Re: Accesing to Measurements from a Macro

Posted by Alnair on Dec 30, 2014; 1:24pm
URL: http://astroimagej.170.s1.nabble.com/Accesing-to-Measurements-from-a-Macro-tp211p217.html

Hi Karen,

Including the function in Java like you describe would be great. Thanks.

The "T5" solution could work (and be very practical) for some cases, were object movement is slow and the field is not very crowded of stars.

Objects can move from less than 1 pixel from image to image to a large extend of the field for near earth asteroids.

The number of images in a time series can vary a lot. From 3 to 10 are the usual for astrometric purposes which can include

photometric measures. But for minor planet rotation detection, it can fall in the order of hundreds (1 image every 1-2 minutes during 3-8 hours).

We can take advantage than objects move at uniform speed and in straight line (during a single observing session) so a very convenient way to handle

this would be to mark object position in the first and the last image and recalculate the position in the rest of images taking into account the hour of each image.

Regards,

  Ferran

2014-12-30 13:40 GMT+01:00 karenacollins [via AstroImageJ] <[hidden email]>:

Hi Ferran,

How much change in position is there typically from one image to the
next for the minor planets and comets? Also, how many images are
typically in the time series when you are following minor planets or
comets? There is probably no concrete answer for either of these
questions, but I am just trying to get a feel for the best way to
address the minor planets and comet photometry issue.

The centroid function works off of the fixed aperture size, even in
variable aperture mode. So, for instance, if you can make the fixed
aperture radius large enough to encompass the change in the moving
target from frame to frame, I think one solution would be to use a
larger fixed aperture radius, and enable variable aperture to shrink the
aperture radius to some factor times the fwhm of the image for the
photometry measurement. For this idea to work the best, you should make
your target star something other than T1, since T1 is used to help find
the relative offsets of all the other target/comp stars from image to
image. As an example, create a C1 (by holding shift when clicking near
the first star), C2 (no shift), C3, C4, and then T5 (by holding shift
when clicking near the target star). Then if T5 doesn't move by more
then the fixed aperture radius from image to image, the centroid feature
should automatically track the moving target while keeping the other
apertures fixed.

That is just one idea. I'll decide on the best solution once I get your
response to the above questions. I'm also considering how to include the
macro you wrote. If I can find time, I'll translate it into java and
include the function as a menu item under the Multi-plot main 'File'
menu (it is harder to add it to the table 'File' menu). Then I can
search for all open tables and automatically select the first one found
(with the option to select another one, if more than one table is open).

Karen

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