Inputs
This is the spline geometry that you like to evaluate.
In this menu you select the type of information you want to output. For example, you can choose between Colors, the Corner status, Point Positions, Tangents and Weights.
Please note that the information on Normals and the UV coordinates are not used by default on a spline geometry. Nevertheless, these properties can also be added to a spline geometry via the Geometry Property Set node, for example, and then output interpolated via this node. You use the Evaluation Parameter to address the position at which the selected information is to be calculated as a percentage of the length of the spline geometry or one of its segments. It should be noted that only the information available at the spline points is interpolated. This means, for example, that the interpolation of point positions does not necessarily lead to a position that lies on the spline curve between these points, but rather on a straight line that connects the two points. The same applies to the output of interpolated tangents. Consider the following small example:
Here, a Circle is evaluated as spline geometry. The actual points of the spline, between which the information is interpolated by the node, are marked in red. In this particular example, the Evaluation Parameter 12.5% is used to calculate the exact center between the spline points marked with black circles. The result of a Tangent and Point Position evaluation can be seen on the blue point on the left. On the right you can see the corresponding result when using the Evaluate Spline node, which actually calculates a position and a tangent at the actual position of the spline.
As can be seen on the left-hand side of the figure above, the Spline Property Interpolate node performs a linear interpolation of the two read-out point properties between which the position of the Evaluation Parameter is located. In the case of tangents and positions, this results in interpolated data that may deviate from the exact values of the spline section. If you require exact positions and tangents along a spline, it is therefore better to use the Evaluate Spline node as an alternative, which otherwise uses the same Evaluation Parameter.
- Point Positions: A 3D vector is output here, which outputs an interpolated position between neighbouring spline points. This position is addressed as a percentage via the Evaluation Parameter. Note the deviation documented in the figure above, which can result from the linear interpolation of the available point values.
- Normals: Normals are only used on a mesh geometry, e.g. to influence the shading of the surface. This property can therefore neither be added nor evaluated on a spline geometry. The separate node Mesh Property Interpolate is available for the interpolated reading of normals on a mesh geometry.
- Color Alpha: Color values including available alpha values can be output here. Color values can be assigned to the points of the geometry, e.g. via a Vertex Color Tag or via nodes, such as Geometry Property Set.
- UV: Splines do not have UV coordinates by default and cannot use them directly. Nevertheless, UV coordinates can also be added to a spline geometry, e.g. by means of a Geometry Property Set node, and also output calculated interpolated between the spline points.
- Weight: Weight values can be assigned via a Vertex Map tag or via a Geometry Property Set node, for example, and contain values between 0.0 and 1.0 for the points of a geometry.
- Tangent: Tangents are saved in pairs per point of the spline, as a so-called Tuple. One vector indicates the tangent in the direction of the previous and a second vector indicates the direction of the subsequent curve area at each spline point. The output tangent tuple can be resolved into the two individual tangent vectors using a Decompose Container node. Please note that tangents can also be output for hard interpolated spline points. These then each have the length 0 and are then output as 0,0,0. It should also be borne in mind that the tangents of the neighboring spline points are interpolated linearly and therefore do not necessarily correspond to the actual tangent of a spline section. The figure above demonstrates this possible deviation, which results from the linear interpolation of the point tangents. If you require an exact tangent along the spline geometry, it is therefore better to use the Evaluate Spline node. Here too, the exact position required along the curve can be addressed via an Evaluation Parameter percentage value.
- Corner: These are bool values that determine whether a spline point should have a tangent (value = false) or whether it is a hard interpolated point (value = true). Since the Bool data type only knows these two states, there can be no soft interpolation of the values between the adjacent spline points. The output will jump hard to the value that is closest to the Evaluation Parameter position along the spline.
Data records, e.g. for UV coordinates, Weights or Vertex Colors, can exist several times and can be distinguished from each other by a name. If no name has been specified, the first data record of the selected type is read out.
Use this value to specify the position along the spline that is to be evaluated. To be sure that the position is really calculated proportionally to the length of the spline, you can activate the Uniform option. In this way, a value of 50% also corresponds to the middle of the spline read out.
If there are several segments on the spline, enter the index number of the desired segment here. Remember that the first segment always has the number 0. Activate All Segments if you want to evaluate the total length of a spline with several segments.
Activate this option to use an uniform distribution of intermediate points for the evaluation of the spline. This ensures that the Evaluation Parameter is always applied proportionally to the length of the spline.
Activate this option if you like to evaluate values along a spline that consist of multiple segments.