Simple Footprint Previewing Specification and Prototype Requirements

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Scope

The scope of this document is to define requirements for displaying simple footprint information for any given observation on the sky. It is assumed, in what follows, that a tool to mark any given position on the sky already exists.

Compliance, Conventions, Definitions

• D1 dataset is a collection of a point in the sky and a unique identifier corresponding to an astronomical observation.
• D2 FoV means field of view.
• D3 compliance document for tabular data is the VOTable Format Specification.
• D4 compliance document for coordinate definition is the Space-Time Coordinate for the Virtual Observatory.

General Capabilities and Needs

• G1 provide a way to display dataset positions on the sky.
• G2 provide a way to specify a list of polygons to display.
• G3 provide a way to correctly project arbitrary polygons on the celestial sphere.
• G4 provide a way to select datasets displayed.
• G5 provide a mechanism to specify a list of dataset positions to display.
• G6 provide a way to associate any given dataset with a given polygon.

Field of View Description

• F1 the geometry of any given FoV must be described by a polygon or a set of polygons (e.g. for mosaic instruments).
• F2 the vertexes of each FoV polygon must be expressed in terms of their distance from the geometrical center coordinate of the FoV.
• F3 the vertexes of each FoV polygon must be expressed in the J2000 equatorial coordinate system.
• F4 The FoV must describe the nominal FoV geometry for the corresponding instrument (and observation mode); without any rotation due to the observation position angle.

Dataset Catalogue

• C1 each dataset entry
  • Must contain its celestial coordinates (RA and Dec).
  • Must contain its identifier.
  • Must contain an instrument identifier.
  • Must contain a FoV identifier.
  • May contain a position angle (in degrees). If not present, the position angle is assumed to be 0 deg.
  • May contain an extra field reserved for rendering purposes (e.g. color).
• C2 all coordinates must be expressed in the J2000 equatorial coordinate system.
• C3 all angles must be in decimal degrees, positive in from North to East.
• C4 the FoV identifier must reference an existing and available FoV description.

Information Transmission

• T1 Both the catalogue and all the FoV descriptions must be written in a single VOTable document.

Rendering

• R1 each FoV must be properly projected onto the sky.
• R2 each FoV must be properly rotated by the corresponding position angle.
• R3 each FoV must be properly shifted by the corresponding offset.
• R4 each dataset position must be properly rendered on the sky.
• R5 users must be able to control the visibility of the FoV polygons:
  • R5a all FoV visible at all times.
  • R5b all FoV invisible at all times.
  • R5c each FoV invisible unless the mouse cursor is over the corresponding dataset marker.

Appendix A

What follows is an example FoV description and dataset catalogue encoded as VOTable Resource elements. As specified above, for the FoV the assumed AstroCoordSystem is simply the standard J2000 equatorial coordinate system. The implied OffsetCenter is the position of the corresponding dataset(s).

<?xml version="1.0"?>
<VOTABLE xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xmlns="http://www.ivoa.net/xml/VOTable/v1.1">
  <DESCRIPTION>Example catalogue and FoV description</DESCRIPTION>
  <RESOURCE>
    <PARAM ID="J2000" name="Coord Frame" datatype="char"
           utype="stc:AstroCoordSys/SpaceFrame/SpaceRefFrame" value="J2000.0"/>
    <DESCRIPTION>Dataset List</DESCRIPTION>
    <TABLE>
     <!-- the three following FIELDS borrow their utype from AstroCoordSys for the FOV -->
      <FIELD name="RA" ucd="pos.eq.ra;meta.main" ref="J2000" datatype="char" arraysize="11"
             unit=""h:m:s"" utype="stc:AstroCoordSys/SpaceFrame/OffsetCenter[1]"/>
      <FIELD name="DEC" ucd="pos.eq.dec;meta.main" ref="J2000" datatype="char" arraysize="11"
             unit=""d:m:s"" utype="stc:AstroCoordSys/SpaceFrame/OffsetCenter[2]"/>
      <FIELD name="PA" ucd="pos.posAng" datatype="float" unit="deg"
             utype="stc:AstroCoordSys/SpaceFrame/PositionAngle"/>
      <FIELD name="DATASET_ID" ucd="meta.id" datatype="char" arraysize="28" />
      <FIELD name="INSTRUMENT" ucd="meta.id;instr" datatype="char" arraysize="13" />
      <!-- The utype of this FIELD means that it contains the id attribute of the -->
      <!-- the spatial (ucd=pos) support of characterization/coverage, which is exactly -->
      <!-- the Field of View -->
      <FIELD name="FoVRef" datatype="char" arraysize="20" utype="ivoa:characterization/[ucd=pos]/coverage/support/@id" />
      <FIELD name="COLOUR" datatype="int" />
      <DATA>
        <TABLEDATA>
          <TR>
            <TD>20:48:16.76</TD>
            <TD>-40:10:35.2</TD>
            <TD>10.5</TD>
            <TD>FORS1.2004-07-23T07:36:08.899</TD>
            <TD>FORS1</TD>
            <TD>FakeInstrFoV</TD>
            <TD>10</TD>
          </TR>
          <TR>
            <TD>20:48:16.10</TD>
            <TD>-40:11:08.8</TD>
            <TD>0.0</TD>
            <TD>FORS1.2004-07-30T08:18:53.053</TD>
            <TD>FORS1</TD>
            <TD>FakeInstrFoV</TD>
            <TD>10</TD>
          </TR>
        </TABLEDATA>
      </DATA>
    </TABLE>
  </RESOURCE>
  <!-- This is the FOV itself (and a utype for that) -->
  <RESOURCE ID="FakeInstrFoV" name ="Fake Instrument Field of View" utype="ivoa:characterization/[ucd=pos]/coverage/support" >
    <DESCRIPTION>Ficticious FoV made up of a two identical rectangle"s
      separated by 5 arcsec. Each rectangle has dimensions 2' x 5'.
    </DESCRIPTION>
    <!-- These two complete the Field of View Coordinate system -->
    <PARAM name="FOV Coord Frame" datatype="char"
            utype="stc:AstroCoordSys/SpaceFrame/SpaceRefFrame" value="J2000.0"/>
    <PARAM name="FOV Coord Flavor" datatype="char"
            utype="stc:AstroCoordSys/SpaceFrame/CoordFlavor" value="CARTESIAN"/>
    <TABLE ID="fovT1" name="Field of View">
      <PARAM name="Region" value="Polygon" />
      <!-- here comes the description of the Vertexes in the tilted and recentered frame -->
      <FIELD ID="VRO" name="VertexRAOffset" datatype="float" unit="arcsec"
          utype="stc:AstroCoordArea/Region/reg:Polygon/Vertex/Position[1]"/>
      <FIELD ID="VDO" name="VertexDecOffset" datatype="float" unit="arcsec"
          utype="stc:AstroCoordArea/Region/reg:Polygon/Vertex/Position[2]"/>
      <DATA>
        <TABLEDATA>
          <TR><TD>-2.5</TD><TD>-150.0</TD></TR>
          <TR><TD>-122.5</TD><TD>-150.0</TD></TR>
          <TR><TD>-122.5</TD><TD>150.0</TD></TR>
          <TR><TD>-2.5</TD><TD>150.0</TD></TR>
        </TABLEDATA>
      </DATA>
    </TABLE>
      <TABLE ID="fovT2" name="Field of View">
      <PARAM name="Region" value="Polygon" />
      <FIELD ref="VRO" />
      <FIELD ref="VDO" />
      <DATA>
        <TABLEDATA>
          <TR><TD>122.5</TD><TD>-150.0</TD></TR>
          <TR><TD>2.5</TD><TD>-150.0</TD></TR>
          <TR><TD>2.5</TD><TD>150.0</TD></TR>
          <TR><TD>122.5</TD><TD>150.0</TD></TR>
        </TABLEDATA>
      </DATA>
    </TABLE>
  </RESOURCE>
</VOTABLE>

Appendix B

Here we describe the field of view using the STC Box structure instead of the Polygon one.

<?xml version="1.0"?>
<VOTABLE xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xmlns="http://www.ivoa.net/xml/VOTable/v1.1">
  <DESCRIPTION>Example catalogue and FoV description</DESCRIPTION>
  <RESOURCE>
    <PARAM ID="J2000" name="Coord Frame" datatype="char"
            utype="stc:AstroCoordSys/SpaceFrame/SpaceRefFrame" value="J2000.0"/>
    <DESCRIPTION>Dataset List</DESCRIPTION>
    <TABLE>
      <!-- the three following FIELDS borrow their utype from AstroCoordSys for the FOV -->
      <FIELD name="RA" ucd="pos.eq.ra;meta.main" ref="J2000" datatype="char" arraysize="11"
             unit=""h:m:s"" utype="stc:AstroCoordSys/SpaceFrame/OffsetCenter[1]"/>
      <FIELD name="DEC" ucd="pos.eq.dec;meta.main" ref="J2000" datatype="char" arraysize="11"
             unit=""d:m:s"" utype="stc:AstroCoordSys/SpaceFrame/OffsetCenter[2]"/>
      <FIELD name="PA" ucd="pos.posAng" datatype="float" unit="deg"
             utype="stc:AstroCoordSys/SpaceFrame/PositionAngle"/>
      <FIELD name="DATASET_ID" ucd="meta.id" datatype="char" arraysize="28" />
      <FIELD name="INSTRUMENT" ucd="meta.id;instr" datatype="char" arraysize="13" />
      <!-- The utype of this FIELD means that it contains the id attribute of the -->
      <!-- the spatial (ucd=pos) support of characterization/coverage, which is exactly -->
      <!-- the Field of View -->
      <FIELD name="FoVRef" datatype="char" arraysize="20" utype="ivoa:characterization/[ucd=pos]/coverage/support/@id" />
      <FIELD name="COLOUR" datatype="int" />
      <DATA>
        <TABLEDATA>
          <TR>
            <TD>20:48:16.76</TD>
            <TD>-40:10:35.2</TD>
            <TD>10.5</TD>
            <TD>FORS1.2004-07-23T07:36:08.899</TD>
            <TD>FORS1</TD>
            <TD>FakeInstrFoV</TD>
            <TD>10</TD>
          </TR>
          <TR>
            <TD>20:48:16.10</TD>
            <TD>-40:11:08.8</TD>
            <TD>0.0</TD>
            <TD>FORS1.2004-07-30T08:18:53.053</TD>
            <TD>FORS1</TD>
            <TD>FakeInstrFoV</TD>
            <TD>10</TD>
          </TR>
        </TABLEDATA>
      </DATA>
    </TABLE>
  </RESOURCE>
  <RESOURCE ID="FakeInstrFoV" name ="Fake Instrument Field of View" utype="ivoa:characterization/[ucd=pos]/coverage/support" >
    <DESCRIPTION>Ficticious FoV made up of a two identical rectangle"s
      separated by 5 arcsec. Each rectangle has dimensions 2' x 5'.
    </DESCRIPTION>
    <!-- These two complete the Field of View Coordinate system -->
    <PARAM name="FOV Coord Frame" datatype="char"
            utype="stc:AstroCoordSys/SpaceFrame/SpaceRefFrame" value="J2000.0"/>
    <PARAM name="FOV Coord Flavor" datatype="char"
            utype="stc:AstroCoordSys/SpaceFrame/CoordFlavor" value="CARTESIAN"/>
    <TABLE ID="fovT1" name="Field of View 1 part">
      <PARAM name="Region" value="Box" />
      <!-- The AstroCoord sys definition allows to define a box with sides parallel -->
      <!-- to the "tilted" axes of the system -->
      <PARAM ID="CRO" name="CenterRAOffset" datatype="float" unit="arcsec"
              utype="stc:AstroCoordArea/Region/reg:Box/Center[1]" value="-62.5"/>
      <PARAM ID="CDO" name="CenterDecOffset" datatype="float" unit="arcsec"
              utype="stc:AstroCoordArea/Region/reg:Box/Center[2]" value="0.0" />
      <PARAM ID="SizRA" name="SizeRA" datatype="float" unit="arcsec"
              utype="stc:AstroCoordArea/Region/reg:Box/Size[1]" value="120.0"/>
      <PARAM ID="SizDE" name="SizeDE" datatype="float" unit="arcsec"
              utype="stc:AstroCoordArea/Region/reg:Box/Size[2]" value="300.0"/>
    </TABLE>
    <TABLE ID="fovT2" name="Field of View 2 part">
      <PARAM name="Region" value="Box" />
      <PARAM ID="CRO" name="CenterRAOffset" datatype="float" unit="arcsec"
              utype="stc:AstroCoordArea/Region/reg:Box/Center[1]" value="62.5"/>
      <PARAM ID="CDO" name="CenterDecOffset" datatype="float" unit="arcsec"
              utype="stc:AstroCoordArea/Region/reg:Box/Center[2]" value="0.0" />
      <PARAM ID="SizRA" name="SizeRA" datatype="float" unit="arcsec"
              utype="stc:AstroCoordArea/Region/reg:Box/Size[1]" value="120.0"/>
      <PARAM ID="SizDE" name="SizeDE" datatype="float" unit="arcsec"
              utype="stc:AstroCoordArea/Region/reg:Box/Size[2]" value="300.0"/>
    </TABLE>
  </RESOURCE>
</VOTABLE>

-- FrancescoPierfederici - 13 Jun 2005