Forum : Photosynth Lounge

Photogrammetric, Oblique Image Stitching, Pets Dressed in Clothes Photos… this is a place to chat and share stories with your fellow Photosynthers. Not all topics have to be about photography, this is a place to relax and chat about whatever you fancy.


Topic: This is MADDENING

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chris.alexander (Over 1 year ago)
I have re-synthed the exact same photos 4 times and have gone from 41% to 39% to 36% - what is going on? The photos are overlapped by a minimum of 40%, no shiny surfaces, glass, water, etc. Why won't this thing stitch right?!?
Nathanael (Over 1 year ago)
Hi, Chris,

It's awfully hard to tell you why Photosynth is having problems with your photos when we can't see the synths.

Synthing is not a problem that has one single "correct" answer and depending on which pair of photos Photosynth begins solving the synth with, it may be able to solve it to a greater or lesser degree of satisfaction.

For more information, please read these two topics: 
http://getsatisfaction.com/livelabs/topics/two_synths_with_different_results
http://photosynth.net/discussion.aspx?cat=a6bad539-de7d-4a16-8c4d-b143f7d5f984&dis=38772776-3f6f-4f5e-b34a-0e9771d6f10e

Bear in mind that the synthy percentage is mainly just a measure of how many photos Photosynth was able to fit into the same cluster. Occasionally when the same group of photos is resynthed, the version with higher synthy percentage may actually make incorrect conclusions about how some of the smaller clusters connect.
Nathanael (Over 1 year ago)
Learning to shoot photos for Photosynth is a fundamentally different way of photographing a scene that does take some time to learn, but once you figure it out, it's not too difficult to get what you want from it.

Be patient and you'll find that you can pull of some pretty amazing things.

Don't be afraid to let the rest of us see some of your early synths. None of us were pros when we started and we've all got more to learn. Let us take a look and maybe you'll get some good pointers.

All the best!
Your fellow synther, N.
Nathanael (Over 1 year ago)
...pull *off* some pretty amazing things...
chris.alexander (Over 1 year ago)
Through re-shots, some image editing and trial and error I managed to get my % up to 59%. The system still seems to not be stitching together images with more then enough overlap, but it is better then before. Take a look :http://photosynth.net/view.aspx?cid=f11e6d41-80c3-4242-8c20-5b0f672fe6e0
Nathanael.Lawrence (Over 1 year ago)
Hi Chris, I don't know if you'll get this reply or not, but I wanted to make sure that someone wrote back to you.

Unfortunately you have chosen a subject that in many ways is not very synthy - namely, the hallways of the library. The walls, except for a few ornaments (which you largely rush past), are largely textureless and the grain of the carpet is too low resolution in your shots for the synther to track it. This goes for the ceiling tiles as well.

The bookshelves (or rather the array of books in them), on the other hand, and the marble stands that the sculptures stand on are things that the synther will love. If you can, try shooting along and around several bookshelves sometime and you should see much greater success.
Nathanael.Lawrence (Over 1 year ago)
Before I go much further, I should tell you where to download the Photosynth Photography Guide, especially as you work at a library. Get it here: http://photosynth.net/help.aspx I see that you list some of the things to avoid above, but thought that you may have only seen the 'How To Synth' video tutorial with Laura Foy.

You may also be provoked to think differently about your coverage by reading what I wrote in these discussions:

http://photosynth.net/discussion.aspx?cat=ceca0f30-0f7c-4468-811a-32b623ea8563&dis=d640bf96-4f5a-4944-9b20-756a2c0db725

http://photosynth.net/discussion.aspx?cat=ceca0f30-0f7c-4468-811a-32b623ea8563&dis=eb43040a-d959-4e2a-85b8-4936fcdbf659

Specifically addressing your above synth, for one thing, you do really well at the end of each hallway, because they appear in so many of the shots walking down the hall, but the middle of the hallways, you really rush past, without giving the synther a chance to learn anything along the way.
Nathanael.Lawrence (Over 1 year ago)
If I were to fly into Denver and try my hand at your hallways, I think I would do a simple orbit of especially synthy things (photos on the walls as one example) and then always use them as beginning or ending points for my paths.

This is to say, every time I had to move down a hallway, I would have begun by looking at something which I had just described to Photosynth by circling it and take photos which look from that object and then swivel over to look directly at the next landmark/synthable object/ and then be sure that you target it all the way over to it. Again, you did the targeting the end of the hallway very well, but you didn't fully define the scene once you got there, nor did you specifically define 'this is where I came from'.
Nathanael.Lawrence (Over 1 year ago)
The other tip for the library that I would give you (besides always thinking about tracking something while you move) is just to think about taking smaller steps. Again (through no fault of your own) the bare hallways are simply not things that Photosynth tracks well, so the more overlap the better.

You said above that you had given enough overlap, but I would point to things like going in, around, and out of the Gottesfeld room as clear examples of *not* having enough overlap. The huge steps that you took when you moved around the table in there are a very typical novice mistake. Don't be angry. It is a mistake that I made a fair number of times before I finally realized what sort of shooting I was going to have to do in order for Photosynth to not go astray.
Nathanael.Lawrence (Over 1 year ago)
Critical takeaway concepts from the guide include: 

"The Rule of 3" 
(This means a *minimum* of three photos of any given thing from different angles. If you expect to see the object in the pointcloud, apply this to individual surfaces, NOT *only* whole objects.)

"Limit the angles between photos."
(This goes back to "Take small steps.". Basically, don't expect Photosynth to recognize the same thing twice if you were standing more than 25 degrees away in the second photo from the place that you were standing when you took the first.)

"Avoid drastic angle and scale changes – a close-up of a sign may not stitch in if the only other photo of it is 100 feet away."

Lastly, again, it isn't your fault that the hallways are unsynthy. An expert photosynther would definitely have a tough time with it. Try making a synth where you walk in a full circle around each of those pedestals and sculptures individually and then once as a group and see how that works.
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