Bug in stereographic projection?

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Punkie
Posts: 51
Joined: Wed Jan 30, 2008 10:30 am
Location: Netherlands

Bug in stereographic projection?

Post by Punkie » Fri May 31, 2013 9:30 am

I'm trying to make a "planet" with PTA.
Input is an uncropped equirectangular image FOV 360 x 131.Vertical is from -90 to +41.
Just want to remap it in stereographic for a planet.

In the preview window:
First I centered it in the nadir. No zenith.
Autosized FOV. Becomes 360x180.

Then I select stereographic projection. and click Re-Draw.
Then PTA stitcher crashes. Following message comes from PTAssembler.
Cannot find output file from stitcher:D:\Temp\pta_preview_00000000.tif.
Checked if the file is in the temp folder.It is gone.
Have checked it before clicking the redraw button and it was in the folder.

Further when I change under the "Lens and global settings" the panorama projection to stereographic and go to the "preview and create" tab and press autosize parameters then the height of the pano becomes 0.
Is there something wrong with creating stereographic images from 360 equirectangular images?
When trying a lot of other projections I don't have that problem of a crashing PTAstitcher.
When setting back to equirectangular you still can create a new preview without closing PTAssembler.
In Hugin there you can create a stereographic image from an uncropped jpeg.
Tried straight to stitch a stereographic image from the original rectilinear pictures and the same crash.
I've tested it in PTAssembler 6.1, 6.0 and 5.1.
Is it a bug in PTAssembler or am I doing something wrong?

Kind regards,
Henk Tijdink

maxlyons
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Joined: Fri Jun 20, 2003 8:55 pm
Location: USA
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Re: Bug in stereographic projection?

Post by maxlyons » Sat Jun 01, 2013 4:56 pm

Henk,

I can replicate this behavior. I'll take a look.

Max

Punkie
Posts: 51
Joined: Wed Jan 30, 2008 10:30 am
Location: Netherlands

Re: Bug in stereographic projection?

Post by Punkie » Wed Jun 26, 2013 4:34 pm

Hello Max

Do you have any results with the stereographic projection?
Is it a bug?

Kind regards,
Henk Tijdink

maxlyons
Posts: 3649
Joined: Fri Jun 20, 2003 8:55 pm
Location: USA
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Re: Bug in stereographic projection?

Post by maxlyons » Wed Jun 26, 2013 11:19 pm

Sorry...I haven't had time to dig into this yet. But, I hope to address this before the next release of PTAssembler.

Max

maxlyons
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Re: Bug in stereographic projection?

Post by maxlyons » Mon Aug 19, 2013 10:41 pm

maxlyons wrote:Sorry...I haven't had time to dig into this yet. But, I hope to address this before the next release of PTAssembler.
I spent some time looking at this tonight. It takes me quite a while each time I have to dig into questions about projections because I have to re-educate myself with the code and the math before I can say anything useful!

PTAssembler uses the formulas found on Mathworld for this projection. I think the issue is that the stereographic projection is undefined when the longitude (i.e. yaw) value reaches 180 degrees (the value for "k" goes to infinity, and so does the value for 'x').

I agree that PTAssembler should do something more elegant than crash in this case, but I don't think that there is a "right" way of creating a 360 degree image in stereographic projection (assuming, as PTAssembler does, that the central latitude and central longitude are zero and the image longitude spans from -180 to 180 degrees).

Max

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