Populate Surface

Functionality

This node generates a number of random points, distributed on a given Surface according to the provided Scalar Field. It has two modes:

• Generate uniformly distributed points in areas where the value of scalar field is greater than threshold;

• Generate points according to the value of scalar field: put more points in areas where the value of scalar field is greater. More precisely, the probability of the vertex appearance at some point is proportional to the value of the scalar field at that point.

This node can make sure that generated points are not too close to one another. This can be controlled in one of two ways:

• By specifying minimum distance between any two different points;

• Or by specifying a radius around each generated points, which should be free. More precisely, the node makes sure that if you place a sphere of specified radius at each point as a center, these spheres will never intersect. The radiuses of such spheres are provided as a scalar field: it defines a radius value for any point in the space.

Inputs

This node has the following inputs:

• Surface. Surface object, on which random points must be generated. This input is mandatory.

• Field. The scalar field defining the distribution of generated points. If this input is not connected, the node will generate evenly distributed points. This input is mandatory, if Proportional parameter is checked.

• Count. The number of points to be generated. The default value is 50.

• MinDistance. This input is available only when Distance parameter is set to Min. Distance. Minimum allowable distance between generated points. If set to zero, there will be no restriction on distance between points. Default value is 0.

• RadiusField. This input is available and mandatory only when Distance parameter is set to Radius Field. The scalar field, which defines radius of free sphere around any generated point.

• Threshold. Threshold value: the node will not generate points in areas where the value of scalar field is less than this value. The default value is 0.5.

• Field Minimum. Minimum value of scalar field reached within the area defined by Bounds input. This input is used to define the probability of vertices generation at certain points. This input is only available when the Proportional parameter is checked. The default value is 0.0.

• Field Maximum. Maximum value of scalar field reached within the area defined by Bounds input. This input is used to define the probability of vertices generation at certain points. This input is only available when the Proportional parameter is checked. The default value is 1.0.

• Seed. Random seed. The default value is 0.

Parameters

This node has the following parameters:

• Distance. This defines how minimum distance between generated points is defined. The available options are:

  • Min. Distance. The user provides minimum distance between any two points in the MinDistance input.

  • RadiusField. The user defines a radius of a sphere that should be empty around each generated point, by providing a scalar field in the RadiusField input. The node makes sure that these spheres will not intersect.

  The default value is Min. Distance.

• Proportional. If checked, then the points density will be distributed proportionally to the values of scalar field. Otherwise, the points will be uniformly distributed in the area where the value of scalar field exceeds threshold. Unchecked by default.

• Random Radius. This parameter is available only when Distance parameter is set to RadiusField. If checked, then radiuses of empty spheres will be generated randomly, by using uniform distribution between 0 (zero) and the value defined by the scalar field provided in the RadiusField input. Unchecked by default.

When Proportional mode is enabled, then the probability of vertex appearance at the certain point is calculated as P = (V - FieldMin) / (FieldMax - FieldMin), where V is the value of scalar field at that point, and FieldMin, FieldMax are values of corresponding node inputs.

Outputs

This node has the following outputs:

• Vertices. Generated vertices.

• UVPoints. Coordinates of generated vertices in surface’s U/V space. Third coordinate of these points is always zero.

Example of usage

Distribute points on a Moebius band according to some attractor field:

Example of “Radius Field” mode usage: