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Author Topic: Stitched Panoramics - Straight Horizon Possible?  (Read 3262 times)

Murray Fredericks

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Stitched Panoramics - Straight Horizon Possible?
« on: March 15, 2008, 03:24:31 am »

Hi All,

is it possible to achieve a perfectly straight horizon stitching panoramics beyond where I would normally use 'shift' to ensure there was no bending.

Basically I will have to use a 'cylindrical' projection as a perspective stitch will not work that far around.

I am using Alpa lenses and rollei lenses and MFDB.

Cheers

Murray
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Thomas Krüger

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Stitched Panoramics - Straight Horizon Possible?
« Reply #1 on: March 15, 2008, 05:13:30 am »

Tutorial for PTGui: http://www.dffe.at/panotools/ptgui5-03e.html

Autopano Pro does a good automatic job leveling the horizon.
Video: http://www.autopano.net/wiki/action/view/H...hten_a_panorama
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Panopeeper

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Stitched Panoramics - Straight Horizon Possible?
« Reply #2 on: March 15, 2008, 11:03:21 am »

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is it possible to achieve a perfectly straight horizon stitching panoramics beyond where I would normally use 'shift' to ensure there was no bending.

First of all, you need to understand, that "horizon" in panoramic stitching is a concept, not a line and has not much to do with the conventional understanding of "horizon", which is very seldomly useful.

In cylindrical projection, "horizon" is the horizontal center line of symmetricity, This is straight per definition. It is your task, to define, what part of the image has to be on this line, i.e. what should appear as horizontal and straight.

Vertical lines appear vertical in cylindrical projection - if the stitching is correct. *All other* lines will be warped, and that has to be so. In other words: only one horizontal line will be straight and horizontal.

See this tutorian on horizontals and verticals and this tutorial on warping.

Only Panorama Tools based stitchers will do this right in all circumstances: Panorama Tools Assembler, Hugin and PTGui.
« Last Edit: March 15, 2008, 11:49:19 am by Panopeeper »
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roskav

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Stitched Panoramics - Straight Horizon Possible?
« Reply #3 on: March 15, 2008, 11:11:42 am »

I just spent a day doing high res MFDB cylindrical panoramas from the top of a building using realviz and photoshop ... Autopano by the looks of it would have been really useful to me (The client would have preferred planar) .. I wish I had known about it ...

Which stitching programmes do people rate here? .. I find Photoshop pretty predictable and good with large files .. but realviz of course is great for QTVRs .. Does Autopano rate well for Cylindrical / Planar conversions?

Ros

BTW for me the negative points of Image merge in PS are that it throws up some odd conjunctions in form but is very good for tonal blending.  ... and realviz presents a very odd Neuromancer view of the world when it doesn't get things right .. such as bendy buildings and complete meltdowns of form if the base info isn't there.
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Dustbak

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Stitched Panoramics - Straight Horizon Possible?
« Reply #4 on: March 15, 2008, 03:03:23 pm »

I always liked PTGui. Nowadays with my RRS pano package it has become very easy to do pano's. (have not started doing multirow yet).

I try PS first, if that doesn't get it right I go over to PTGui but PS is doing a great job in 99% of all cases. Trick is to really rotate around the optical axis (also sometimes called nodal point).

Hasselblad was kind enough to mention the place of the nodal point on its lenses making it very easy to find

I only wish RRS would have started the scaling the other way around and start with 0 on the side of the camera on their sliding bracket.
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Murray Fredericks

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Stitched Panoramics - Straight Horizon Possible?
« Reply #5 on: March 15, 2008, 07:47:56 pm »

Quote from: Panopeeper,Mar 16 2008, 02:03 AM
*All other* lines will be warped, and that has to be so. In other words: only one horizontal line will be straight and horizontal.



My question is then, if I stood on a cliff and shot the horizon over the ocean 180deg, could 'the' horizon be designated as the horizontal line to be straight?

I will obviously test this soon but it's good to know where I'm going...


I stitch regularly in PS and occasional PTGUI, but this particular challenge is new to me.

The Auto Pano Pro tutorial was great!

Murray
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Panopeeper

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Stitched Panoramics - Straight Horizon Possible?
« Reply #6 on: March 15, 2008, 08:31:09 pm »

Quote
if I stood on a cliff and shot the horizon over the ocean 180deg, could 'the' horizon be designated as the horizontal line to be straight?

It could, because the actual horizon is usually far away and your position is not really far above (and if you are hugh above, then the horizon is farther away).

Btw, you can cheat to some degree, *if* there are no clear verticals in the frames. Trees usually do not cause any trouble, but with cityscapes you don't have much freedom, see the tutorial I linked above. On the other hand, if there are clean vertical lines, it's enough to declare those (at least two) as verticals, that takes care of the horizon automatically. You can turn this backwards: if yo define the horizon incorrectly, the verticals will lean left and right.
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Gabor
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