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fig 1. By balancing Rotation and Attraction values, particles can flow down a curve while rotating. | fig 2. By mapping the speed, attraction and rotation speed with Ramp nodes, a vortex can easily be molded and shaped. |
The curve field uses a NURBS curve to generate dynamic force. Both Rigid Bodies and Particles can be effected by the field. Unlike the Curve Flow clip effect, the Curve Field is a true field, and as such, it exerts its force just like any other field, by adding it to the inputForce[] attribute of the dynamics object.
To create a Curve Field through the GUI, select at least one NURBS curve and then the menu item Fields -> Curve . This will create a Curve Field with the settings found in the Fields -> Curve -> Option Box window.
The following behaviors for field creation also apply :
For each NURBS curve in the selection, a Curve Field will be created.
If you have one or more particle objects selected when creating the fields, each particle object will connect to each new Curve Field automatically.
*The order in which you select NURBS curves and particles is NOT important.
To control the effect of the Curve Field on your particles, there are up to three controls for each attribute :
1. Basic Float Attribute - ex. "speed"
2. Mapped Attribute - ex. "speedMap"
You can assign a Ramp node to this attribute to enable you to modify the value of the attribute along the length of the curve. The values of the ramp are read from bottom to top, equating to start of curve, end of curve. It is recommended that you ensure your curve has a 0 - 1 U parameter range for best results.
If
this attribute is mapped, the resulting value will be multiplied by the Basic
Float Attribute (speed), so it is unnecessary and often confusing to use
the Color Gain attribute of the ramp as a global multiplier of the ramp value.
You can however use both positive and negative values for the entries in the
ramp.
*If this attribute does not have a ramp connected to it, it will be ignored.
3. PP Attribute - ex. "speedPP"
You can assign a custom float array attribute from your particle object to this attribute. This enables you to have per particle control of the value of the attribute.
Enter the name of the attribute from your particle object that you want to use to control the magnitude. If the attribute does not exist, the field will not evaluate. The field will read the values from the particle object each time it is evaluated and for each particle object connected to the field, so you could have several different particle objects connected to the field and for each one, if the attribute exists, it will be used.
If the attribute exists, it will be multiplied by the Basic Float Attribute and the Mapped Attribute (if it is mapped) to determine an overall value.
*When using a PP Attribute, it is important to remember that if you have a Runtime expression controlling the value of the attribute that the field is reading, if "Expressions After Dynamics" is turned ON for the particles, the values used will always be off by one frame since the field is evaluating before the expression.
Magnitude
Magnitude acts as a multiplier of the overall effect of the field.
MagnitudePP MagnitudePP enables you to have per particle control of the Magnitude of the field. The resulting value is NOT multiplied by the Magnitude attribute.
1. Evaluation of the field will not occur if :
the magnitude of the field is 0 and either the magnitudePP attribute has not been set or the specified attribute for the magnitudePP does not exist on the particle object.
2.
Deleting the curve that is connected to the field will result in the curve data
being baked into the field for the remainder of the Maya session. However, the
data will not be stored when the file is saved, resulting in the field not working
when the file is reopened.
Gaseous or Liquid Flows
Flow your particle systems or rigid bodies along curves to achieve maximum control over your simulation.
Motion Currents
By creating multiple Curve Fields, you can simulate different types of currents of motions.
Vortex
Using Attraction and Rotation, you have a large amount of control over the shape and motion of your vortex'.
P.
My particles don't follow the bends of my curve and increasing the attraction
just makes them stick to the curve.
S. Decrease the conserve attribute of your particles.
P.
My particles are bunching up at the end of the curve rather than continuing
to move outwards.
S. If you have attraction set on the field, once the particles
reach the end of the curve, they are all going to be attracted to the end point.
There are several ways to solve this problem. The simplest would be to
map the Attraction Map attribute with a ramp and make the ramp white right up
to the top and then make the tip of ramp black. This way the particles
can continue to use the speed and rotation values that you have set, but there
will be no attraction at the end of the curve.