incomplete point cloud on new synth.

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  • Updated 10 years ago
I just created a new Synth of the college I teach at. it is a bit large with 430 pictures bout for some reason the point cloud only covers about 1/4 of the whole building. does anyone know what went wrong?
here is a link to it.
Photo of sarahsliefie


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  • disappointed.

Posted 10 years ago

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Photo of Nathanael Lawrence

Nathanael Lawrence

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Hello, friend,

By way of introduction, I am no one official, but I've been in the Photosynth community since three days after it launched, nearly exactly two years ago so have the advantage of having read and listened to a lot of pointers from the Photosynth team and our peers as well as a fair bit of personal experience.

Your particular subject for this synth is a challenging one (as far as getting a continuous reconstruction of all of the walls), simply because of all of the trees that are growing so close to the building. The tree trunks won't have any problems helping you reconstruct things as long as you take your time moving past them, but the leafy tops won't form any clear reconstruction and will obstruct the camera's view of the walls which may fracture different sides of the building into their own point clouds.

A failure of Photosynth to connect two shots together usually boils down to a few simple errors. Here are some of the most common:

:: One or more of the photos has a significant amount of blur (whether this is a camera focus problem, a camera motion problem, or anything else that would introduce blurriness).

(This wasn't much of a problem with your synth. Only one or two of your photos had any significant blur problem, but they simply didn't connect to others.)

:: The two closest shots of a common subject which didn't match each other are at such different distances that the object occupies more than double (or less than half) of the photo frame in one photo that it does in the other.

-- Solution: When walking toward or backing away from things, take enough photos that the scale of your subject doesn't more than double or half in percentage of the frame that it occupies.

:: The two closest shots of a common subject which didn't match each other are from too different an angle (even if they are from an identical distance).

-- Solution: Take smaller steps when walking around a subject.

I noticed that you used a fair bit of looking all around you from single points of view. I won't say that this doesn't work, because if these points of view are close enough together, it works as well as any other shooting method (see this synth for an example of the multi-panorama style executed very well).

For me personally it is easier for me to keep track of what I have shot and what I have yet to shoot by prioritising by specific parts of an environment (for example, a specific wall of a building or even a specific segment of a specific wall) and performing a full orbit around this part of the environment. Fair warning is that shooting an entire building in this fashion is definitely shooting more than you strictly need to shoot, but it is very difficult for this method to fail to connect to itself. The only downside to shooting in this manner (orbit everything and then take photos walking between the things which you have orbited) is that it may have so many connections that your computer runs out of memory from keeping track of all of the matches, but it works very well for smaller subjects.