Telescopes in XML part 2
Several weeks ago I mentioned my motivation for a simple telescope XML file and then I came up with a suggested format. Other things got in the way so I haven't really done a lot on this since. However, now seems a suitable time to push this forwards.
I've altered things slightly, taking into account some of the previous suggestions. Below is a table of tags with allowable values. Dave P suggested changing the <coordinates> tag in order to split the latitude and longitude up and provide future proofing for telescope not on the Earth. However, I would prefer to stick with the simple format that Google Earth uses rather than something all-singing and all-dancing like they use for the Virtual Observatory.
| Tag | Type | Notes |
|---|---|---|
| name* | String | Name e.g. <name>42ft</name> |
| desc | String | A short description of the telescope. Limited number of characters? e.g. <desc>The 42ft telescope at Jodrell Bank Observatory</desc> |
| link | URL | Link to a web page with more information about the telescope. e.g. <link>http://www.blah/42ft.html</link> |
| image | URL | An image showing the telescope. In jpg, gif or png formats. e.g. <image>http://www.blah/42.png</image> |
| Point | The latitude/longitude of the telescope. Should be provided where possible, although for some it makes little sense e.g. Hubble. | |
| Point -> coordinates | Coordinates | Same format as used by Google Earth i.e. latitude,longitude. Longitude ranges from 0 to 360 degrees. Latitude ranges from -90 to +90 degrees. A sign should be provided for latitude to avoid confusion. Optional but strongly recommended. e.g. <coordinates>53.235864,-2.306592</coordinates> |
| height | Real number | This is the height above mean sea level in metres. For space-based telescopes this may be omitted. Optional but strongly recommended. e.g. <height>213.1</height> |
| status | String | This is an open format field to provide any status information. e.g. <status>Cryogenic failure, motors stopped.</status> |
| time* | ISO 8601 Date String | Time when the information is this file was valid. e.g. <time>2007-10-14T12:00:00Z</time> |
| object | String | This contains the name of the object. An optional type attribute should be taken from the astronomy journal keyword list. Multiple types can be included using";" or "--" as a separator so that it is consistent with journal papers. e.g. <object type="pulsars: individual: PSR J0534+2200">The Crab Pulsar</object> |
| position | A tag to hold the current coordinates of the observation. The amount of precision in the coordinates is left to the author of the file. This allows for 'fuzzy' positions to be given when required. | |
| position -> ra | Real number | This is the Right Ascension as a single number in decimal degrees. RA in hours, minutes and seconds can be easily calculated. e.g. <ra>123.456</ra> |
| position -> dec | Real number | This is the Declination as a single number. Dec in degrees, arcminutes and arcseconds can be easily calculated. e.g. <dec>+45.678</dec> |
| position -> epoch | String | A standard epoch for the Ra/Dec coordinates such as: B1950, J2000 etc e.g. <epoch>J2000</epoch> |
| position -> az | Real numbers | This is the azimuthal position in decimal degrees (north = 0, east = 90). An optional attribute dem can give the demanded azimuth if it is different to the actual azimuth of the telescope e.g. <az dem="172.34">170.06</az> |
| position -> el | Real numbers | This is the elevation of the telescope in decimal degrees (horizon = 0.0, zenith = 90.0). An optional attribute dem can give the demanded elevation if it is different to the actual elevation of the telescope. e.g. <el dem="34.6">34.567</el> |
* these are required tags
Finally, does anyone have any experience writing DTDs or XML Schema?
Comments: Telescopes in XML part 2
I'd just like to point out that the future-proofing suggestion was at least 1/2 in jest. ;-)
Posted by Dave Pearson on Sunday 14th Oct 2007 (20:24 UTC)
I know, but it would have been nice to have L1, L2 and Mars covered too!
Posted by Stuart on Sunday 14th Oct 2007 (20:25 UTC)
How about also allowing the [current] size of the beam to be provided? Also, the observational frequency/wavelength/energy (and possibly instrument name)? Finally, some way of indicating whether it is working as part of a network ("VLBI"/"MERLIN"/etc.) or as a standalone instrument? All as optional parameters, of course.
By the way, your Preview function here doesn't seem to work; it shows you other people's comments, but not the one that's being written...
Posted by Mike Peel on Monday 15th Oct 2007 (08:33 UTC)
I've had further discussion with Mike and I reckon a "field-of-view" option would be a good idea. That way appropriate sized circles, crosshairs, images could be inserted into something like Google sky to show the area being observed. We decided on field-of-view rather than beam size as it is more general and more understandable to most people.
A wavelength option might be nice but I haven't thought of a good reason for it other than that. I also worry that given the huge range of wavelengths covered in astronomy, using a unit such as metres may run into rounding issues for some scripting languages. If the unit was left open, that would put unnecessary computations on to any parsers that people made and I'm not keen on that.
The indication of being part of a network can be included in the text description so is not really necessary as a separate field within the scope of this idea.
Posted by Stuart on Monday 15th Oct 2007 (17:19 UTC)