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Messages - patcarbon

Pages: 1 [2]
General / The mysterious 'bowl effect'
« on: July 27, 2012, 11:57:29 AM »
I've seen a few references to this bowl effect on pages here.  i've also seen what looks like the bowl effect in data.  In fact, this was in images taken with the UAV produced by the Swedish re-seller of Photoscan, SmartPlanes.

What causes this?  Since the effect coveres a whole scene, in my case with over 200 images, I have always assumed that it can't be lens distortion since the bowl fits a 2nd order surface.  When is this distorsion introduced?  Alignment? Build Geometry? Georeferencing?  Surely it's in one of the first 2 since, if I understand right, georeferencing just uses a rigid 7-parameter transform so that means the 'bowl has to be generated earlier'.  Correct?

And what's the maths behind the optimisation?  It it relying on a photogrammetry-style epipolar constraints approach?


General / Number of images vs final number of vertices?
« on: July 25, 2012, 09:12:47 PM »

What is known about the relationship between the number of photos going into Pscan (or any other SfM routine) and the final number of vertices in the raw point cloud?  Can anybody point my to some literature in computer vision/SfM research?


Feature Requests / Autosave after aligning chunks
« on: July 06, 2012, 11:06:22 AM »
A very little thing:  the align chunks function, which can take a while for big multi-chunk projects, should at least have a checkbox option to save after completion.  Or alternatively, add this function to the batch process dialog where the option to save does exist.


General / Exporting vertices
« on: July 04, 2012, 04:26:05 PM »

Is there an easy way to export the vertices of a calculated model?  The way I understand the exports, if you 'export model' you get the mesh, not the point cloud (or at least the point cloud comparison software I'm using only sees the mesh).  But then if you export points and re-select the desired quality, it seems to reprocess the model.

So what I want is to export a dense point cloud for data which has already been aligned and built.

What's the quickest way?


General / Improving chunk alignment
« on: November 17, 2011, 03:53:56 PM »
For my type of Images, I've found that the automated chunk alignment can give bad results.  There are many similar features, and the system I'm looking at even has some fractal characteristics so cross-scale similarities exist.

So I was wondering if the following is possible:
1-  Manually align the chunks with 3 markers.
2- Optimise this alignment, hopefully to sub-pixel accuracy, with an automated match run.

So I'm hoping that with 2 approximately aligned chunks, the pattern match algorithm will limit it's search area via some sort of epipolar constraints and thus reduce false positive matches.  Can this be done in 8.4?


Bug Reports / Zooming bug
« on: November 14, 2011, 11:39:00 AM »

I'm working with 2 chunks of approx 200 images.  When I register the first chunk to map coordinates, I sometimes have problems with the zoom function.  I often just can't see one of the models, as if I was zoomed out way too much or too little.  Since the scale of the un-registered and registered DEMs is so different, it becomes a nightmare to manage the zooms.  GIS packages and photogrammetry software all have a 'reset view' or 'fit to frame' command.  We need one!  In the meantime, is the a python command I can use in the console?


General / Using camera external orientation
« on: August 25, 2011, 04:19:56 PM »
Hi, sorry if some of these questions are obvious but I'm new with photoscan.

So I want to use a photo dataset generated by a UAV (usually between 100-300 pics).  The UAV produces camera position and orientation so the obvious thing to do is to use those instead of ground control points.  A few things that weren't clear from the manual:

1- What is the naming convention for the XML files?  How can I produce these in a way that photoscan will easily import a few hundred and correctly link each file to the correct photo?
2-How does photoscan handle error in the external orientation?  Is there a least squares adjustment?  Does it warp the DTM to fit external orientation (EO) or does it adjust the EO and preserve the DTM?
3-Where in the workflow should I import the EO? Before or after the alignment?

Many thanks

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