Photomatch

Use it!

Used to calibrate a view camera such that the viewing perspective matches that of a photograph or rendered image. This lets you render a building or other objects over or into the image.

In order to use Photomatch, you must first:

• Use the Define Camera tool to set up a camera view that is approximately aligned with the image (see The Define Camera Tool). Generally, photographs are three point perspective, so you should set your camera view Projection to Three Point prior to matching the view to the photograph.

• Designate a number of “snappable” monument points in the model whose corresponding locations in the image are visible.

  Tool Setting	Effect
  Match	Updates the view camera based on the entered pairs of points. This button is disabled (dimmed) until sufficient pairs of points are entered.
  Clear	Discards previously entered pairs of points and prompts for entry of new pairs.
  Add	Prompts for entry of additional pairs of point.
  Adjust	Prompts for relocation of previously specified image points. See To refine the calibration by relocating previously specified image points.
  Lock Focal Length	Locks the focal length of the view camera so that it does not change during calibration of the view.
  Display Magnifier	If on, a magnified portion of the image is displayed (in the Photomatch settings window) to make it easier to enter an image point.
  Magnification	Sets the magnification factor for the magnified portion of the image.

To calibrate a view camera using an existing image

1. In the Rendering Tools tool box, select the Photomatch tool.


2. Select the view in which to calibrate the camera.

   The Select Photomatch Image dialog box, which opens if no raster image is visible in the view selected for photomatching.



3. Snap to a monument point in the model.


4. Accept the monument point.


5. Enter a data point at the image location that corresponds to the monument point.
   A handle is displayed at this location to identify the image point.


6. Repeat steps 3-5 to enter additional pairs of points, at least until the Match button becomes active.
   Specifying more pairs can improve the resulting calibration.


7. Click the Match button.
   The view camera updates.
   If the result is satisfactory, proceed with rendering or detailing the model. Otherwise, continue with step 8.
   If, when you click the Match button, an error message displays, enter more pairs of points and/or use view controls to refine the alignment of the model with the image. Then click the Match button again.


8. (Optional) To refine the calibration by entering additional pairs of points, click the Add button.
   or
   (Optional) Follow the procedure To refine the calibration by relocating previously specified image points.
   or
   (Optional) To discard all pairs of points, click the Clear button and return to step 3.



When using the standard view controls, you must turn off the Move Camera toggle to maintain the photomatch setup and the camera position.

To refine the calibration by relocating previously specified image points

1. In the Photomatch settings window, click the Adjust button.


2. Identify an image point to adjust by entering a data point on its handle.
   The handle is dynamically displayed.


3. Enter a data point to define a new location for the image point.


4. (Optional) Repeat steps 2-3 to relocate additional image points.


5. Click the Match button.



When entering a pair of points or relocating an image point, Resetting “backs up” through the entered points, removing previously entered points. This makes it easier to correct errors made while entering pairs of points.

Key-in: MATCH PHOTO

Photomatch works properly if you render the camera view. It may give incorrect results if you update a rendered view.

Photomatch relies on accurate photography for the background image. Its transformation is inherently linear and cannot compensate for the spherical distortions that are apparent in some wide-angle photographs.