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NVIDIA NCP-OUSD Exam - Topic 4 Question 6 Discussion
Topic #: 4
Another department at your company has provided layer1.usda that has a Sphere Gprim with animated timeValues that translate the sphere along the Y-axis:
#usda 1.0
(
endTimeCode = 60
startTimeCode = 1
)
def Xform "Asset"
{
def Sphere "Sphere"
{
double3 xformOp:translate.timeSamples = {
1: (0, 5.0, 0)
30: (0, -5.0, 0)
60: (0, 5.0, 0)
}
uniform token[] xformOpOrder = ["xformOp:translate"]
}
}
You've been given rootLayer.usda that references Sphere from layer1.usda as follows:
#usda 1.0
(
endTimeCode = 60
startTimeCode = 1
)
def Xform "World"
{
def Sphere "Sphere" (
prepend references = @./layer1.usda@
)
{
}
}
For testing purposes, you want to check what Sphere would look like if it was at (0, -5.0, 0) at timeCode = 45. Which of the following changes in rootLayer.usda would place Sphere at -5.0 in the Y-axis at timeCode 45? Note that it is okay if the position of Sphere at other timeCodes is changed. Choose two.
At timeCode 45, the referenced animation from layer1.usda interpolates between the samples at 30 and 60. Since the Y values are -5.0 at frame 30 and 5.0 at frame 60, the interpolated local translate at frame 45 is 0.0. Option A works because adding a parent transform on /World at frame 45 contributes an additional Y translation of -5.0; combined with the sphere's interpolated local value of 0.0, the resulting placement is Y = -5.0.
Option C also works because a layer offset retimes animation across a reference. NVIDIA defines a layer offset as an adjustment to time values when composing layers through references, payloads, or sublayers, using offset and scale to retime animated data non-destructively. With offset = 15, the source sample at frame 30 is composed at frame 45, so the referenced sphere evaluates to Y = -5.0 at root time 45. Value resolution accounts for layer offsets and interpolation of time samples.
Option B only changes timeline metadata and does not retime or override the animation. Option D interpolates between -2.5 at frame 30 and -5.0 at frame 60, producing -3.75 at frame 45, not -5.0. This aligns with Composition Reference, Layer Offsets, Time Samples, and Value Resolution.
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