feature suggestion for horizontal and vertical control lines

[Othman Bouizi]

Hello,

As everyone here, I am adding vertical and horizontal lines to control the shape of the panoramas. However, there are few features that could help achieve a good panorama composition.

a) when adding a vertical or horizontal line, this one does not materialize on the picture in the Control Points tab and in the Panorama Editor. It could be helpful to straighten a tower that has no vertical boundaries or to check the verticality in the editor.

b) when a horizontal or vertical line's extremities are on two different photos, the distance between the two extremities appears as "non-void", unlike the horizontal or vertical line that belongs to the same photo. I suggest that every horizontal and vertical line to be considered as it.

c) related to the remark b), can you provide as a "distance" for the horizontal or vertical lines their angle with the horizon or with the vertical. So that we can appreciate the deviation of the panorama from the ideal horizon (or vertical) ?

d) when the panorama has an horizontal line, why the tool "straightening the panorama" changes its shape and deviates from the instruction of the user ?

Cheers,

Othman.

[PTGui Support]

Hi Othman,

In general you should use vertical lines for leveling spherical
panoramas. This is because in equirectangular projection all horizontal
lines are curved but all vertical lines are straight.

See the video tutorials, part #8 for more information:
https://www.ptgui.com/videotutorials.html

That said, I agree the leveling procedure in PTGui is not entirely
straightforward and can be improved.

Kind regards,

Joost Nieuwenhuijse
www.ptgui.com

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[Othman Bouizi]

Hi Joost,

Thanks for the quick answer :)

I agree with you about the "verticals" that help levelling spherical panoramas (it's maths after all !).

Coming back to the horizontals, maybe then one should distinguish between horizontals in a rectilinear projection (to straighten a single image) and a single horizon line. My understanding of the video tutorial part #8 is that the "horizontal" in PTgui represents the "horizon line". There can only be one "horizon line" per image, and by extension only one "horizontal line" per image. Or am I wrong ? If not, can we imagine consider that one can only set one horizontal line per image and no horizontal line on 2 different images ?

Regards,

Othman.

[Erik Krause]

Am 21.10.2021 um 17:03 schrieb Othman Bouizi:
> There can
> only be one "horizon line" per image, and by extension only one "horizontal
> line" per image. Or am I wrong ? If not, can we imagine consider that one
> can only set one horizontal line per image and no horizontal line on 2
> different images ?

There is only one horizon but you can of course define multiple
horizontal lines (on the horizon) in one panorama. And you should do so,
if there are problems leveling and you have no verticals.

This is true for all projections but rectilinear, where all horizontal
structures can have horizontal lines. You can use that to remove
horizontal perspective distortion:
https://wiki.panotools.org/Perspective_correction#Camera_panned_sideways

--
Erik Krause
http://www.erik-krause.de

[John Houghton]

On Thursday, October 21, 2021 at 4:03:48 PM UTC+1 othman...@gmail.com wrote:

. . . . If not, can we imagine consider that one can only set one horizontal line per image and no horizontal line on 2 different images ?

Note that when creating a vertical line point or horizontal line point, the two ends of the line feature being marked may lie in different images when the feature spans multiple rows/columns. So you do not necessarily display the same image in the two windows of the Control Points tab when creating such points.  Moreover,  there may not be an actual straight line feature involved.  For example, the reflection of an object (treetop, say)  in the surface of still water should be vertically aligned and so you can use a vertical line control point to achieve that alignment to assist in the levelling process.  However, when two different images are displayed,  you will need to select the control point type manually.  When the same image is displayed, PTGui will default the control point type to vertical line.

John

[Othman Bouizi]

Hello Erik and John,

Thanks for your answer. Now I understand why a vertical line is the "default"  (but I would prefer this to be automatically set depending on the angle of the line, set by the user, with the vertical of the screen. The user can also change the type of the line)

@Erik, I agree with you, the use of rectilinear projection can felp to remove a horizontal perspective distortion. But in the case of other projections (cylindrical, equirectangular), which of the horizontal lines is used to be aligned with the horizon of the final image ? In the video #8 pointed by Joost, at 4'02", it is said that the horizontal line is used in conjunction with the horizon. So, what happens with two horizontal lines that are not aligned (let's say parallel) in an image ?

@John, okay, then what's your thought on materializing/displaying the line on the panorama preview, to assist also manual leveling or assist to place correctly the horizontal lines in the images ?

Othman.

[John Houghton]

On Saturday, October 23, 2021 at 1:34:08 AM UTC+1 othman...@gmail.com wrote:

@John, okay, then what's your thought on materializing/displaying the line on the panorama preview, to assist also manual leveling or assist to place correctly the horizontal lines in the images ?

Othman, I don't think there is much to be gained by materializing the line on the Panorama Editor window.  (Would it be curved to follow the current shape of the "straight" feature?).  The only advantage for me would be that any error in the setting of the correct control point type or in the placement of the points would be more obvious.  But there is already assistance for manual levelling:  if you drag the tiny triangle at the bottom of the frame to the right, you can display a grid of variable size to enable the levelling to be checked.

John

[Erik Krause]

Am 23.10.2021 um 02:34 schrieb Othman Bouizi:

> So, what happens with two horizontal lines
> that are not aligned (let's say parallel) in an image ?

There is only one horizon, hence there can't be parallel horizontal
lines in any projection but rectilinear. You can mark different parts of
the horizon though, but it must be the true horizon.