB::Red], [5, 5]]
Error: Attribute 'Points2d' in the 'PointList2d' object must be a list of lists of two expressions and an optional color value. [plot]