new: project_ortho

__init__.py

@@ -1,3 +1,3 @@
-from .compute import matmul, rot_2D, rot_3D, transpose
+from .compute import matmul, project_ortho, rot_2D, rot_3D, transpose
 
-__all__ = ["matmul", "rot_2D", "rot_3D", "transpose"]
+__all__ = ["matmul", "project_ortho", "rot_2D", "rot_3D", "transpose"]

compute.py

@@ -95,6 +95,24 @@ def rot_3D(angle: float, axis: str) -> list[list[float]]:
     raise ValueError("axis must be 'x', 'y', or 'z'")
 
 
+def project_ortho(
+    point: tuple[float, float, float], scale: float = 1
+) -> tuple[float, float]:
+    """Project a 3D point onto the xy-plane and apply a scale factor.
+
+    The z-coordinate is ignored. The returned x- and y-coordinates are each
+    multiplied by ``scale``.
+
+    Args:
+        point: The 3D point as an (x, y, z) tuple.
+        scale: The scale factor to apply to x and y.
+
+    Returns:
+        The scaled 2D point as an (x, y) tuple.
+    """
+    return point[0] * scale, point[1] * scale
+
+
 def _validate_matrix(matrix: list[list[float]], name: str) -> None:
     """Raise ValueError unless matrix is non-empty and rectangular."""
     if not matrix: