SkyView LogLog scaling

Posted on October 24, 2008 by Tess Jaffe

SDSS Image of 3c273 with standard Log scaling.

SDSS Image of 3c273 with standard log scaling.

SDSS images of 3c273 with LogLog scaling.

SDSS Image of 3C273 with new LogLog scaling.

If you compare an SDSS image versus one for another optical survey like the DSS, there usually appears to be a lot less there. However this is mostly an artifact of the scaling of images. The SDSS images are derived from CCDs rather than photographic plates. You can get something much closer to the plate images if you do a log(log(b)) scaling of the image. Our test version of SkyView now has a loglog scaling option.

We first multiply the each pixel so that that smallest positive value has the value 1.01. Then we take the log of each pixel in that image, Finally we take the log of that result. The ImageJ log function that we use returns a value of 0 for inputs of 0 or less, so those values all end up at 0.

If you want to really bring out detail in the image you’ll soon be able to try scaling=loglog. The two images that start the post show the difference between Log and LogLog scaling. In the loglog image, the jet is plainly visible while it’s completly missing in the first image.

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SkyView Blog Comments Policy

Posted on October 21, 2008 by Tess Jaffe

We welcome comments on any SkyView blog entry. Comments are moderated. Comments whose primary purpose seems to be to link to some other site and are not responsive to the article will be rejected. Please contact us at the regular SkyView mailing address if you feel that a comment has been rejected inappropriately.

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SkyView Gallery Update

Posted on October 21, 2008 by Carina Kan
To make the SkyView Image Gallery easier to navigate (and faster to load) we have split it up into pages with 18 images per page. Navigation links are at the bottom.

Thanks to all of our SkyView users who have contributed!

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New Batch Script

Posted on October 15, 2008 by Carina Kan

For years we have provided two scripts (skvbatch and webquery) that can be used together to run batch SkyView queries. Recently users have had problems using the scripts due to local firewall issues so we are providing a new script (skvbatch_wget) that uses the GNU utility wget and should work behind firewalls. For more information please visit our Batch Page.

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Full GALEX GR4 Available in SkyView

Posted on October 14, 2008 by Tess Jaffe

The operational version of SkyView now supports the full GALEX GR4 release. This includes a total of about 170,000 UV images of the sky. Total coverage is about 25,000 square degrees or well over half the sky.

As discussed in earlier posts, GALEX uses a slightly different method of image selection than most other surveys. For a given output pixel, we find the input image which is within a cutoff radius and has the largest exposure. Thus where there are both survey pointed GALEX observations, the pointed data should be used but the output should transition to survey coverage outside the region of pointed coverage. It’s usually easy to see these transitions since the survey data is significantly noisier (due to the shorter exposures).

We’re cleaning out the GALEX cache in SkyView, so you may see a slight decrease in performance as SkyView extracts files from the MAST archive that were already in our cache.

One consequence of this release is that the SkyView jar has gained a little weight — it’s now about 17 MB. Almost all of that is survey descriptions and survey data. Ultimately we may need to separate the code and survey documents into separate files.

The Java 1.5 compatible jar has also been updated to the same version. Previously this had still been pointing to SkyView release 2.4.

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New SkyView Image Gallery

Posted on October 7, 2008 by Carina Kan

We have added an Image Gallery to the site and we welcome your SkyView images. Just click the Add to Gallery button below your generated images and they will be added to the gallery and included in the pool of images that are randomly displayed on the main SkyView page. The button will appear if your image is below a set size limit. Images will stay in the Image Gallery until we start running out of storage space at which time we will remove older images.

So if you have created a image that you would like to share please do so! And let us know if you have any questions or comments.

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GALEX GR4 data temporarily unavailable

Posted on August 20, 2008 by Carina Kan

GALEX UV survey GR4 images may not be available at this time due to hardware failure at the remote MAST site. The most recent notice on the MAST website indicates data will not be available until the week of 8/25/08 at the earliest.

SkyView saves images from remote survey queries so GALEX image generation at many positions may still be possible.

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SkyView Temporarily Unavailable August 18, 2008

Posted on August 20, 2008 by Carina Kan

SkyView operations were interrupted Monday afternoon August 18, 2008 due to a local network problem. The website was unavailable from approximately 4:00-8:00pm EST. We apologize for the inconvenience.

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FIRST update

Posted on August 12, 2008 by Carina Kan

We have completed changes to SkyView to accommodate FIRST data changes at the MAST archive. FIRST data file names have changed and files for additional coverage have been added. Both the SkyView web site and SkyView-in-a-Jar file have been updated.

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New plot overlay capability

Posted on August 1, 2008 by Tess Jaffe

The latest version of SkyView has a new capability for drawing overlays on SkyView images. One major use of this will be to allow us to provide templates of the fields of view of various telescopes. E.g., in the image below we’ve overlaid information on the fields of view of two of the instruments of the Swift observatory on a simple DSS image of the region around 3c273. The X-ray Telescope (XRT) field of view has calibration sources (C1-4) marked in the corners, while the UltraViolet-Optical Telescope (UVOT) has a large rotation (and small offset) with respect to the satellite’s nominal pointing.

XRT and UVOT Fields of View over 3c273

The overlays use simple ‘Draw’ files that describe the fields of view. E.g., the draw file for the XRT part of the overlay above is just:

reset
scale 2.36"

thick 2
color cyan

-300 -301
300 -301
300 301
-300 301
-300 -301

text 0 270 0 XRT FOV
text 0 -290 0 XRT FOV
text 290 0 90 XRT FOV
text -270 0 90 XRT FOV

thick 1
color pink
circle -265 269 47
circle 273 260 48
circle -264 -274 47
circle 276 -281 44

text -265 269 0 C0
text 273 260 0 C1
text -264 -274 0 C2
text 276 -281 0 C3

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