View iOS6 Panoramas on Photosynth

I was just trying out the new panorama feature built in to iOS6 (available on the iPhone 4S and 5).  The resulting panoramas look great, but one thing that I miss compared with Photosynth is the ability to view the result as a true “surround” experience. I was curious if I could work out the geometry of the iOS panoramas so that they could be uploaded to http://photosynth.net, and then be available to view anywhere–on the web or in the Photosynth App.

The quick answer is yes.  You need to get the Photosynth Export Plug-in for Photoshop. When you run the plug-in, select “Cylindrical (Horizontal)” from the “Projection” menu, and determine the “Field of View” of your panorama by taking the width of the image and dividing it by the magic number 53.5.

Here are two panoramas that I uploaded using this technique: Seattle 12th Street Bridge and Seattle Yesler Bridge.  If any readers try this out, please send us a link to the result via the comments or on Twitter.

That’s it.  But, if you want to know where 53.5 comes from, continue reading.

The figure below shows the iPhone sweeping out a panorama. I’m assuming that iOS reads the pixels from the camera and “projects” them onto a cylinder in order to form the panorama.  The cylinder is represented as the blue path in the figure. The length of this path is equivalent to the width in pixels of the panorama that was captured.

FOV

What the plug-in needs is the field of view (FOV) in degrees. From geometry we know that 

width = FOV  * radius

What is the radius in this case?  It is simply the focal length of the camera. Searching the web, we find that the 4S has a focal length of 4.28mm. Now we have a problem of units; we know the focal length in millimeters and the width in pixels. To convert between these units we can find out that the 4S sensor size is 3.42mm wide or 2448 pixels wide. Now we have our conversion; the radius in pixels is

radius = (2448/3.42) *4.28 = 3064 pixels

Finally

FOV = (width / 3064) * (180/p) = width/53.5

I haven’t yet found the sensor size and focal length of the iPhone 5, so 53.5 may not be the right number for that phone. Post a comment if you know.  I also think that a very similar calculation could be done for the Sony cameras with the sweep panorama feature.

-Matt Uyttendaele

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One Response to View iOS6 Panoramas on Photosynth

  1. Hi Matt,
    Sorry for using this unconventional way to get in contact with you
    I am Chris HEPP and I am working with APDER (Aerial Photos in Disasters Emergencies and Recovery) http://www.apder.org. We are a NGO (Non profit) and so far the only NGO dealing with this topic. We made last February a Pilot in Haiti and placed some results on the photosynth web site.

    Link: http://photosynth.net/userprofilepage.aspx?user=APDER&content=Synths

    We believe that ICE and Photosynth could be a good platform (new way) in dealing with catastrophes, natural disasters and emergencies.
    Therefore I would like to get in contact with some you or somebody of your team – if there is some interest from your side?

    I am also invited to a Conference in France
    Link: http://www.cartong.org/geong/2012
    to speak on the round table and to do a workshop which I intend to do with ICE and Photosynth.

    Consequently I might need some advice in the preparation for the workshop. I would be very great full if you can send me a contact telephone (preferable Skype since we are a volunteers organisation).

    kind regards from Barcelona

    Chris

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