Re: Best way to do 400+ stars on three images
Posted by
karenacollins on
Jun 20, 2013; 9:38pm
URL: http://astroimagej.170.s1.nabble.com/Best-way-to-do-400-stars-on-three-images-tp48p49.html
Hi David,
The most straight-forward solution with the current feature set
is to set up the apertures in one of the images by clicking on all
400 stars using Multi-Aperture (remember which star you click first,
you will need it below). Once you have ran Multi-Aperture on that
image, use the menus above the image to save the apertures
(File->Save Apertures). You can now reload the apertures at any
time by going to File->Open Apertures or by simply dragging and
dropping the aperture file onto an image (filename must end in
.aperture for the drag and drop to work). If you don't define new
apertures in a second run of Multi-Aperture, the 400 apertures will
be retained and restored automatically from one AIJ session to the
next (but I would save them as described above in case something
goes wrong or for future use).
To use the previously entered (or reopened) apertures for another
image, even if the images are not aligned, open the 2nd image, start
another Multi-Aperture session, but enable the option "Use previous
X apertures (1-click to set first aperture)" near the top of the
Multi-Aperture set-up panel. You may change the aperture radius and
other setting as needed, but the aperture locations will not be
affected. Then click "OK" and then left-click on the first star that
you clicked when first defining the 400 apertures. When you click on
the first star, all 400 apertures will be placed with the same
relative x,y pixel spacing from the first star as in the first
image. This will work as long as there is no significant image
rotation between the two images. If you prefer to load all three
images in a stack, in the Multi-aperture setup panel, enable the
option "Use single step mode..." near the top. This will allow you
to click on the location of the first star in the aperture list for
every image in the stack. Make sure you have "Show help panel during
aperture selection" enabled to guide you through the single step
process (a series of left and right mouse clicks).
If you are truly resistant to clicking on the 400 stars one
time, John Kielkopf has a utility (Python based I think) that will
convert RA and DEC coordinates to x,y coordinates for images with
WCS coordinates. It would require a little programming work to
format the output from the utility to be compatible with the AIJ
text-file-based .apertures file, but I think it would be fairly
straight forward since the AIJ .apertures file format is very easy
to determine by looking at a sample apertures file saved from AIJ.
It doesn't help you much right now, but I will be adding the
ability to open a list of apertures in RA,DEC file format in the
next few months, but I don't have the bandwidth to add that feature
right now.
Karen
On 6/20/2013 3:59 PM, David Emory [via
AstroImageJ] wrote:
Background: I have 400+ target stars on which I need
to do photometry. I have three images in different colors. I also
have the WCS coordinates in RA and Dec for the target stars in a
text file.
What is the most efficient method to accomplish this? Can
AstroImageJ read in a coordinate text file and then do the
photometry on each image (either individually or as a group)?
If this this not possible, can I select the stars on the first
image and then "tell" AstroImageJ to use the same stars on the
other two images. I tried this with the "Multiple Aperture" option
but it appears that default is to match the second and third
images to the X,Y coordinates and not the WCS. The WCS do not
match the X,Y coordinates as I go from one image to another.