[vtk-developers] Re: CVS Write access ? : Possible mistake in vtkRenderLargeImage

[Will Schroeder]

John-

When we do releases we turn off write access for everybody except for 
the one or two people putting in patches, etc. After we give access 
back when requested. This is done as a "self-pruning" mechanism (a 
lot of people go away and never ask for access back). I'll take your 
email as a request and restore access....give us a day or two a lot 
of us are scattered around the country travelling.

Will

At 11:40 AM 11/16/2005, John Biddiscombe wrote:
>I seem to have lost my write access to vtk. I've already committed a 
>fix to the test image (which worked on VTKData), but I'm unable to 
>commit a fix to vtk itself. Is there any reason why I shouldn't be 
>putting in fixes. I wasn't aware of a freeze on at the moment - if 
>not, may I have write access back. Thanks
>
>JB
>
>>Michael
>>
>>I just did the sums and got the same equation as you for the 
>>adjustment to the view angle. Since I recently did some work on 
>>this class, I'll check in your fix.
>>
>>Thanks. (I'd noticed a difference in appearance but hadn't given it 
>>any thought...good spot!)
>>
>>JB
>>
>>>Dear VTK developer community,
>>>
>>>I have come across what I believe to be a mistake in the
>>>implementation of the class vtkRenderLargeImage in the Hybrid
>>>package.  To illustrate the case, please consider the simple VTK
>>>script found at 
>>>http://www.science.uva.nl/~mscarpa/vtk/TestImage.py.   This script 
>>>generates an image as http://www.science.uva.nl/~mscarpa/ vtk/Image.png.
>>>
>>>Now, consider a modified version of the above script as found at
>>>http://www.science.uva.nl/~mscarpa/vtk/TestRenderLargeImage.py.  The
>>>only
>>>differences with the first script are that the render window has
>>>smaller dimensions (a quarter width and a quarter height), and that
>>>it uses the vtkRenderLargeImage class to generate an image of the
>>>same size as the first script (500 by 500 pixels).  This script is
>>>based on the example found with the VTK source code.  On my VTK
>>>installation, the latter script generates an image as http:// 
>>>www.science.uva.nl/~mscarpa/vtk/RenderLargeImageOriginal.png.  This
>>>is considerably different from the expected result, which (in this
>>>simple case) should be identical to the first image.  I have looked
>>>into the code of vtkRenderLargeImage (as can be found in CVS as of
>>>this writing), and I think I
>>>found a mistake.  In the method vtkRenderLargeImage::RequestData(),
>>>the following statement calculates the view angle incorrectly:
>>>
>>> 
>>>cam->SetViewAngle(asin(sin(viewAngle*3.1415926/360.0)/this- >Magnification)
>>>                     * 360.0 / 3.1415926);
>>>
>>>I believe that the correct statement should be as follows:
>>>
>>> 
>>>cam->SetViewAngle(atan(tan(viewAngle*3.1415926/360.0)/this- >Magnification)
>>>                     * 360.0 / 3.1415926);
>>>
>>>The only difference consists in replacing the sine and arcsine
>>>functions with tangent and arctangent functions.  If the class is
>>>recompiled with these changes, the two scripts above produce
>>>identical images (see the image produced by the second script on my
>>>VTK installation after applying the above changes at http:// 
>>>www.science.uva.nl/~mscarpa/vtk/RenderLargeImageModified.png).
>>>
>>>Please note that more complex scenes will not produce absolutely
>>>identical images, but at least the images will be almost identical
>>>and not differ so much due to different view angles.
>>>
>>>For convenience, this text can be found as HTML page at the 
>>>following  location: http://www.science.uva.nl/~mscarpa/vtk/index.html
>>>
>>>Could someone please verify these findings and, if confirmed, could
>>>these changes be taken over in the CVS repository?  Any comment is
>>>obviously most welcome.
>>>
>>>Kind regards,
>>>
>>>Michael Scarpa
>>>Section Computational Science
>>>Universiteit van Amsterdam
>>>Kruislaan 403
>>>1098 SJ Amsterdam, The Netherlands
>>>Room F2.15
>>>Tel: +31 20 525 7574
>>>Fax: +31 20 525 7419
>>>Web: http://www.science.uva.nl/~mscarpa/
>>>
>>>_______________________________________________
>>>vtk-developers mailing list
>>>vtk-developers at vtk.org
>>>http://www.vtk.org/mailman/listinfo/vtk-developers
>>
>>
>>
>
>
>--
>John Biddiscombe,                            email:biddisco @ cscs.ch
>http://www.cscs.ch/about/BJohn.php
>CSCS, Swiss National Supercomputing Centre  | Tel:  +41 (91) 610.82.07
>Via Cantonale, 6928 Manno, Switzerland      | Fax:  +41 (91) 610.82.82
>
>
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