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Output parameters

Output Image Parameters Dialogue Box

This icon, F4 or the Tools->Output Image Parameters menu item will bring up the following dialogue box:

It is divided into 4 sections

  1. Scaling Factor
  2. : which adjusts the size of the rectified image.
  3. Mirroring
  4. : which allows the vertical and horizontal mirroring of the rectified image
  5. Rotation
  6. : which allows the rotation of of the rectified image
  7. Camera Distortion Parameters
  8. : which allows you to select which camera parameters to use for the rectification

Scaling Factor

The first area of this dialogue box deals with the scale of the output image. The first box is read- only and indicates the natural scale factor which is calculated from the size of the image and the distribution of your measured points. This value is not significant, we just need a starting point. The scale is in pixels per real world unit.

The "natural" value will be offered as the default when you first rectify an image but the final scale of the rectified image can (and should) be specified in the second box in this area. Ways to use this feature are as follows:

  1. If, at the natural scaling factor, rectification crops part of the image you want to retain
  2. decrease this value. Try rectifying the wall sample at its natural scale factor for an example of this problem.

  3. If, at the natural scaling factor, there is a lot of image in which you are not interested you can
  4. increase it. The cube sample at its natural scale factor is an example.

  5. If you want a printed image at a particular scale you can use this value to get it. It will take
  6. some experimentation with your printer to get this right but once set up it should work for all images rectified to that scale. A future release of ASR will try to simplify this procedure but for now, a rectified image that has 30 pixels per inch printed at 300 DPI should provide some sort of useful result. *
See Printing for other options.


Mirroring

The second area of this dialogue box has check boxes which will cause the image to be mirrored along either the horizontal or Vertical axises. The usefulness of this feature is less obvious (we put it in for debugging) but it has it's applications. For instance a stained glass window that you photographed from inside (because it shows better) but measured from the exterior (using mullion intersections perhaps) can be integrated into the exterior elevation by rectifying it to the exterior measurements and mirroring in horizontally.

Note: Do not use this option when rectifying for insertion into AutoCAD.


Rotate Image

The third section of this dialogue allows for the rotation of the rectified image. This is unlikely to be of much use in the case of 2D coordinate systems but can be very helpful when working in 3D.

Imagine, in the example below it was impossible fo measure the bottom right corner of the cube. (Usually there will be a shrub or a bus in front of important points)

So you measure the closest thing you can see but this will result in a somewhat rotated right face due to the fact that the O & H points are not parallel to the base plane.

The rotation tool can be used to overcome a missed measurement point in a couple of ways:

In the latter case precision may be difficult to achieve but you can get pretty close by using the Baseline command in the Rectified Image Window (available by holding down Ctrl ) or right clicking and selecting the Baseline option then drawing a line that will define the rotation of subsequent rectifications.

The wall sample is a real world example of the same problem except here there are no points on any axis.

Using the default O=1 H=2 V=3 you will have to rectify using:

  • horizontal mirroring
  • a rotation angle of 273.75 degrees.

  • Using O=1 H=4 V=2 you can rectify using:
  • a rotation angle of 4.75 degrees.
  • no mirroring

  • In both cases you will need a scaling factor of 35 or less to see the peak of the gable

    In these cases of inexact rotation angles you can get a pretty good idea of the quality of the result by selecting a vertical or horizontal line, zooming in and scrolling your reference line towards an edge to see if they are parallel.

    Note: Do not use this option when rectifying for insertion into AutoCAD.


    Camera Distortion Parameters

    The final section of the Output Parameters dialogue box deals with the camera distortion parameters you want to use.

    The first time you rectify an image the Take from camera descriptor button will be selected and the camera currently defined as the default in the Camera management dialogue box.

    If you are revisiting an image you have previously saved the Take from current PTS file option will be selected and the name of the camera used the last time the project was saved will be shown to the right. If there is a camera specified in the PTS file (including the camera "None") those parameters will be used for the next rectification unless you change it.



    * Sorry about the inches. ASRix does NOT support any sort of imperialism but especially not measurements it's just that the only printer information I have on this side of the ocean(s) uses this quaint terminology.


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    Inquiries to: steve@icomos.org

    Generated by: CART
    (Thu Sep 20 17:56:48 2007 )