Incorrect Ternary Coordinate Validation in TriangularAxis.GetCoordinates #4797
Description
The current implementation of GetCoordinates in TriangularAxis incorrectly validates ternary coordinates. It enforces that leftFraction + rightFraction = 1, which violates the fundamental rule of ternary plots, where the sum of bottomFraction + leftFraction + rightFraction must always equal 1.
Current Problematic Code
public Coordinates GetCoordinates(double bottomFraction, double leftFraction, double rightFraction)
{
if (leftFraction + rightFraction != 1)
{
throw new ArgumentException("sum of left and right fractions must equal 1");
}
return GetCoordinates(bottomFraction, leftFraction);
}
Issues with this Code
1-Violates the ternary constraint:
- The correct ternary rule states that: bottomFraction+leftFraction+rightFraction=1
- The current check only ensures left + right = 1, which means bottomFraction can be anything, leading to invalid ternary coordinates.
2-Allows invalid values:
- Example input (0.5, 0.8, 0.2) results in 1.5 (invalid), but the current function does not catch this.
- Example input (0.5, 0.3, 0.2) is valid (sum = 1) but gets rejected because left + right != 1.
3-Does not support clockwise vs counterclockwise configurations:
- Ternary plots can be visualized clockwise or counterclockwise, but the existing function does not account for that.
Proposed Fix:
public Coordinates GetCoordinates(double bottomFraction, double leftFraction, double rightFraction)
{
if (Math.Abs(bottomFraction + leftFraction + rightFraction - 1) > 1e-6)
{
throw new ArgumentException("The sum of bottom, left, and right fractions must equal 1.");
}
double x, y;
if (!Clockwise)
{
// Counterclockwise transformation
x = 0.5 * (2 * bottomFraction + rightFraction);
y = (Math.Sqrt(3) / 2) * rightFraction;
}
else
{
// Clockwise transformation
x = 0.5 * (2 * rightFraction + leftFraction);
y = (Math.Sqrt(3) / 2) * leftFraction;
}
return new Coordinates(x, y);
}
ScottPlot 5.0.54