[2.5.0 A1] Free Nodal Point ability Vs ViewPoint correction  

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enbilaman
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[2.5.0 A1] Free Nodal Point ability Vs ViewPoint correction

by enbilaman » Fri Jun 25, 2010 6:12 pm

AlexandreJ wrote:* Free Nodal Point ability (quite the same as viewpoint correction in PtGui ). This feature is for Autopano Giga only.

I have had to upgrade from APP to AGP and be able to use this new feature.
I am quite familiar with the PTGui viewpoint correction and I am using it mostly to insert an oblique nadir view (hand held or not): this image is unobstructed by the panohead/tripod and allows by the same token to remove the ugly shadows of the tripod legs. AFAIK this is by far the most frequent use of the PtGui function and it's truly efficient as long as the "floor" of the panorama is flat enough. I must confess that I could not yet figure how to do the same achievement with the new "Free Nodal Point ability". With APG 2.5.0 A1 the result is a mess, so I beg to be told how can we select e.g. the oblique nadir shot to be solely affected by the "correction" (and letting all the other images be driven by standard "Nodal Point" restriction)?
It's also possible to use the ViewPoint correction of PTGui for other purposes (including what you, Alexandre, tell us about in the video) and automatic control point creation by PTGui works also fairly well in those cases.
When we decided to add Free Nodal Point Ability to our engine, we wanted it to be automatic. Normally when doing that, you cannot rely on automatically created control points. You need to enter them manually. Again, we think that an automatic solution that works should be created first. If it solves 90% of the cases, it's good. This is our goal which is why we have the new ransac stage 'full 3d'.

I loudly applaud your bet on CP creation automatism. But I believe that oblique nadir patching wont work if other automatisms can't be overridden e.g. to allow "correction" of only selected view(s). Automatic CP creation should IMO not be incompatible with "image selectable" Free Nodal Point ability.

With the current APG 2.5.0 A1 version, the assertion " Free Nodal Point ability is quite the same as viewpoint correction in PtGui" is debatable. Or did I miss something?

Regards,

Michel

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by taf » Fri Jun 25, 2010 9:57 pm

another question about the Free Nodal Point :

I make all my panorama handheld, without treepod. Is it better to select this option for all my panorama or only in few case if the detection is not good ?
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by vincen » Sat Jun 26, 2010 7:15 am

enbilaman wrote:With the current APG 2.5.0 A1 version, the assertion " Free Nodal Point ability is quite the same as viewpoint correction in PtGui" is debatable. Or did I miss something?

I don't think so ! ViewPoint correction in PTGui is mainly designed for stitch of nadir and zenith pictures in my idea. Free Nodal Point is definitively done for panoramas shots by hand, without taking care of nodal point ;)

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enbilaman
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by enbilaman » Sat Jun 26, 2010 9:37 am

vincen wrote:
enbilaman wrote:With the current APG 2.5.0 A1 version, the assertion " Free Nodal Point ability is quite the same as viewpoint correction in PtGui" is debatable. Or did I miss something?

I don't think so ! ViewPoint correction in PTGui is mainly designed for stitch of nadir and zenith pictures in my idea.

Hi Vincen,
You are most probably right:
Quoting from: http://www.ptgui.com/support.html#4_13
<< Please keep in mind that viewpoint correction was intended to be used on a single nadir image only, and all control points should be placed in a flat surface... >>
The ViewPoint correction feature was indeed mainly intended for this task as it had been anticipated and requested to do so for a long time by the user's community vast majority. And it does that admirably well.

vincen wrote:Free Nodal Point is definitively done for panoramas shots by hand, without taking care of nodal point ;)

Yes, fully agreed, but then I am greatly disappointed to observe that APG (Free Nodal Point ability) currently can't do what PTGui Pro (ViewPoint correction) can do. In contrast "ViewPoint correction" may be as effective as "Free Nodal Point ability" in dealing with panoramas shot by hand, without taking care of nodal point... while this feat was not firmly requested;)

Is there a technical hurdle that unavoidably causes (IMO) the unfortunate crippling of the performance of APG 2.5.0 A1?

BTW PTStitcherNG can be plugged in PTGui to warp and blend images for ViewPoint corrected panoramas. I wish to be able to use it in concert with APG as well.

Michel

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by gerardm » Sun Jun 27, 2010 3:51 am

alpha 1: wait.
working..
believe...

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by [bo] » Mon Jun 28, 2010 8:50 am

taf wrote:another question about the Free Nodal Point :

I make all my panorama handheld, without treepod. Is it better to select this option for all my panorama or only in few case if the detection is not good ?

Exactly my question from this post: http://www.autopano.net/forum/p65366-2010-06-24-17-47-51#p65366
Some of my panoramas, posted in the Autopano Pro flickr group.

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AlexandreJ
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by AlexandreJ » Mon Jun 28, 2010 2:51 pm

I don't know all details behind viewpoint correction in ptGui, but in our system, it allows to stitch images without concern of the NPP point.
In most case, as [bo] asked, we don't care, it's useless. In in most case, it's really nice like in the video. It's a paragliding panorama of the ground. It moves a lot and quickly, so you are not having the same viewpoint at each shot. This mode helps for such case. In fact, we identified 4 typical cases :
- nadir shots
- aerial shooting ( ballon, paraglider, planes, etc )
- flat object ( painting reproduction, etc )
- walls

I agree, there is still some bugs left to get to the point we want with this feature.

BTW : about one request : ability to enable that mode per image or not. We were wondering about that one too and we didn't decide if it should be done by image or globally yet. If it's just for one image, we should have a way to tell that before the detection. I don't know yet where to put that in the UI.

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by GURL » Mon Jun 28, 2010 3:36 pm

AlexandreJ wrote:BTW : about one request : ability to enable that mode per image or not. We were wondering about that one too and we didn't decide if it should be done by image or globally yet. If it's just for one image, we should have a way to tell that before the detection. I don't know yet where to put that in the UI.

Default : Free or not free is global
Contextual menu in the Group window (for any image) : Free Nodal Point = Yes/No

One related question: I tested this feature using a fisheye and found (in the Layers window) that X, Y values of crop circles had unusually large values. Is this related to using Free nodal point ?
Georges

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by HansKeesom » Tue Feb 01, 2011 1:01 am

Is this feature effective when shooting a pano in heavy sunlight, causing a shadow of tripod and camera? If so, what would be the best technique for the last shot. Would one have to place the tripod past the end of the shadow and make one shot of where the tripod was standing, so make one photo against the sun of the nadir?
Regards, Hans Keesom
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by enbilaman » Tue Feb 01, 2011 11:24 am

HansKeesom wrote:Is this feature effective when shooting a pano in heavy sunlight, causing a shadow of tripod and camera? If so, what would be the best technique for the last shot. Would one have to place the tripod past the end of the shadow and make one shot of where the tripod was standing, so make one photo against the sun of the nadir?

Yes! It's often better to have the sun in a lateral direction rather than straight ahead to obliquely shoot the Nadir from an different viewpoint. But your stated principle would be possible only if the Nadir image(s) could be individually treated with viewpoint correction in the way (too) briefly considered by Alexandre:
AlexandreJ wrote:... This mode helps for such case. In fact, we identified 4 typical cases :
- nadir shots
.... etc.

If such an option was offered and if the shadow of the tripod (and possibly also of the photographer!) is only present on a unique flat surface (e.g. only on the floor and not partly on the wall), this method would quasi-miraculously remove the panohead/tripod obstructions as well as inopportune shadows from the Nadir of the panorama. PTGui users benefit already from this feature. I miss it and I sincerely wish to get the same ability with APG soon.
Sorry to insist but I had suggested such an approach in the OP. The months that lasted since then have not made my mind to change a bit on that matter.

Michel

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by HansKeesom » Tue Feb 01, 2011 12:19 pm

Hi Michel, so instead of moving in the direction of the shadow, I move a meter in a direction 90 degrees on the shadow and make one shot of the nodal point. I will test it and make even two shots as there are two directions one can go for this
Last edited by HansKeesom on Tue Feb 01, 2011 12:20 pm, edited 1 time in total.
Regards, Hans Keesom
I stitch and render for other photographers. Price: 25 euro or less, no cure no pay. If you want to concentrate on your business let me do the stitching for you. Free TB of Dropbox space when you have more then 250 euro business a year.

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enbilaman
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by enbilaman » Tue Feb 01, 2011 1:43 pm

HansKeesom wrote:Hi Michel, so instead of moving in the direction of the shadow, I move a meter in a direction 90 degrees on the shadow and make one shot of the nodal point. I will test it and make even two shots as there are two directions one can go for this

Testing different positions for shooting Nadir oblique views is IMO a very good idea:
One shall then learn that the specular reflexion of the sunlight onto the ground (or on the floor) is sometimes problematic: when/if the floor is highly reflective, care has to be taken to shoot in the adequate direction w.r.t. the sun incident rays in order to have the very best Nadir oblique patch that matches well with the other images before inserting it into the panorama (Note: blending may anyhow help to nicely hide the mismatch along the seams).

Michel


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