Step 4 Create a new camera using the 35mm preset. With the camera layer selected, hit P to open the Position properties. Copy and paste the Position properties to the light and ‘Projected’ layers. Move the ‘Projected’ layer slightly forwards on the Z axis so that it sits in front the light, then set the material options so that Light Transmission is at 100% and Casts Shadows is set to Only. Turn off the visibility for the projected layer.
Step 5 Create a new white solid, make it 3D and apply the grid effect to it (Effect > Generate > Grid). This will help you align the layer to the perspective of the projected image. Rotate the solid on the Y axis and push the layer down to align with the ground in the photo. Extend the layer to cover the entire ground area.