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Registered: ‎03-06-2013

Camera flipped backwards?

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06-21-2012 12:13 AM
Has anyone had this strange issue?

I have all my locators lined up and calibrated, but I notice a few of the cameras are flipped so that it looks like it's viewing from behind the image. I noticed this by placing what was supposed to be my reference geometry(cube) extruding properly in y direction in most of my images except a few where the +y becomes -y. I confirmed it further in Maya.

So now I have light poles(for example) that when modeled to some images will be on the complete opposite of certain images. (locators are where they're supposed to be on the images, it's just the camera views it from the back instead of the front!)

I've seen this on and off for a while and usually get around by just re-doing everything but this isn't always tenable due to size of some projects. My other solution was to mirror the offending cameras in Maya. This is fine so long as my project has nice corners to use for an xyz. The problem is that when I'm working on more organic shapes(like domes) that don't have corners to work from, trying to come up with a proper xyz when half the cameras are flipped backwards is a complete nightmare.
Any solutions?


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Registered: ‎08-19-2006

Re: Camera flipped backwards?

06-28-2012 01:43 PM in reply to: shutyermouth
First thing to check is to make sure you didn't reverse some markers. You don't have to start over to do this. If you have more than enough markers select half and right click and select don't use for calibration. This will put them in the list for locators used for modeling. Try recalibrating. If the problem persists, try the opposite selection.

The other times I have seen this is when you have cameras exactly 180 degrees from one another. IM doesn't like very exact relationships like this, it prefers a little staggering between images.
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Registered: ‎10-27-2012

Re: Camera flipped backwards?

04-01-2013 07:08 AM in reply to: shutyermouth
Of course my comment is too late, but still. If you use an undistorting mechanism embedded in "IM", then you should exactly know how it works. It can be unpredicted sometimes.
I got this situation a few times.
But lets say properly that there may be a few cameras in scene, and each of them may have a few shots (when more than one physical camera used). In my case I got the "flipping situation" with all the shots of one camera. Undistortion was automatic (that is when you select distortion type as "constant" or use option "all shots have the same zoom"). And "IM" automatically undistorted shots with inversed (or just incorrect) distortion value. If then select type as "known" and set a proper distortion value manually it fixes the problem. Sometimes a several manipulations with distortion parameters helps.
Also setting the principal point as "known : 0.5, 0.5" may improve tha quality of calibration (I think the Autodesk is reasonably to set this option as the default in IM).

IMHO theoretically if you use a small perspective between the shot markers (for example the shots of a small object from far distance with a huge zoom, when your projection is orthogonal-like) you may expect that flipping effect as normal. Because the program may interpret your locator positions in two different ways - straight and inversed.