Extend QuadrupoleKey to celestial coords.

We can thereby use the same underlying mechanism to describe quadrupoles in
pixel and celestial coordinates. Internally, we continue to refer to "x" and
"y", but use appropriate names and units when writing to a table.

include/lsst/afw/table/aggregates.h

@@ -191,25 +191,27 @@ bool operator!=(CoordKey const & lhs, CoordKey const & rhs);
 //@}
 
 /**
- *  @brief A FunctorKey used to get or set a geom::ellipses::Quadrupole from an (xx,yy,xy) tuple of Keys.
+ *  @brief A FunctorKey used to get or set a geom::ellipses::Quadrupole from a tuple of constituent Keys.
  */
 class QuadrupoleKey : public FunctorKey< lsst::afw::geom::ellipses::Quadrupole > {
 public:
 
     /**
-     *  Add a set of _xx, _yy, _xy fields to a Schema, and return a QuadrupoleKey that points to them.
      *
-     *  @param[in,out] schema  Schema to add fields to.
-     *  @param[in]     name    Name prefix for all fields; "_xx", "_yy", "_xy", will be appended to this
-     *                         to form the full field names.
-     *  @param[in]     doc     String used as the documentation for the fields.
-     *  @param[in]     unit    String used as the unit for all fields.
+     *  Add a set of quadrupole subfields to a schema and return a QuadrupoleKey that points to them.
+     *
+     *  @param[in,out] schema     Schema to add fields to.
+     *  @param[in]     name       Name prefix for all fields; ("_xx", "_yy", "_xy") will be appended to
+     *                            this to form the full field names. In celestial coordinates, we use "x"
+     *                            as a synonym for "RA" and "y" for "dec".
+     *  @param[in]     doc        String used as the documentation for the fields.
+     *  @param[in]     coordType  Type of coordinates in use (PIXEL or CELESTIAL).
      */
     static QuadrupoleKey addFields(
         Schema & schema,
         std::string const & name,
         std::string const & doc,
-        std::string const & unit
+        CoordinateType coordType=CoordinateType::PIXEL
     );
 
     /// Default constructor; instance will not be usable unless subsequently assigned to.
@@ -231,15 +233,16 @@ class QuadrupoleKey : public FunctorKey< lsst::afw::geom::ellipses::Quadrupole >
     {}
 
     /**
-     *  @brief Construct from a subschema, assuming xx, yy, and xy subfields
+     *  @brief Construct from a subschema with appropriate subfields
+     *
+     *  If the schema has "a_xx", "a_yy" and "a_xy" fields this constructor enables you to
+     *  construct a QuadrupoleKey via:
      *
-     *  If a schema has "a_xx", "a_yy", and "a_xy" fields, this constructor allows you to construct
-     *  a QuadrupoleKey via:
      *  @code
-     *  QuadrupoleKey k(schema["a"]);
+     *  QuadrupoleKey k(schema["a"], coordType);
      *  @endcode
      */
-    QuadrupoleKey(SubSchema const & s) : _ixx(s["xx"]), _iyy(s["yy"]), _ixy(s["xy"]) {}
+    QuadrupoleKey(SubSchema const & s): _ixx(s["xx"]), _iyy(s["yy"]), _ixy(s["xy"]) {}
 
     /// Get a Quadrupole from the given record
     virtual geom::ellipses::Quadrupole get(BaseRecord const & record) const;

include/lsst/afw/table/misc.h

@@ -20,6 +20,11 @@ namespace lsst { namespace afw { namespace table {
  */
 typedef boost::int64_t RecordId;
 
+enum class CoordinateType {
+    PIXEL,
+    CELESTIAL
+};
+
 //@{
 /**
  *  @brief Tag types used to declare specialized field types.

src/table/aggregates.cc

@@ -94,8 +94,10 @@ QuadrupoleKey QuadrupoleKey::addFields(
     Schema & schema,
     std::string const & name,
     std::string const & doc,
-    std::string const & unit
+    CoordinateType coordType
 ) {
+    std::string unit = coordType == CoordinateType::PIXEL ? "pixels^2" : "radians^2";
+
     Key<double> xxKey = schema.addField<double>(schema.join(name, "xx"), doc, unit);
     Key<double> yyKey = schema.addField<double>(schema.join(name, "yy"), doc, unit);
     Key<double> xyKey = schema.addField<double>(schema.join(name, "xy"), doc, unit);
@@ -120,7 +122,7 @@ EllipseKey EllipseKey::addFields(
     std::string const & doc,
     std::string const & unit
 ) {
-    QuadrupoleKey qKey = QuadrupoleKey::addFields(schema, name, doc, unit + "^2");
+    QuadrupoleKey qKey = QuadrupoleKey::addFields(schema, name, doc, CoordinateType::PIXEL);
     PointKey<double> pKey = PointKey<double>::addFields(schema, name, doc, unit);
     return EllipseKey(qKey, pKey);
 }

tests/testFunctorKeys.py

@@ -154,7 +154,7 @@ def testCoordKey(self):
 
     def testQuadrupoleKey(self):
         schema = lsst.afw.table.Schema();
-        fKey0 = lsst.afw.table.QuadrupoleKey.addFields(schema, "a", "moments", "pixels^2")
+        fKey0 = lsst.afw.table.QuadrupoleKey.addFields(schema, "a", "moments", lsst.afw.table.PIXEL)
         xxKey = schema.find("a_xx").key
         yyKey = schema.find("a_yy").key
         xyKey = schema.find("a_xy").key

tests/testSourceTable.py

@@ -102,7 +102,7 @@ def setUp(self):
         self.centroidFlagKey = self.schema.addField("b_flag", type="Flag")
 
         self.shapeKey = lsst.afw.table.QuadrupoleKey.addFields(self.schema,
-            "c", "", "pixels^2")
+            "c", "", lsst.afw.table.PIXEL)
         self.xxErrKey = self.schema.addField("c_xxSigma", type = "F")
         self.xyErrKey = self.schema.addField("c_xySigma", type = "F")
         self.yyErrKey = self.schema.addField("c_yySigma", type = "F")