QT - Draw a point at a user specified location in a 3D surface

I was going through the Surface example here

When the user clicks anywhere it draws a point

image surface

what i'd like to know is how to do this programatically,like, if a user gives 3 coordinates x, y, and z. How do I go about plotting such point?

you can add a custom item like so:

  QImage color = QImage(2, 2, QImage::Format_RGB32);
        color.fill(Qt::cyan);

        QVector3D positionOne = QVector3D(2.0f, 2.0f, 0.0f);
        QCustom3DItem* item = new QCustom3DItem(":/items/monkey.obj", positionOne,
            QVector3D(0.0f, 0.0f, 0.0f),
            QQuaternion::fromAxisAndAngle(0.0f, 0.0f, 0.0f, 45.0f),
            color);
        item->setScaling(QVector3D(0.1f, 0.1f, 0.1f));
        m_graph->addCustomItem(item);

Note that the .obj file must be a mesh file, you can generate one with blender for example, just don't forget to triangulate the mesh before you export the .obj file.