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Author Topic: Alignment issues  (Read 5520 times)

david.bergbom

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Alignment issues
« on: November 09, 2015, 12:02:09 PM »
Hi,
I have 3 questions regarding photo alignment:

Background:

I have 1012 pictures (3000 x 4000 res., 1.38 GB) of a conveyor at one of our plants that I've tried to align with the "high" setting. Only about 3/5 of the pictures align and when I highlight the unaligned pictures and try "align selected pictures" they cannot align.

I've also tried aligning them with the "low" setting which yealds about 90% of the pictures aligned, and the ones that do not align I'm surprisingly also able to align by selecting them and pressing "align selected pictures".


Question 1: Does Photoscan "remember" any information from the "low" alignment that helps the software to continue with a finer alignment "medium" and then "high" in separate steps? That appears to be the case with these pictures that I'm now trying to align.

Question 2: If I have aligned the chunk with the "high" setting, when I later manually try the unaligned ones with "align selected pictures", does that align them in "high", "low", or "medium". The reason why I ask is that the pictures that successfully align with "align selected pictures" align almost instantly while the initial overall alignment of the pictures is rather time consuming. The fact that the initial alignment has a lot more pictures to go through is taken into account. 950 pictures took 30 minutes to align and the 60 pictures that later aligned with "align selected pictures" where done aligning after 2,5 seconds (2 of the pictures I wasn't able to align at all).

Question 3: What is the correct way to manually align the unaligned pictures? Is it best to highlight the unaligned pictures by them self or should some of the already aligned ones be highlighted together with them to get a better alignment result?

Best regards,
David Bergbom
LKAB Mekaniska AB
david.bergbom@lkab.com
+46 70 6853571

Alexey Pasumansky

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Re: Alignment issues
« Reply #1 on: November 09, 2015, 12:31:53 PM »
Hello David,

Starting Align Photos operation discards all the information regarding previous processing results (like matching points), so there will not be any benefit from using the align photos operation consequently with the different parameters.

The Align Photos operation itself consist of three major steps:
- detecting feature points on the individual images,
- matching these feature points across the images in the set,
- estimating the camera external and internal orientation using the matching points found on the previous step.
So when you use Align Selected Cameras option, only the third step is being executed and PhotoScan is trying to align the NA (not aligned) cameras using the existing matching point found during the Align Photos operation. It means that if there are no matching points on the certain image found the Align Selected feature wouldn't help.

You can use markers as valid matching points to help the Align Selected operation (at least four markers should be placed on every NA images, each of marker should be also defined by its projection on at least two images from the aligned sub-set).

But the alignment problem might be also related to the lack of the features on the surface being scanned or by the insufficient overlap between the images. You can send the aligned project to support@agisoft.com for the further investigation.
Best regards,
Alexey Pasumansky,
Agisoft LLC

JMR

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Re: Alignment issues
« Reply #2 on: November 09, 2015, 12:46:53 PM »
delete
« Last Edit: November 09, 2015, 12:51:09 PM by JMR »

david.bergbom

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Re: Alignment issues
« Reply #3 on: November 09, 2015, 01:14:08 PM »
Thanks for the replies,

I guess the Alexeys explanation of the quick alignment makes sense if only the 3rd step of the alignment is processed.

In response to step-by-step better alignment "low"-"medium"-"high", I guess JMR (Geobit) suggests that information from previous alignments is kept is subsequent alignments.

I'll try to give a better explanation of my two test-runs:

1, I added all the pictures in my picture folder and started the alignment on "high".

Result: 3/5 of the pictures aligned properly and none of the unaligned ones was possible to align using "Align Selected Cameras".

2, I added pictures step by step, just like JMR suggested, in a chronological order (trying to follow a logical order considering the way pictures overlapped - not the order the pictures were taken since my collegue had gone "back-and-forth" between different locations of the conveyor"). I ran a "low" alignment of these pictures (about 80 pictures) , where 90% of them aligned. The rest aligned with the "Align Selected Cameras"- function.

I then added the rest of the pictures in two more steps with new alignments (alining all pictures) in between, in "low". All the pictures but 2 were aligned.

After this, making no further changes to the chunk, I processed the whole alignment all over again in "medium", and after this in "high". All pictures are now aligned in "high".

JMR

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Re: Alignment issues
« Reply #4 on: November 09, 2015, 03:54:19 PM »
 ;) just did'n want to reply to Alexei's answer that is vastly better documented than I... but happy you succeeded.
Regards.