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The TERAPIX FAQ
Last content update November 28th, 2006

The Terapix FAQ


General questions about TERAPIX

1. What is Terapix?

2. But what do you do exactly?

TERAPIX and PI data

3. Help! I have 10Tb of MEGACAM/WIRCAM data, how do I reduce it?

4. My PI-mode run has just been executed at CFHT, can I get my data?

5. Where can I retrieve TERAPIX products?

TERAPIX and the official CFHTLS releases

6. What is the current status of the CFHTLS? Where can I retrieve CFHTLS data?

7. What is the difference between a 'release candidate' and a real release? Can I do science with a 'release candidate'?

8. Help! I want to access the terapix release meta-data information, but when I click on the link I'm asked for a password!

9. What are these funny ".fz" files?

10. What are these funny ".ldac" files?

Other questions

11. You still haven't answered my question, who can I contact?

12. How does one acknowledge Terapix?


General questions about TERAPIX

1. What is Terapix?

Terapix is a data reduction centre located at the Institut d'Astrophysique in the beautiful city of Paris, France. The Terapix facility has been designed to handle data flows from mosaic array cameras, with particular emphasis on the MEGACAM and WIRCAM wide-field cameras on CFHT. It is the responsibility of Terapix to provide data processing and support facilities for users of these instruments. TERAPIX software has been successfully used to reduce data from a wide variety of other instruments.

2. But what do you do exactly?

We provide coadded, astrometrically calibrated images, weight (coverage) maps and object catalogues from pre-reduced imaging data, from wide-format cameras at CFHT like MEGACAM and WIRCAM. We also provide software to reduce and visualise this kind of data, which is freely available from our web site.

In detail: starting from the flat-fielded, bias subtracted data, the Terapix pipeline ('Spica') computes astrometric solutions and flux scaling for each input images using TERAPIX software tools. Using these solutions, a single coadded image is created comprising all input images. Then catalogue extraction software (like Sextractor) is used to produce final catalogues, which are then distributed to the community. Note that the pre-reduced data is provided to us by the Elixir pipeline at CFHT; Terapix does not carry out this step.

TERAPIX and PI data

3. Help! I have 10Tb of MEGACAM/WIRCAM data, can you help me to reduce it?

You bet! The exact procedure depends on what data you have (MEGACAM or WIRCAM) and if it is less than one year after the data has been taken or not.

In all emails please state clearly (preferably in the subject line of your message) the RUNID and PI of your dataset.

During the processing, all communication will be done by email directly with the personn in charge of the proocessing, with CC's to mellier@iap.fr for all.

You should first read this article .

For MEGACAM data:

-  If your data are still proprietary (i.e., they were acquired less than one year ago), you must send an email to Kanoa Wilkinson at CFHT (kanoa@cfht.hawaii.edu) and CC Frederic Magnard (magnard@iap.fr) and Yannick Mellier (mellier@iap.fr).

CFHT will then allow TERAPIX to access your data, and it will be transferred to TERAPIX for processing.

-  If you data are no longer in the proprietary period, (taken more than one year ago) you must send and email to CADC where data are archived to inform them that terapix will retrieve your data. A copy of the email must be send to Kanoa Withington at CFHT (kanoa@cfht.hawaii.edu) who will check that your data has been preprocessed; You should also contact Frederic Magnard (magnard@iap.fr) and Yannick Mellier (mellier@iap.fr) at TERAPIX.

WIRCAM data

Here the procedure is slightly different.

-  if your data are still proprietary (they were taken less than one year ago), you must send an email to Loic Albert at CFHT (albert@cfht.hawaii.edu) with a copy to Chiara Marmo (marmo@iap.fr) and Yannick Mellier (mellier@iap.fr). Loic Albert will then allow TERAPIX to retrieve your dataset from CFHT.

-  if you data are no longer in the proprietary period, you must send and email to CADC where your data are archived and to allow TERAPIX to retrieve them. A copy of this mail must be send to Loic Albert at CFHT (albert@cfht.hawaii.edu) with copy to Chiara Marmo (marmo@iap.fr) and Yannick Mellier (mellier@iap.fr).

Finally, if you are really ambitious, you can download the TERAPIX software packages and install each package locally on your machine, and process the data at your home institute. Of course this assumes that you have enough disk space and computing resources to carry this out.

4. My PI-mode run has just been executed at CFHT, can I get my data?

Not directly from us. The CADC is the distribution point for al Megacam images. See the question above.

5. Where can I retrieve TERAPIX products?

When we finish to process your data we put them on TERAPIX ftp site and we send to you the login and password you have to use for the download. Your data will be available on TERAPIX ftp site for one year after they have been released. After one year they will be removed from our disks together with intermediate products of image processing.

TERAPIX and the official CFHTLS releases

6. What is the current status of the CFHTLS? Where is the CFHTLS data?

Please see the CFHTLS web pages at CFHT for the current status of the survey. Note that (as we mentioned above) Terapix does not distribute CFHTLS data, either images or catalogues; the CADC should be your point of reference for this. The CADC CFHTLS community page page provides information about public releases of CFHTLS data. The TERAPIX web pages provide metadata information about the release, such as colour-colour plots and information about the content of the catalogues.

7. What is the difference between a 'release candidate' and a real release? Can I do science with a 'release candidate'?

The release candidates are almost identical to the 'real' release. They are provided on a 'best efforts' basis to the community so that people can start doing science immediately. Some information may be missing, or the data format may not correspond exactly that specified in the official documentation. There may be errors! But in general we have found that the release candidates do correspond very closely to the offical release. You can most certainly do science with the release candidates.

8. Help! I want to access the terapix release meta-data information, but when I click on the link I'm asked for a password!

Just send an email to terapix@iap.fr and we will send you the password.

9. What are these funny ".fz" files?

The are rice-compressed images. All FITS images have been compressed using Rice compression with the tool imcopy from the cfitsio package . For more information see the README file provided with our releases.

10. What are these funny ".ldac" files?

There are simply FITS binary tables. They can be read using tools like 'fv', which also allows you to convert selected columns to plain text. Be careful, though, because 'fv' does not handle correctly vector quantites (such as a MAG_APER which has multiple apertures); in these cases only the first vector is output. A stand-alone TERAPIX tool will be released shortly to convert between binary and ascii catalogue formats and which preserves all vector information.

Other questions

11. You still haven't answered my question, who can I contact?

General enquiries involving Terapix should be sent to terapix@iap.fr. For specific questions relating to software we provide, please post your questions on our forums: terapix.iap.fr/forums; we try to answer questions posted there in one or two working days.

12. How do you ackowledge Terapix?

-  If your work uses data processed by Terapix but which are not CFHTLS data, then please add the following:

"This work is based (in part) on data products produced at the TERAPIX data center located at the Institut d'Astrophysique de Paris."

"in part" should be added, of course, if you have used other data products in your paper apart from those produced at TERAPIX.

-  If you use CFHTLS data, then please add the following:

Asterisk by the author's name to refer to a footnote stating: *Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at TERAPIX and the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS.

13. What coffee do you drink at TERAPIX?

We like 'Caffe 14 Luglio' a lot!


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