GALPHAT hierarchical data structure problem is solved.

Finally I tracked down and solved the problem due to the hierarchical data structure. PSF image should have been shifted by factor of 0.5*(aggpix-1) in case where reference position of pixel coordinate is at the center of pixel. Then this PSF image should be aggregated as I did before. If doing convolution with PSF image which is not offset by this factor, this causes likelihood ratio to be asymmetric and makes the centroid in second level to be diverge.

I have bogged down several times due to “Jean Baptiste Joseph Fourier” but I can’t hate him because, without Fourier transform, I wouldn’t be able to make GALPHAT reasonably fast and feasible to be used in large survey data.

Advertisements

~ by ilsangyoon on July 15, 2008.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

 
%d bloggers like this: