Use the 'PROJECTIVE_TRANSFORMATION' plugin to perform a linear transformation of a surface in one of the three orthogonal planes.

Click the menu icon to enable this plugin.

After the plugin is enabled, select the required orthogonal projection view tab. Then click on a control point of the surface to be transformed.

A selection box is displayed around the surface with magenta vertices.

Click on one of the selection box rectangle vertices and drag the mouse to transform the control points.

Release the mouse to complete the linear transformation. Repeat as necessary.

Click the menu item to disable the plugin mode.

This plugin is undo-able, but the undoing feature only works if you click away from the surface after the stretch. Don't disable the Plugin by using the GUI button!

For the dedicated staff at Hammersmith Hospital.