Step 3: Aligning Photos

Now that PhotoScan knows which pictures you want it to work with, it is time to line them up spatially in relation to each other. Fortunately, the program does all the work here.

Once again, go to your “Workflow” menu and this time select “Align Photos.” A window will pop up (pictured below) with some settings to play with. If you want a really thorough explanation for what each does I recommend checking out: http://www.agisoft.com/forum/index.php?topic=3559.0.

align-photos-windowIn a nutshell though:

  • “Accuracy” is exactly what it sounds like. Higher will get you better results, but at the cost of a longer processing time and a model that is more taxing on your computer. I use “Medium” or “High” as the “Highest” setting takes a very long time on my computer and I am not sure it makes that big of a difference.
  • “Pair Preselection” is set to “Disabled” by default. Change this option to “Generic” to greatly speed up the processing time.

If you click on the “Advanced” tab you will get several more options.

  • “Key Point Limit” describes the maximum number of points the program will try to draw from a photo. A higher setting will improve camera alignment and increase processing times. The default is 40,000 and the post above was unable to see a difference with anything above that point. Because I have trouble with the idea of letting go of accuracy, I keep this set at 1,000,000.
  • “Tie Point Limit” sets how many of these points the program will use to align the photos to decrease processing time. If you set this to 10,000 the program will only use the ten thousand best points from whatever you set the “Key Point Limit” to. To use all the points, set this to “0.” If you feel that the photos are taking too long to align, then it might be worth adjusting this setting.
  • “Constrain Features by Mask” is a setting you will probably only need if you used a turntable for your pictures and have applied a mask to your photos. Leave this unchecked otherwise.
  • “Adaptive Model Fitting” improves your camera alignment in ways I do not understand. Leave this checked.

Once everything is set, hit “Okay” and let PhotoScan do its thing. Depending on your settings and how many pictures it has to process, this could take anywhere from a few minutes to hours.

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