# Probe Modifiers

Home >> Rigging & Animation >> Modifiers >> Probe Modifiers Comments (3) Curve Probe
The 'Curve Probe' is a channel modifier that allows users to sample various attributes from a target curve and apply the sampled value to another channels input. This could be useful to, for instance, constrain an object along a path without actually using a Constraint modifier or, for Shading, it could be used to create an adjustable seams when used with displacements.

When used in a rigging/animation context, a 'Locator' item is generally used as the Input (sampling) Position, connecting its 'World Position' matrix into the probes 'Input position' matrix. When used this way, the value generated by the probe represents the closest position along the nearest curve to the Locator. The output value is constantly updated as the Locator item moves. When used in a shading context, A 'Matrix Construct' modifier should be used to convert the 'Texture Coordinates' channel from a Texture Locator into the Probes 'Input Position' so it can be read on a per-sample basis.  Curve Probe--

Curve ID: This value is used to designate a specific curve, based on its ID, within an item layer that contains multiple curves. When the value is set to -1, all curves will be probed. Curve are tagged generally in the order they are created, starting with the first curve at id 0.

Type: The 'Type' option controls how the curve is evaluated. The 'Fraction' option evaluates the curved based on its overall length producing a value as a fractional amount of that total. The 'Parameter' option will evaluate the curve based on the locations of the vertices that define it, for example a three point curve, the 50% position would be the middle most vertex, even if it was located near the first vertex that defines the curve.

Maximum Distance: The Maximum Distance defines are area around the curve for evaluation. If the distance from the point being evaluated is greater than the distance to the bounding box containing the curve plus (+) the maximum distance, then the evaluation for that curve is skipped.

Falloff Probe
The 'Falloff Probe' is a channel modifier that allows users to sample the value returned from a falloff, based on the sample position. Used in association with a 'Falloff', the probe is connected to the Falloffs graph connection on the node and and XYZ position to the appropriate Locator item channels. The Output channel returns a 0 to 1 value that is the falloff multiplied at that location.

Position X/Y/Z: Link the World Position transform channel of a 3D item or the Position transform output of another Channel Modifier item into this channel.

Output: This output represents the strength value of the falloff at the sampled location and can be connected to any single numeric value input channel.  Falloff Probe--

Position X/Y/Z: These Position values define the sampling point of the Falloff. Users can manually enter values to define the location in 3D space or connect the Position inputs of the node to the Position outputs of a Locator.

Output: The 'Output' value represents the sampled value form the Falloff, most often connected to the input of another node as a driver of the channel. Comments (3) funk April 26, 2014 at 2:47 PM

Matt Cox gives more details on the curve probe here:
http://community.thefoundry.co.uk/discussion/topic.aspx?mode=Post&f=3&t=87236&p=787424#787424

Sergio Mucino May 20, 2014 at 4:10 PM

There's a lot of channels on these probes that are not explained at all. Some information on them would be very useful.

Conor Fitzgerald June 11, 2014 at 2:19 PM

From Matt Cox in that post:

The curve probe takes an input position (matrix) and a curve. It looks for the closest position on that curve to the input position. It then returns info about the curve at the position on the curve that it's closest to.

Curve ID
The Curve ID channel specifies the curve that you want to search for the closest position. I believe this matches the polygon ID. Setting this to -1 will look at all curves on the mesh layer and find the one that the input position is closest to.

Maximum Distance
This specifies the maximum distance to search for a position on the curve. This can be useful if you want to improve speed of evaluation, as it will limit the search area (for the closest curve) to the maximum distance. When you're doing things like nodal shading with the curve probe, this can speed things up slightly.

Percentage
This is the percentage along the curve (with 0.0 being the first vertex and 1.0 being the last vertex) that is closest to the input position. This can either be a fraction of the curves length, or the parameter of the curve.

Distance
Distance is simply the distance in a straight line from the input position to the closest position on the curve.

Position
This is the position of the closest position on the curve.

Tangent
This is the tangent of the closest position on the curve. In other words, the direction the curve is moving, at the closest position to the input position.

Length
This is the overall length of the curve, regardless of the position being probed.

Top