On Wed, 2006-10-11 at 20:14 -0600, zowie wrote:
> On Oct 11, 2006, at 2:15 PM, Rahman Amanullah wrote:
> > Hello!
> >
> > I would imagine that the output PDL from this code ($o) would be
> > identical to the input ($i):
> >
> > use PDL;
> > use PDL::Transform;
> > my $i = sequence(5,5) + sequence(5,5)->transpose;
> > my $o = $i->map(t_identity,
> > {pix=>1,phot=>'flux',method=>'sample'});
>
> Drat, drat, drat -- it appears to be a half-pixel error in the pix=>1
> code. (if you use 'linear' as a method, you can see that the
> sampling is happening at pixel intersections rather than centers).
> I'll check-in a fix into the CVS soon.
Thanks! This seems to be working now!
> By the way, "phot=>'flux'" won't actually do anything unless you are
> using the Gaussian or Hanning methods. That's because flux
> conservation works by measuring the determinant of the Jacobian of
> the transformation, and only the Gaussian and Hanning methods bother
> to find the Jacobian.
I am probably still misunderstanding something. I tried to do the
following:
my $i = sequence(100,100) + sequence(100,100)->transpose;
$i /= $i->sum;
my $ts = t_linear(Scale=>1/10);
my $o = $ts->map($i,{pix=>1,phot=>1,method=>'j'});
print $i->sum, "\n";
print $o->sum, "\n";
For "method=>'j'" and "method=>'g'" I get
Use of uninitialized value in numeric lt (<)
at /usr/local/lib/perl5/site_perl/5.8.8/i686-linux/PDL/Core.pm line
1972, <DATA> line 387.
Use of uninitialized value in subroutine entry
at /usr/local/lib/perl5/site_perl/5.8.8/i686-linux/PDL/Core.pm line
1974, <DATA> line 387.
1
1.57143060984982
A increase with 57%!!!
With "method=>'h'" I get a 22% increase. Perhaps the error message is
the reason for this?
I am using the latest CVS version of PDL.
--
__________________________________________________________
Rahman Amanullah, +46 8 553 786 61
Stockholm University ICQ: 62860758
Stockholm Centre for Physics, 17d 50m E
Astronomy & Biotechnology 59d 26m N
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