I am using QUrl.fromLocalFile(absolute_file_path) to load the source, and while it does seem to load the source, when I check the status of the QMesh() object, it still reports '1: a source mesh hasn't been assigned a source yet', which I don't understand.

I am probably overlooking something simple, but I have been almost entirely unable to find any documentation for Qt3d in Python. Thank you for any help,

import sys
import os
from PySide6.QtCore import (Property, QObject, QPropertyAnimation, Signal, QUrl)
from PySide6.QtGui import (QGuiApplication, QMatrix4x4, QQuaternion, QVector3D)
from PySide6.Qt3DCore import (Qt3DCore)
from PySide6.Qt3DExtras import (Qt3DExtras)
from PySide6.Qt3DRender import (Qt3DRender)

import os
os.environ['QT3D_RENDERER'] = 'opengl'

class OrbitTransformController(QObject):
    def __init__(self, parent):
        super().__init__(parent)
        self._target = None
        self._matrix = QMatrix4x4()
        self._radius = 1
        self._angle = 0

    def setTarget(self, t):
        self._target = t

    def getTarget(self):
        return self._target

    def setRadius(self, radius):
        if self._radius != radius:
            self._radius = radius
            self.updateMatrix()
            self.radiusChanged.emit()

    def getRadius(self):
        return self._radius

    def setAngle(self, angle):
        if self._angle != angle:
            self._angle = angle
            self.updateMatrix()
            self.angleChanged.emit()

    def getAngle(self):
        return self._angle

    def updateMatrix(self):
        self._matrix.setToIdentity()
        self._matrix.rotate(self._angle, QVector3D(0, 1, 0))
        self._matrix.translate(self._radius, 0, 0)
        if self._target is not None:
            self._target.setMatrix(self._matrix)

    angleChanged = Signal()
    radiusChanged = Signal()
    angle = Property(float, getAngle, setAngle, notify=angleChanged)
    radius = Property(float, getRadius, setRadius, notify=radiusChanged)

class Window(Qt3DExtras.Qt3DWindow):
    def __init__(self):
        super().__init__()

        # Camera
        self.camera().lens().setPerspectiveProjection(45, 16 / 9, 0.1, 1000)
        self.camera().setPosition(QVector3D(0, 0, 40))
        self.camera().setViewCenter(QVector3D(0, 0, 0))

        # For camera controls
        self.createScene()
        self.camController = Qt3DExtras.QOrbitCameraController(self.rootEntity)
        self.camController.setLinearSpeed(50)
        self.camController.setLookSpeed(180)
        self.camController.setCamera(self.camera())

        self.setRootEntity(self.rootEntity)

    def createScene(self):
        # Root entity
        self.rootEntity = Qt3DCore.QEntity()

        # Material
        self.material = Qt3DExtras.QPhongMaterial(self.rootEntity)

        # STL model of plane
        self.stlEntity = Qt3DCore.QEntity(self.rootEntity)

        # Check if file exists
        file_path = '<absolute file path>'
        if not os.path.isfile(file_path):
            print(f"Error: File does not exist at {file_path}")

        self.stlMesh = Qt3DRender.QMesh()
        self.stlMesh.setSource(QUrl.fromLocalFile(file_path))

        print(self.stlMesh.status())
        print(self.stlMesh.source())

        self.stlTransform = Qt3DCore.QTransform()
        self.stlTransform.setScale3D(QVector3D(1.5, 1, 0.5))
        self.stlTransform.setRotation(QQuaternion.fromAxisAndAngle(QVector3D(1, 0, 0), 45))

        self.stlEntity.addComponent(self.stlMesh)
        self.stlEntity.addComponent(self.stlTransform)
        self.stlEntity.addComponent(self.material)

if __name__ == '__main__':
    app = QGuiApplication(sys.argv)
    view = Window()
    view.show()
    sys.exit(app.exec())