Slew to the coordinates that put the spec target on fibre

sdss · Jul 12, 2023 · afab2bf · afab2bf
1 parent b4b9b23
commit afab2bf
Showing 1 changed file with 16 additions and 6 deletions.
diff --git a/src/gort/observer.py b/src/gort/observer.py
@@ -17,6 +17,7 @@
 
 from gort.exceptions import GortObserverError
 from gort.tools import register_observation
+from gort.transforms import fibre_slew_coordinates
 
 
 if TYPE_CHECKING:
@@ -65,7 +66,10 @@ async def slew(self):
 
         spec = None
         if self.tile.spec_coords and len(self.tile.spec_coords) > 0:
-            spec = (self.tile.spec_coords[0].ra, self.tile.spec_coords[0].dec)
+            # For spec we slew to the fibre with which we'll observe first.
+            # This should save a bit of time converging.
+            spec_target = (self.tile.spec_coords[0].ra, self.tile.spec_coords[0].dec)
+            spec = fibre_slew_coordinates(*spec_target, self.mask_positions[0])
             self.write_to_log(f"Spec: {self.tile.spec_coords[0]}")
 
         sky = {}
@@ -378,12 +382,18 @@ async def _iterate_over_mask_positions(self, exposure_time: float):
                 # Moving the mask to an intermediate position while we move around.
                 await spec_tel.fibsel.move_relative(500)
 
-                # Slew to new coordinates.
-                # TODO: to speed up acquisition we should slew to the coordinates
-                # of the fibre, or do an offset just before beginning to guide.
-                await spec_tel.goto_coordinates(ra=new_coords.ra, dec=new_coords.dec)
+                # Slew to new coordinates. We actually slew to the coordinates
+                # that make the new star close to the fibre that will observe it.
+                slew_ra, slew_dec = fibre_slew_coordinates(
+                    new_coords.ra,
+                    new_coords.dec,
+                    new_mask_position,
+                )
+                await spec_tel.goto_coordinates(ra=slew_ra, dec=slew_dec)
 
-                # Start to guide.
+                # Start to guide. Note that here we use the original coordinates
+                # of the star along with the pixel on the master frame on which to
+                # guide. See the note in fibre_slew_coordinates().
                 self.write_to_log("Starting to guide on spec telescope.")
                 await self.gort.guiders.spec.guide(
                     ra=new_coords.ra,