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Topic: Biggest Synth Possible

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gavindjharper (Over 1 year ago)
Ok, here's a question... 

What is the biggest amount of data that I can input into a single photosynth... if I were to use all of my 20 GB allowance for a single synth, could I create one? Also what is the "photo density" required for successful synthing. I'm thinking of making a virtual model of a local visitors attraction that spans about 4 acres. I was thinking that I could spend a weekend there and try and shoot 20 Gigabytes of Pictures which on my 6.1 Megapixel camera equates to about 400 ish pictures per gigabyte... would this be sufficient? Any ideas? Can you join together smaller synths, i.e. do it in sections?

Also... if I were to synth smaller sections, then align the point cloud on a map; when I browsed the point cloud, would it automatically merge images from any adjacent points clouds? So many questions... any ideas!
Nathanael (Over 1 year ago)
Excellent question, Gavin,

I'm no one official, but I can point you to some pieces of data that I have collected over the past year.

> The maximum size of a synth cannot be measured in the number of megabytes constituted by the photos from which a synth will be derived.

> The synthing process is accomplished by matching image features (corners or blobs) across photos. 

> Although the full sized images are uploaded to Photosynth servers, all images, regardless of their full size, will only be scanned for image features at 1.5 or 2 megapixel detail level, so as to not cripple end users' machines with too many image features to match. 

> Because of this, the maximum resolution of any given image is not a constraint in the size of a Photosynth.

> Depending on what the subject of the photo is, the number of image features (the sort that the synther cares about) may vary wildly.

> Because of this, no hard number of images constitutes a maximum size of a synth.
Nathanael (Over 1 year ago)
> Photosynth examines texture to then match. This means that if you think in terms of covering individual surfaces, rather than whole objects, you will be thinking more like Photosynth does.

> In the 'Scene Reconstruction' phase, the more images of a single surface or single set of surfaces, the more detailed and likely accurate the pointcloud of that surface or surfaces will be.

> It is possible (I have only achieved this once) of taking so many photos of a single part of the scene that the number of image features which correspond to each other overwhelmed the synther during scene reconstruction, resulting in failure.

> The synther is a 32 bit program. This means that there is a finite amount of RAM which it is capable of utilising. Once this limit is breached by the number of image features and the amount of resources required to hold all of their positions in memory during scene reconstruction, your synth will fail.
Nathanael (Over 1 year ago)
> If constructing the largest synths possible is your goal, maximise Windows' virtual memory, have plenty of room on your hard disk which hosts Windows' 'Temp' folder, and have more than 2GB of RAM installed. I believe that the maximum amount of RAM which a 32 bit application can consume is 2GB. You should have more than this for constructing synths so that after your operating system and other running programs have consumed the amount of RAM which they need to run, you will have 2GB left over for the synther at all times.

> Understand that the largest collections may, in fact, be far more difficult to navigate. 

> Understand that the largest collections may degrade the quality of the reconstruction of any one part of a large widespread scene or collection of scenes.

Those are the main points on current synth size limits (other than mentioning that big dense pointclouds are really really cool =).
Nathanael (Over 1 year ago)
As to your question of synthing smaller chunks of the landscape and aligning them all to the map, you are ahead of the game.

Sadly today we can still only browse one geo-aligned synth at a time, even in the Bing Maps Beta ( http://bing.com/maps/explore/ ).

Rest assured that you are not asking for something which has never crossed the minds of the Photosynth team. The very reason that Photosynths are 'upload only' (well one of the reasons) is that as soon as possible, they may be linked together (and presumably browsed as one). For more details on this, please see the following link: ( http://getsatisfaction.com/livelabs/topics/linking_synths ).

For more information to aid in your own research, please see a small list of Photosynth related media which I have compiled here: ( http://cid-0ef7a30c1e7b926c.skydrive.live.com/browse.aspx/Photosynth :: Excel 2007 or 2010 neccesary for proper viewing ).
gavindjharper (Over 1 year ago)
Thanks Nathaniel!!! This is immensely helpful!

All the best,

Gavin
Insancipitory (Over 1 year ago)
I have about 4 years of Seahawks game photos about 2800 in total that I had been planning to combine into one massive synth.  Obviously, everyone knows why that didn't work.  Any thoughts on the best way to divide them into seperate synths?  Naturally, I have my own idea, but there's a pretty good chance someone else has a more interesting one.
Nathanael (Over 1 year ago)
Insancipitory, sorry to have not responded for so long. I'm not sure if you'll ever see this reply. Also if anyone out there has any better ideas, please let us know. 

A sports stadium seems like it will be a very difficult synth subject, simply for the reason that the crowd seems like it will dramatically change the appearance of the stadium, even through the length of one game as people continually move. Given that the field's markings stay the same over time, they may provide something for the synther to latch onto, but I honestly don't know.

I would simply try to divide the photos by section of the stadium that they're looking at and synth them in those groups. On a bright side, I've seen half your number (1400 photos) successfully synth many times, so you might be able to get away with two single groups, provided that the photos are close enough to each other.
michaeldenis (Over 1 year ago)
Good idea, Nathanael: split into groups by some logical idea (say area, night/day, game) and give it go.  I agree thagt these limits can be frustrating.  Good luck, nonetheless.

As a side issue, I wonder if someone could collect together those 1400+ photo synths.  I haven't seen so many myself, but then again I confess to being less of a viewer than I could be.  Actually, an overall statistical analysis of synth size and synthenis would be interesting to see.  How about it 6-member team photosynth?
Nathanael (Over 1 year ago)
@michaeldenis, 

Sorry to have not responded for so long. I actually started making a list back when you asked the question but just never got around to finishing it or posting it. I did post what I had found over at http://getsatisfaction.com/livelabs/topics/how_can_i_make_a_bigger_synth if you're interested.

I've also seen a couple of synths that are right around 2000 images, but the general rule is that they are comprised of extremely low quality images such as video frames or that the photos do not all belong to the same point cloud.

http://getsatisfaction.com/livelabs/topics/host_photos_at_own_server#reply_1949931
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