|
88 | 88 | coordinate range |
89 | 89 | </entry> |
90 | 90 | </row> |
| 91 | + <row> |
| 92 | + <entry> |
| 93 | + <type>smoc</type> |
| 94 | + </entry> |
| 95 | + <entry> |
| 96 | + HEALPix Multi-Order Coverage map |
| 97 | + </entry> |
| 98 | + </row> |
91 | 99 | </tbody> |
92 | 100 | </tgroup> |
93 | 101 | </table> |
@@ -682,4 +690,62 @@ i syntax is a somewhat complex. |
682 | 690 | </programlisting> |
683 | 691 | </example> |
684 | 692 | </sect2> |
| 693 | + |
| 694 | + <sect2 id="dt.smoc"> |
| 695 | + <title> |
| 696 | + HEALPix Multi-Order Coverage map |
| 697 | + </title> |
| 698 | + <para> |
| 699 | + <mediaobject> |
| 700 | + <imageobject> |
| 701 | + <imagedata fileref="&graphsmoc;" width="287px" format="PNG"/> |
| 702 | + </imageobject> |
| 703 | + </mediaobject> |
| 704 | + </para> |
| 705 | + <para> |
| 706 | + The datatype smoc allows one to define and manipulate any region |
| 707 | + of the sky in such a way that basic operations like union, |
| 708 | + intersection can be performed very efficiently. It is dedicated to |
| 709 | + VO applications or VO data servers for building efficient |
| 710 | + procedures for which mapping knowledge is required like generic |
| 711 | + catalog cross-match, computation of data set intersections, etc. |
| 712 | + This encoding method is called "Multi-Order Coverage map" or "MOC". |
| 713 | + </para> |
| 714 | + <para> |
| 715 | + The goal behind the MOC is to get a spherical geometry description |
| 716 | + for any sky region in order to provide very fast and accurate |
| 717 | + union, intersection and equality operations between them. In order |
| 718 | + to accomplish this task, we based the system on a regular and |
| 719 | + hierarchical partitioning of the sphere, a process called |
| 720 | + tessellation. |
| 721 | + </para> |
| 722 | + <para> |
| 723 | + The MOC standard is described at http://www.ivoa.net/documents/MOC/ |
| 724 | + </para> |
| 725 | + <synopsis>level/pixel1-pixel2 [...] level/pixel1-pixel2 [...]</synopsis> |
| 726 | + <example> |
| 727 | + <title> |
| 728 | + The empty set |
| 729 | + </title> |
| 730 | + <programlisting> |
| 731 | +<![CDATA[sql> SELECT smoc '0/';]]> |
| 732 | + </programlisting> |
| 733 | + </example> |
| 734 | + <example> |
| 735 | + <title> |
| 736 | + The whole sky |
| 737 | + </title> |
| 738 | + <programlisting> |
| 739 | +<![CDATA[sql> SELECT smoc '0/0-11';]]> |
| 740 | + </programlisting> |
| 741 | + </example> |
| 742 | + <example> |
| 743 | + <title> |
| 744 | + A disk around the point (0, 0) with radius 1 at MOC level 2 |
| 745 | + </title> |
| 746 | + <programlisting> |
| 747 | +<![CDATA[sql> SELECT smoc '0/4 1/0 2 12-13 34-35 45 47 2/4 6 12 14 56-57 60-61 88 90-91 116-117 119 130-131 134-135 177 179 185 187';]]> |
| 748 | + </programlisting> |
| 749 | + </example> |
| 750 | + </sect2> |
685 | 751 | </sect1> |