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Author Topic: Aligning Chunks  (Read 5922 times)

Paul

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Aligning Chunks
« on: January 19, 2013, 02:28:39 PM »
Hello all

I'm using the standard edition to generate models of small objects but I'm have some difficulty with alignment. Any advice would be appreciated.
My current workflow:
Photograph the object, 3-4 circular patterns about 10 degrees each, offsetting each pattern by about 30 degrees depending on the object. This give me about 120 images.
import all images and mask off the background in PhotoScan
Usually PS wont align al the images at once so I group each circular pattern in a Chunk.
However PS won't align the Chunks without altering the separate alignments and making a mess of the model.
I've tried disabling some images and only aligning selected images but this is unsatisfactory.

Is their an alternative workflow?

I've considered building each Chunk and using MeshLab to align each mesh/point cloud but PS has much better texture mapping. Is is possible to re-import the model to PS and texture map the model?

Cheers

Im using the latest build of PhotoScan standard
Hardware: Dell T7400, Quad Xeon, Quadro FX3700, 16GB Ram, Ubuntu 12.10 64bit

RalfH

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Re: Aligning Chunks
« Reply #1 on: January 19, 2013, 03:28:14 PM »
For a project of 120 images it should be possible to work without using chunks. If there are many misalignments after the initial alignment step, my usual workflow is the following:
- look for a subgroup of images which appears to be well aligned
- reset alignment for all remaining images
- individually align the remaining images one by one
- check alignment after each image alignment (both by looking at the point cloud and modeled camera positions and by looking at the numbers in the refined camera calibration - if the refined calibration parameters - in particular focal length - are more than a few per cent off the initial parameters, I assume that that camera is not well modeled and misaligned)
- if an alignment looks bad, reset that alignment and skip that image (perhaps try to align it again at the end after all other images are well aligned)

This can take some time but in my experience can result in good models even if things looked horrible after the initial image alignment. Also, try to use "separate" under refined camera calibration, in particular if you have movement within the lens systems beween photos (e.g., focussing, optical image stabilisation) which would not be taken into account if you used "groups".
« Last Edit: January 19, 2013, 03:29:50 PM by RalfH »

Paul

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Re: Aligning Chunks
« Reply #2 on: February 01, 2013, 02:18:35 PM »
Thanks for the advice, however the images would not align.
I'm trying some other patterns, perhaps my orbits were too radical for the software to match up.
Cheers

Paul

RalfH

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Re: Aligning Chunks
« Reply #3 on: February 01, 2013, 02:25:04 PM »
Can you upload your images somewhere so I can check what could be the problem?

Paul

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Re: Aligning Chunks
« Reply #4 on: February 19, 2013, 05:41:46 PM »
Hi RalfH

Sorry about the delay in getting back to you, other projects took over. Unfortunately I cant send you the current batch of images (license restrictions).

I'm still having difficulty aligning sets of images, in the next week or so I'll try again with a new batch, which I'll have broader scope to use and take you up on your offer then.

Many thanks

Paul