User manual

GZIP Compression

Can be used with any other

formats

Aladin recognizes automatically the data type by analyzing the data content. The file

name extension or the “Content-type” definition for an http stream is not required.

Exception : the AJS format (Aladin script) is an exception of this rule. In case of

ambiguity, Aladin will look for an “.ajs” file name extension and/or on this first line

comment “#AJS”.

8.3FITS standard and astrometrical calibration

About astrometrical calibration, Aladin follows the official standard FITS: the first

bottom left pixel has the coordinates (1,1) and the corresponding celestial position is

centered is the middle of this pixel. Concretely, the coordinates for the first pixel are

(0.5,0.5).

Note : IDL does not follow the official FITS standard. It considers (0,0) as the

coordinates of the first pixel.

Aladin recognizes several calibration methods: classical WCS keywords, old DSS1

standard. It supports most of usual projections.

8.4Performances and technical constraints

The Aladin development tried to answer these two points:

1. Provide the best compatibility with the existing hardware and Operating Systems,

2. Provide the best performances in this context.

For answering these two constraints, Aladin has been developed in Java language. The

Java software required a “java runtime environment” installed on the user machine. It is

generally the case for most of Operating Systems. However it is possible to install one

from this address: http://www.java.com/download. It is free and easy.

In the bottom right corner of the main Aladin window some figures are indicating the

current memory usage. The tooltip appearing by moving the mouse over these numbers

provides more details, and notably the maximum memory reserved for Aladin. This limit

can be increased, but only before launching Aladin. For this, have a look in the relevant

FAQ section: (http://aladin.u-strasbg.fr/java/FAQ.htx#huge).

8.4.1 Image management

Aladin is able to manage any size of image. Following your hardware configuration and

the memory reserved for the java run time machine, Aladin will choose the best strategy

amongst these three modes:

 For images having a few megabytes, the image is totally loaded in memory;