Get y from a curve by given x

Revit
,
1

Greeting,

I want to generate a list of y values from a curve by give the x. This is what I have gotten. Is there a node to achieve it or a python script would help as well.

Thank you for the help.

2

If you meant to attach an image it did not show up. Try again and we’ll see where you’re at.

There are two basic ways to go about this:

  1. Mathematically, using the function that defines the curve. This would just be a case of actually solving for y. Super straight forward but assumes you have a mathematical function representing the plotted curve - which I’m guessing you don’t.
  2. Geometrically, relying on the geometry functions (and obviously math) to locate a point along the curve and return its coordinates. This is still pretty straight forward but gets a little fuzzy depending on whether you want your x and y coordinates in relative (curve) space or global space. Same consideration for orientation and alignment.

Assuming the start of your curve is (0,0), you can use Curve.PointAtParameter to get a point located on your curve at a specific parameter location. Keep in mind a parameter in this context is a relative value between 0 and 1, so you will have to do some arithmetic to move between global coordinates and relative parameter, but the result will be a point in space that you can pull coordinate values from.

DynamoSandbox_2025-12-11_10-42-42

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Alternately use plane intersects to get the Y value at X

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an alternative with scipy

Here is an example of interpolating a point from an abacus curve.

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import sys
import clr
clr.AddReference('ProtoGeometry')
import Autodesk.DesignScript.Geometry as DS
from Autodesk.DesignScript.Geometry import *

import scipy
from scipy.interpolate import interp1d
import numpy as np

curve = IN[0]
x_new = IN[1]

pts = [curve.PointAtParameter(i) for i in np.linspace(0, 1, 30)]
data = [[float(p.X), float(p.Y)] for p in pts]
x, y = [i for i in zip(*data)]

f_cubic = interp1d(x, y, kind='cubic', fill_value="extrapolate")
#
y_interpolate = f_cubic(x_new)

OUT = DS.Point.ByCoordinates(x_new, float(y_interpolate), 0)
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Using planes is a good way to work with the global axes without having to convert anything relative to the curve’s geometry. Nice.

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