Misaligned horizon - Phantom 4 with Dronepan 360 x 180

Damian Witham

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Jun 16, 2016, 8:39:26 PM6/16/16

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I'm just new with these and I am having a similar problem with each pano I do. There are 1 or 2 areas where the horizon just wont match right. Like this.

If anyone has time and is interested I have included all files here:

https://www.dropbox.com/sh/zipcfgn0ardz981/AAA2QSFNiahRFGqPSuvePd6Ea?dl=0

As you can see i am also getting a wavy horizon which I also need to fix. But the question is, do i fix the wavy first, then fix the misalignment or the other way around.

To me the misalignment is the crucial part that needs fixing.

PTGui Support

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Jun 17, 2016, 4:28:00 AM6/17/16

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Hi Damian,

I think it's parallax, it looks like the left and right images have been
taken from quite different altitudes. You can't stitch these perfectly.

If you go to a higher altitude the parallax will give less problems
because there are no objects close to the camera.

Kind regards,

New House Internet Services BV
Joost Nieuwenhuijse

-----------------------------------------------
PTGui - Photo Stitching Software

www.ptgui.com
For support see: http://www.ptgui.com/faq/
-----------------------------------------------

On 17/06/16 02:39, Damian Witham wrote:
> I'm just new with these and I am having a similar problem with each pano
> I do. There are 1 or 2 areas where the horizon just wont match right.
> Like this.
>

> <https://lh3.googleusercontent.com/-bvpxTl5Pbrw/V2NGD8NMtLI/AAAAAAAAAR0/nKG7R-tbEHgj-t_mwRboa7RPbuF0Lt3owCLcB/s1600/misaligned.jpg>

>
>
> If anyone has time and is interested I have included all files here:
>
>
>
> https://www.dropbox.com/sh/zipcfgn0ardz981/AAA2QSFNiahRFGqPSuvePd6Ea?dl=0
>
> As you can see i am also getting a wavy horizon which I also need to
> fix. But the question is, do i fix the wavy first, then fix the
> misalignment or the other way around.
>
> To me the misalignment is the crucial part that needs fixing.
>

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John Houghton

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Jun 17, 2016, 9:25:41 AM6/17/16

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On Friday, June 17, 2016 at 1:39:26 AM UTC+1, Damian Witham wrote:

I'm just new with these and I am having a similar problem with each pano I do. There are 1 or 2 areas where the horizon just wont match right.

I'm not surprised that you are having a few difficulties stitching these images. You've got the lot: brightness differences, auto exposure, auto white balance, horizontal and vertical parallax. I started by aligning only the top row to get the horizon reasonably straight and level by having control points only on the most distant features. I then aligned the remaining rows to the first row.. I output a PSB layered file and let CS6 do the auto-blending. I still had a small glitch on the horizon, which I corrected in Photoshop. Otherwise, the stitch is far from perfect, but FWIW can be downloaded from https://www.sendspace.com/file/pwyguh .

John

CBSystem46

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Jun 18, 2016, 7:54:19 PM6/18/16

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Hello,

I can confirm that I almost have this kind of problem with horizon every time, even with far objects and high altitudes.

For exemple :

or

I was hopping that it would be fixed in the last release but I still have this problem on quite easy part of the picture. The other parts of the picture are perfect but it's hard to sell the result to a customer with this kind of issue.

I also tried to made a pano with Lightroom with the same pictures and it's perfect with it, but it doesn't work for 360. And with PTGui I always have 1 or 2 issues on each picture. Could you tell us how to fix it ?

Thank you

PTGui Support

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Jun 19, 2016, 2:01:51 AM6/19/16

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Hi,

In order to stitch panoramas with PTGui all images have to be taken from
exactly the same viewpoint. If this is not the case, there will be
parallax. Images with parallax cannot be stitched perfectly; they will
result in misalignments, wavy horizon etc.

If you are close to the ground camera position is very critical. Even if
the camera has moved only a few centimeters, stitching errors will be
visible. Higher in the sky the problems will be less pronounced but you
would probably still need the camera to be steady within a meter or so
for perfect results. I'm not familiar enough with current drone
technology to know if this is feasible or not.

There are some tricks to somewhat improve the result:
- ensure that all control points are placed only on objects far away:
this will make sure that at least the horizon will be aligned perfectly
(but at the cost of stitching errors on foreground objects).
- try enabling viewpoint correction on all images except one. This would
improve alignment at the horizon as well, but could result in slanted
buildings and also stitching errors in the foreground. For more on
viewpoint correction see
http://www.ptgui.com/examples/vptutorial.html

But if there's any parallax be prepared to spend considerable time
tinkering and retouching to get good results.

If PTGui does not match your expectations or you are unhappy in any way
just contact me at support at ptgui dot com to return the software for a
refund.

Kind regards,

New House Internet Services BV
Joost Nieuwenhuijse

-----------------------------------------------
PTGui - Photo Stitching Software

www.ptgui.com
For support see: http://www.ptgui.com/faq/
-----------------------------------------------

On 19/06/16 01:54, CBSystem46 wrote:
> Hello,
>
> I can confirm that I almost have this kind of problem with horizon every
> time, even with far objects and high altitudes.
>
> For exemple :

>
>
> I was hopping that it would be fixed in the last release but I still
> have this problem on quite easy part of the picture. The other parts of
> the picture are perfect but it's hard to sell the result to a customer
> with this kind of issue.
>
> I also tried to made a pano with Lightroom with the same pictures and
> it's perfect with it, but it doesn't work for 360. And with PTGui I
> always have 1 or 2 issues on each picture. Could you tell us how to fix it ?
>
> Thank you
>
>
>
>
>
> Le vendredi 17 juin 2016 10:28:00 UTC+2, PTGui Support a écrit :
>
> Hi Damian,
>
> I think it's parallax, it looks like the left and right images have
> been
> taken from quite different altitudes. You can't stitch these perfectly.
>
> If you go to a higher altitude the parallax will give less problems
> because there are no objects close to the camera.
>
>
> Kind regards,
>
> New House Internet Services BV
> Joost Nieuwenhuijse
>
> -----------------------------------------------
> PTGui - Photo Stitching Software
>

> www.ptgui.com <http://www.ptgui.com>

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> > <mailto:ptgui+un...@googlegroups.com <javascript:>>.

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> > <mailto:pt...@googlegroups.com <javascript:>>.

> > Visit this group at https://groups.google.com/group/ptgui

> <https://groups.google.com/group/ptgui>.

> > To view this discussion on the web visit
> >
> https://groups.google.com/d/msgid/ptgui/42bbeb3f-62d0-49c1-b442-b28fc6f926bf%40googlegroups.com
> <https://groups.google.com/d/msgid/ptgui/42bbeb3f-62d0-49c1-b442-b28fc6f926bf%40googlegroups.com>
>
> >

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>
> > For more options, visit https://groups.google.com/d/optout

> <https://groups.google.com/d/optout>.

>
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John Houghton

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Jun 19, 2016, 9:07:41 AM6/19/16

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You might try the free Microsoft ICE package. It puts in a very creditable performance, but again is unable to do the impossible and generate a perfect stitch: https://www.sendspace.com/file/fm8rsw .

John

CBSystem46

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Jun 19, 2016, 10:17:50 AM6/19/16

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Thank you for your answer,

I don't want any refund, I just would like to fix some issues :-)

I guess your software is and will be used a lot by DJI drone users with our without the dronepan application to make 360° view and actually there are some little issues on horizon almost every time that's why we all hope you can find a good solution to fix it automatically because 99% of the view is prefect !

Thank you for your support

CBSystem46

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Jun 19, 2016, 10:20:51 AM6/19/16

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Hi John,

I tried ICE before and it was working fine but I had issues with Pano2VR to make the view where PTGui was working fine

Damian Witham

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Jun 19, 2016, 6:55:25 PM6/19/16

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Thanks for reply PTGUI Support,

Looks like the altitude drops with the phantom are the main cause. I have indeed found the higher I go the better the stitch. Bit of a bummer, but nothing that PTGUI can fix. I guess I need to get better at mastering the control points and masking.

Damian Witham

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Jun 19, 2016, 7:02:16 PM6/19/16

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Thanks for having a look John and doing what you can with it. I can see I need to take a different approach and set up the camera properly before I take the shots. I'll learn that first. I was interested in the way you worked through this by stitching just the top row first. I am unaware of all the tricks that you can do with PTGUI. It's kind of hard to find the resources to learn all of that. Is there somewhere that you know that has this type of information?

Damian Witham

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Jun 19, 2016, 7:03:28 PM6/19/16

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CBSystem46 it looks like you have the same issues i face. Keep in touch and we'll see if we can work this out together.

John Houghton

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Jun 20, 2016, 3:48:22 AM6/20/16

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On Monday, June 20, 2016 at 12:02:16 AM UTC+1, Damian Witham wrote:

Thanks for having a look John and doing what you can with it. I can see I need to take a different approach and set up the camera properly before I take the shots. I'll learn that first. I was interested in the way you worked through this by stitching just the top row first. I am unaware of all the tricks that you can do with PTGUI. It's kind of hard to find the resources to learn all of that. Is there somewhere that you know that has this type of information?

There are many tutorials to be found on the web, but there's very little to help with stitching shall we say "badly shot" panorama images. Mostly it's just a question of understanding how to control the optimizer in it's advanced mode. Using the array of check boxes, you can precisely control just what the optimizer is allowed to do on a per image basis. For example, if you want to align the single row of images covering the horizon, you can either (a) load only those images in to begin with and align them on their own, or (b) use the check boxes for just that row of images and only check those images in the "Use control points of" list. Effectively, all the other images will be ignored by the optimizer and their current positions in the output area will will remain unaffected when you run the optimizer. After (a) you can go on to load in another row or rows of images via the Project Assistant tab or the Source Images tab. Lock the aligned horizon row in position by unchecking their y,p,r boxes so the optimizer cannot shift them in subsequent runs.

There's a couple of rather old articles about optimization:

A brief note: http://wiki.panotools.org/Optimization

More detailed: http://www.johnhpanos.com/optitute.htm

Although written in general terms for Panorama Tools front end packages, PTGui no longer makes any use of these, but the same basic principles still apply.

John

Anthony

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Jun 20, 2016, 10:56:16 AM6/20/16

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We've been shooting aerial panoramas for close to 10 years beginning with RC helicopters using modified camera mounts and DSLR cameras and now using multicopters. The "notched horizon" is a result of parallax due to movement of the aircraft and camera between photos. Joost described it perfectly. There's no way around it because no aircraft will hold its position perfectly to allow the camera to rotate around the entrance pupil for the duration of the entire image capture process. You have to use Photoshop or similar image editing software to correct the errors. Most are easy fixes but there are techniques that will give much better results. Brush up on those skills. This isn't an issue with the panorama app or PTGui. Currently there are limitations in the DJI software which slow down the image acquisition process. Once this hurdle is crossed, stitching will become easier with less Photoshop fixes being needed in post.

Tony

On Thursday, June 16, 2016 at 7:39:26 PM UTC-5, Damian Witham wrote:
> I'm just new with these and I am having a similar problem with each pano I do. There are 1 or 2 areas where the horizon just wont match right. Like this.
>
>
>
>
>

Roger Broadie

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Jun 20, 2016, 5:04:33 PM6/20/16

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On 19 June 2016 at 23:55, Damian Witham <dog...@gmail.com> wrote:

Thanks for reply PTGUI Support,

Looks like the altitude drops with the phantom are the main cause. I have indeed found the higher I go the better the stitch. Bit of a bummer, but nothing that PTGUI can fix. I guess I need to get better at mastering the control points and masking.

Damian,

I'm not sure it's just changes in altitude that is the problem. I think there is some instability in the positioning of the drone, probably as much horizontally as vertically. Thus if you look at the shed (if that is what it is) behind the two two large pale storage drums visible in image 1 (i.e. DJI_0040) and image 29, the first shows rather more of the downward slope of the roof beyond the ridge than the second. That seems to me a certain indication that the drone has moved. I can't believe that rotating the camera in its mounting could cause that degree of parallax, or even any noticeable parallax at the distances involved.

So if it is feasible for you to keep the drone more stable in position that looks well worthwhile.

I put your images into PTGui and pressed Align in the Project Assistant. That produced a recognisable though not perfect stitch, though the wavy appearance was quite distracting. Also noticeable were the flaw you have illustrated where the seam between images 4 and 8 crossed the horizon, and, not surprisingly, a mismatch where the seam between images 1 and 29 crossed the shed/storage drums structures in images 1 and 29.

However, when I then opened the Optimiser in the Advanced mode and pressed Run, PTGui reported that the stitch had failed. It characterised it as "bad", with an average control-point distance of 21 and a maximum of 111. It did not find any of the points to be statistical outliers that could be deleted. One side effect was that there were a lot of control points in the sky, many of which were obviously unsound because the clouds had changed position and shape. I think the program was caught out by the parallax, which give such a wide range of control-point distances that control points on changing clouds could not be singled out for deletion as being statistical outliers. I think - someone can tell me if I am wrong - that PTGui depends on that approach to eliminate unreliable control points on clouds. Although there may be other approaches to dealing with this problem, I simply deleted all control points in the sky I could find, which much improved the stitch.

As part of the reoptimising I set out to remove the wavy effect, which makes it difficult to evaluate the quality of the stitch. John Houghton (17 June 2016) has indicated one approach. But here it struck me that the drone was doing a pretty good job of keeping the top row (images 0, 4, 8 etc) level and I simply anchored one of the top row images (image 8, as it happens) by setting its pitch and roll at zero in the Images Parameters tab and making sure those values were non-optimisable in the Optimiser tab. That gave a reasonable if not perfect result - better, at any rate than I managed with the recommended method of attaching vertical control points to suitable structures. I also (and this requires PTGui Pro) ticked the viewpoint correction boxes for all the other images. This is a technique Joost suggested (19 Jun 2016). He warned that distortions can result, and here I rather suspect that a slight distortion of the horizon has occurred. It can be undone by reverting to the non-viewpoint-correction mode.

But sticking with viewpoint correction, the result after optimisation and some weeding of control points was an average control point distance of 1.3 pixels and a maximum of 6.0 pixels - a "very good" result. But we are not quite out of the woods yet, because as well as the mismatch between images 1 and 29, which has been reduced but not eliminated, there is a slight but I think ineradicable glitch in the horizon between images 4 and 8, where vertical parallax shows in the relationship between the land features and the horizon at sea. For these pairs we have to shift the seams out of the way by masking.

The sky as delivered by PTGui is a bit lifeless, but if you prefer and have the Pro version you could output a tone-mapped version with a more dramatic sky and combine this with the normal output, or even use it instead.

No doubt by taking your panorama from a higher altitude you could reduce the effects of parallax, but it seems a pity if panoramas like the one you have shown us are unachievable. In this case at least PTGui can help.

My pto file and a half-size stitch can be found here:

https://www.sendspace.com/file/asfiq6

Roger Broadie

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Damian Witham

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Jun 20, 2016, 6:37:09 PM6/20/16

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Wow Roger. Great commentary. Your workflow has opened my eyes. I only wish you screen recorded your process so I could see where you implemented each command. I'll see if i can follow along with your instruction. Thanks for taking the time. It's also good to know I'm not the only one with the steps horizon. Seems to be a common occurrence.

Roger Broadie

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Jun 21, 2016, 7:01:00 AM6/21/16

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Damian,

Thanks for the comments). Unfortunately, since I was exploring the possibilities I didn't arrive at my solution in a linear manner. However, by good fortune, I do have a pto file with no viewpoint correction and no sky control-points either (Witham-a novps.pto). Actually, it gives a good stitch (Witham-a novpsh), despite large reported control-point distances, except for one factor. The seam between images 4 and 8, though displaced by masking so that the section of the horizon out to sea visible in this area is glitch-free, now shows in a glitch in the path nearby. No doubt this can be eliminated by post-processing, which might be assisted by changing the masking. But I haven't found any way of doing it inside PTGui, short of introducing widespread viewpoint correction.

Such viewpoint correction does indeed seem to introduce some overall distortion. It can be seen by comparing its Panorama Editor (PE) view with that of the non-viewpoint correction case. With viewpoint correction the columns headed by images 24 and 28 are slightly lifted from the extreme regularity of the non-vp-correction case. As that exaggerates the height of the hill to the left of the foreground house, it may be objectionable

I've put the various files here:

https://www.sendspace.com/file/b4nfg6

Roger Broadie

On 20 June 2016 at 23:37, Damian Witham <dog...@gmail.com> wrote:

Wow Roger. Great commentary. Your workflow has opened my eyes. I only wish you screen recorded your process so I could see where you implemented each command. I'll see if i can follow along with your instruction. Thanks for taking the time. It's also good to know I'm not the only one with the steps horizon. Seems to be a common occurrence.

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Erik Krause

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Jun 21, 2016, 7:40:14 AM6/21/16

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Am 21.06.2016 um 13:00 schrieb Roger Broadie:
> Such viewpoint correction does indeed seem to introduce some overall
> distortion.

Yes of course. As outlined in various places viewpoint correction works
best for flat surfaces. Anything that protrudes from the surface gets
distorted.

See http://www.ptgui.com/examples/vptutorial.html under "Perspective
correction of flat images" and the last image above "Troubleshooting"

--
Erik Krause

Roger Broadie

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Jun 21, 2016, 9:58:46 AM6/21/16

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Yes, I do realise that viewpoint correction was intended for stitching images of flat surfaces. What was interesting and surprising in the case of the drone panorama I was considering was that all-around viewpoint correction, which absolutely disobeys the injunction in the tutorial you mentioned:

"Since viewpoint correction only works on flat surfaces, any image which is viewpoint corrected must only have control points placed on a single flat surface",

was so successful, with a striking reduction in the average control-point distance, no introduced stitching flaws that I noticed and only a mild overall distortion.

I also thought it interesting to see the nature of the distortion that did occur in this case set out so graphically in the two screen-grabs of the panorama editor I tabled.

Roger Broadie

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Erik Krause

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Jun 21, 2016, 10:08:15 AM6/21/16

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Am 21.06.2016 um 15:58 schrieb Roger Broadie:
> What was interesting and surprising in the case
> of the drone panorama I was considering was that all-around viewpoint
> correction,

[...]

> was so successful, with a striking reduction in the average control-point
> distance, no introduced stitching flaws that I noticed and only a mild
> overall distortion.

In fact I often use all-around viewpoint correction myself, especially
for handheld shots. As a side effect sometimes I have to straighten up
buildings :-)

Technically the optimizer gains some more degrees of freedom this way
which reduces control point distance of course.

--
Erik Krause

John Houghton

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Jun 21, 2016, 12:08:24 PM6/21/16

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On Tuesday, June 21, 2016 at 2:58:46 PM UTC+1, Roger Broadie wrote:

Yes, I do realise that viewpoint correction was intended for stitching images of flat surfaces. What was interesting and surprising in the case of the drone panorama I was considering was that all-around viewpoint correction, which absolutely disobeys the injunction in the tutorial you mentioned:

I, too, have used vp correction for stitching aerial 360x180 panoramas. In my case they were shot from the tops of towers rather than from drones or other aircraft and with very large degrees of parallax to cope with (being shot handheld from various points around viewing galleries rather than a single point. Reasonably flat landscapes don't pose too many problems, but when you have tall buildings sticking up to cope with, things are decidedly more difficult. One such panorama was my View From The Shard in London: http://www.johnhpanos.com/spherical/shard2/shard2.html for which I took 42 shots.

John

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