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PostPosted: Tue Jan 28, 2014 1:38 am 
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Hi, i try to figure out question which Ransac model to use, when you shooting with 600mm lens on panoramic gear.
I would like to know it, because none of panoramic gear can not rotate around the nodal point 600 mm lens.
And in this case I am inclined to homography. Am i right ?

thx
Rasto


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PostPosted: Tue Jan 28, 2014 2:38 am 
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With a 600mm lens, the nodal point doesn't matter.
If you use the default values the stitching is perfect.

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Martin


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PostPosted: Tue Jan 28, 2014 11:03 am 
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lumelix wrote:
With a 600mm lens, the nodal point doesn't matter.
If you use the default values the stitching is perfect.



This is what the documentation tells:

"
Ransac model: Lets you to select the detection algorithm.
Similariy:
Homography:
"

Wow - soo informative . . =D :cool:

Klaus


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PostPosted: Wed Jan 29, 2014 12:11 am 
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Similarity - when the shot was made with pure rotation around the nodal point
Homography - when shooting is done from two different points of view

klausesser wrote:
lumelix wrote:
With a 600mm lens, the nodal point doesn't matter.
If you use the default values the stitching is perfect.



This is what the documentation tells:

"
Ransac model: Lets you to select the detection algorithm.
Similariy:
Homography:
"

Wow - soo informative . . =D :cool:

Klaus


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PostPosted: Wed Jan 29, 2014 3:13 am 
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does checking multiple viewpoints change it to use homography?

If I handhold the majority of my panoramas should I default to using homography?

What's the penalty to using homography on a perfectly nodal point rotated image?


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PostPosted: Wed Jan 29, 2014 9:54 am 
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foundation wrote:
does checking multiple viewpoints change it to use homography?

No, they are independently set options.

Quote:
If I handhold the majority of my panoramas should I default to using homography?

Don't know.

Quote:
What's the penalty to using homography on a perfectly nodal point rotated image?

Don't know.


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PostPosted: Mon Feb 03, 2014 6:39 pm 
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Hi,
lumelix is right, with a 600mm focal the similarity approximation is perfectly suited even in case of parallax.
Best regards.


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PostPosted: Tue Feb 04, 2014 5:33 pm 
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With a 600mm focal length, similarity is fine. Imagine you have a 600mm image of an object, a building facade looking straight. To be able to justify homography, it would mean that you need to change the shooting location so that the same building facade is now looking oblique. with an angle. That means you just moved perhaps 200 m or even more than that.
Homography is here to help to stitch surfaces that you see from different angles.


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PostPosted: Fri Feb 14, 2014 1:00 pm 
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AlexandreJ, thanks for your reply.


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