[Chimera-users] Laplacian filter on density maps

Tom Goddard goddard at cgl.ucsf.edu
Fri Nov 21 15:28:15 PST 2008

Hi Greg,

  I've added volume Laplacian calculation to Chimera.  It is available 
via the volume operation "vop" command.  To calculate the Laplacian of 
model #3 use

    vop #3 laplacian

It will create a new volume data set.  This will be in tonight's Chimera 
1.4 daily builds.



Tom Goddard wrote:
> Hi Greg,
>   A Laplacian filter is simple to implement.  I'll see if I can add it 
> to the "vop" command later this week.  The Laplacian filter roughly 
> speaking does edge detection so alignments of filtered maps will try to 
> match the boundaries of the objects.  The Laplacian is a sum of second 
> derivatives and will be useless on noisy data (e.g. any tomography) 
> unless you smooth the data first with for instance a Gaussian filter.
>     Tom
> Grigore Pintilie wrote:
>> Hi,
>> Just wondering if it might be possible to apply a Laplacian filter on
>> a density map in chimera. The reason I'm asking is that if the
>> cross-correlation is computed with laplacian-filtered maps it gives
>> more robust results for the correct alignments vs. non-correct
>> alignments.
>> Thanks,
>> Greg

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