Automated assistance with Tie Point picking

This feature is one of the core tools of image orientation yet many people do not
realise it exists. It can significantly improve the residuals of the orientation
calculation and also speed up the workflow. To use:

1. Assuming you have your two images of a pair open in the orientation screen, open
the "Pick Tie Point" tool either by right clicking on an image, or from the Orientation
menubar item.

2. Use the zoom tool to display the same area of the left and right images where the tie
point feature exists (remember to choose high contrast or strongly textured
features).

3. Accurately left click on the feature in the left image that you wish to use as the tie
point.

4. Enable the "auto correlation" tool to find the corresponding point via the clever
pixel-matching algorithm by clicking the centre scroll wheel of your mouse.
Alternatively, the auto correlator can be activated by clicking the "binocular" icon on
the toolbar (circled below).

5. A progress box appears which should quickly finish resulting in the control point
being detected in the right image automatically. Note - if progress bar
"hangs" on 70-80% for a long time, it is likely that it will not find a match so click
cancel and try another target.

7. If you are happy that I.M. has picked the correct feature, click "Measure" to register
the tie point.



ADVANCED TIP:



The above process will work on up to FOUR images at once. This can greatly speed up
picking tie points to link adjacent pairs of images (shown above).

- Holding down the control button, click on the four images you wish to open e.g. left
and right of the first pair and left and right of the next pair. Right click the mouse
and select "open images"



Repeat the steps 1-6 above. If successful, the tie points should be coloured YELLOW
indicating that they are common between two stereo pairs. Note that the minimum number of
points required to tie adjacent image pairs is 3.

NOTES:

- The auto correlation process only works on the visible parts of each photograph in the
zoomed in viewport. It will not work if you have different parts of the image in the zoom
viewport.

- If the subject being modeled has a repeated pattern (red bricks are a classic), the
correlator can sometimes fail by picking the wrong point, so always double check before
clicking "measure".

- If you have chosen good features to use as tie points (high contrast, unique etc.), the
auto-correlation process should only take a few seconds. If it hangs on >70% for more
than around 10 seconds it will probably fail, so click cancel and try again with another
tie point.

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