3D Compositing with Action >

# Perspective Grid

Use the Perspective Grid node to help you with perspective alignments in your Action scene. The perspective grid creates a rectangle on a plane within the perspective of the clip. The accuracy of the plane determines whether any adjustments are properly scaled and oriented in your clip. Objects can be placed anywhere on this plane. Aligning objects to the perspective grid has multiple benefits:

- You can perform a 4-corner pin with a surface or geometry that respects the perspective.
- Aligning the grid establishes the orientation of the plane in 3D space and the Field of View (FOV) of the camera that shot the scene.
- Because the Perspective Grid node has an axis-like behaviour, objects attached to it inherit the grid's 3D transformations.

To align an object with a perspective grid:

1. Click Media.
2. In the Media menu, select the media you want to use for the perspective grid (you can change the media later in the Perspective Grid menu).

   This media becomes the reference for the perspective grid alignment.

3. Do one of the following:
   - Drag the Perspective Grid node from the node bin and place it in the schematic.
   - Drag the Perspective Grid node from the node bin and place it where you want it in Result view.
   - Double-click the Perspective Grid node. You do not need to be in Schematic view to add a node in this manner.

   The Perspective Grid object is added to the schematic. In the Schematic view, the number in brackets next to the name of the node indicates the media used for the perspective grid reference.

   To specify different perspective grid reference media, select the media in the Media menu, then click Apply, or enter a different media number in the Use Media field of the Perspective Grid menu.

4. With the Perspective Grid object selected in the schematic, select Object view from the View box (or press F8) to see the grid and the selected media.
5. While in Object view, drag each of the four corners of the rectangle to the desired location. The grid automatically aligns to the new perspective.
   NoteWhen dragging one of the corner points of the rectangle, if your desired location cannot be computed (for example, if a point goes past another point on the plane), the location is remembered with a dotted line and red circle. Once you move other corners, your original location may now become viable, and the rectangle and grid align properly.

   - If Allow Adjustments is selected in the Lock Camera box , the target camera FOV and position adjusts to fit the perspective set by the perspective grid. If Lock Camera is selected in the Lock Camera box, the perspective grid does not adjust the target camera.
6. Once you are satisfied with the alignment of the perspective grid rectangle, parent an object to the Perspective Grid node. The object inherits the perspective transformation of the Perspective Grid node. Switch to Result view (F4) to see the complete scene.
   NoteYou can also manipulate the perspective grid in the Result view, provided that Lock Camera is not enabled in the Perspective Grid menu, or the perspective grid camera is the same as the Result camera.

Perspective Grid Menu Reference

Use the settings in the Perspective Grid menu to help you perform your alignment.

Lock Camera box
  Select Allow Adjustments to allow adjustments of the Target camera FOV and position. Select Lock Camera to lock camera FOV and position.

Perspective Camera box
  Specify which camera to view the perspective grid in Object view, and for modifying its FOV when working with the perspective grid.

Perspective Camera field
  Displays the active perspective camera number. Non-editable.

Stereo Camera Perspective box
  Select whether to use the left or right camera from a stereo camera rig when working with the perspective grid.

FOV field
  Displays the field of view of the active perspective camera. When adjusting the perspective grid, the FOV of the target camera updates automatically (unless Lock Camera is enabled). Non-editable.

Width field
  Displays the width of the four-point perspective grid rectangle. Non-editable.

Height field
  Displays the height of the four-point perspective grid rectangle. Non-editable.

Lock Size button
  Enable to lock the width and height of the perspective grid rectangle. For example, use to lock the dimensions of the grid when animating it, if the feature size you aimed for in the image doesn't change in time.

Use Media field
  Displays the number of the media associated with the perspective grid. You can change the media number in this field, or select a media entry in the Media List and click Apply.

Z Offset field
  Displays the amount of offset to apply along the Z axis to make the grid larger or smaller while maintaining the visual result.

Display Grid button
  Enable to display the grid lines in Result or Object view.

Grid Colour pot
  Displays the colour of the grid lines. Click to change the colour.

Magnifier button
  Enable to display the magnifier while dragging a corner of the perspective grid rectangle in Object view.

Zoom field
  Displays the zoom factor of the magnifier. Editable up to 5x.

Reset button
  Resets the perspective grid settings, but does not reset the active perspective camera settings.

Working with FOV

You can animate the perspective grid by positioning corner points in other frames. To create an animated transform, place the grid in the first frame, then Lock Camera in other key frames. You would also enable the Lock Camera if the camera FOV does not change over the clip.

NoteIf you enable Allow Adjustments, Action will solve for the FOV in each frame on which you edit the corners.

To use the existing value in the camera and not solve for it, regardless if you animate the perspective grid, you should lock Camera before positioning in the first frame.

NoteWhen the FOV of the camera is computed (not locked) the camera is repositioned in order to frame the media.