objects, noticeable markings, etc. You also will want to spread the points out to
include different parts of the image. Depending on the complexity of the image,
you could need as few as 5 points. However, to get details in different parts of
the image to correspond, you might need to add additional points after you see
the results of the alignment (described below).
To save the points you’ve selected, save the scene file since they are simply another type of
annotation.
If you have accidentally produced pairs that are not matched up you can specify which points
are to be paired. Select one point,
Ctrl
-
Shift
, and select the corresponding point. They will
become a pair. If you have an unpaired point you can either delete it, or select it and the next
point you pick (in the other window) will be paired with it.
2:Calc
Once you’ve got correspondence points selected, the
2:Calc
button will become enabled. Select
this button to calculate the alignment of the color data to the range data based on your
correspondence points. When the calculation is complete you will see a popup window with a
number representing the quality of the fit – based on the ‘RMS’ (root mean square) error in
pixels. Numbers less than 3 are fantastic. Numbers between 3 and 8 are good. Anything larger
means you probably need to move some points or choose some others.
Note: With 2k x 3k pixel images (the DeltaSphere camera’s standard), and scans
of 13.33 samples per degree (also standard), 3 pixels is approximately equal to 1
range sample.
If you end up with a very large error number, perhaps 30, you will probably find that you’ve got
a pair of points that were not supposed to be matched and you’ll want to fix or delete them.
Regardless of the number, you won’t be sure of the quality of the alignment until you get to step
4 below.
3:Apply
If you’re satisfied with the results of step 2, the next step is the
3:Apply
button which is now
enabled. This function applies the alignment to the image making it an ‘aligned’ photo. It also
displays the pairs of correspondence points in each window so you can judge how close the fit
was. If you like, you can select and move correspondence points using the arrow button – but
only in the window in which they were created. You can then choose Calc and Apply again.
Apply doesn’t actually change the image data at all; it merely associates an alignment with this
photo in the scene file. Once a photo is aligned like this, you can use the measurement tools
directly on the image data and get accurate results.
If you would like to undo the Apply function and add to or edit the points, go to the Edit menu
and choose
Align
->
Clear Alignment
. You can also edit the points and choose Calc and Apply
to simply overwrite the previous alignment.
DeltaSphere-3000 3D Scene Digitizer
81
9/23/05
