Dissemination

As the H-alpha survey is now an official sky survey to be undertaken for the community by the AAO, the digital data will be made available for general access. Some aspects of the data distribution, however, need to be finalised; for example are the pixel data conducive to compression, or is detail lost and the data should be distributed in raw uncompressed form only?

One thing is certain, however, that developments in storage technology will ensure that distribution of the full uncompressed data set is not out of the question. Already, we are seeing the arrival of Digital Video Disks (DVDs) on the scene. At present, these are single-sided, single-layered with a maximum capacity of 4.7 Gbytes. However, the planned development of these is for double-sided, double-layered with 4 times the above capacity. And it is certain that the future of high capacity storage on CD-type technology will not stop there.

At the present time, our planning assumption is that the H-alpha survey in digital form will be available on the higher capacity DVDs. The full survey will, therefore, require 15 such media. If compression were used, then it is envisaged that the entire H-alpha survey of the Galactic Plane and Magellanic Clouds could be made available on typically a single disk.

As well as distributing the pixel data on digital video disk, we plan to allow the pixel data to be accessible via the World Wide Web serviced from the ROE and also the AAO. We have already developed a JAVA-based interface which will allow the user to view areas of survey pixel data, with the coordinate selection driven by the user. The browser allows not only the pixel data to be viewed but also simultaneously the relevant region of the point-source catalogue. Objects can be selected either from the point source database (which will allow the corresponding pixel data to be viewed) or alternatively, given a selection from the pixel data, the corresponding source in the database is highlighted. The DVD version of the database will be distributed with similar access software.

In addition to the above, there are two other plans currently being considered for allowing ease of use of the pixel data. Firstly, we are intending to put the pixel data on the same xy grid system as the J, R and I survey pixel data (with J as 'master'). This will facilitate comparison of the H-alpha data with broadband data in the other passbands, and allow colours to be intercompared. Secondly, we intend to produce "averaged down" versions of the full pixel data for each plate (compressed by a factor of 8 in each dimension) as TIFF files of size 3312 x 3312 pixels. This will allow the data to be easily manipulated in order to aid the construction of mosaics of large regions (or even the whole Southern sky part) of the Milky Way. The TIFF files will be distributed with the full data set, or can be acquired separately as desired.

Our aim is to have the entire database ready for rapid dissemination very shortly after the final photographs have been taken by the UKST (i.e. in about 2-3 years time). However, as there will also be strong interest in selected areas of the Galactic Plane and the Magellanic Clouds, distribution of large, contiguous, high-interest regions of sky will be performed in a timely manner.

© Copyright Astronomical Society of Australia 1997