let is_volume be configurable in detect spots methods (#686)

starfish/spots/_detector/detect.py

@@ -164,6 +164,7 @@ def detect_spots(
         reference_image_from_max_projection: bool=False,
         measurement_function: Callable[[Sequence], Number]=np.max,
         radius_is_gyration: bool=False,
+        is_volume: bool=True
 ) -> IntensityTable:
     """Apply a spot_finding_method to a ImageStack
 
@@ -189,6 +190,8 @@ def detect_spots(
         spot intensity, but typically is a smaller unit than the sigma generated by blob_log.
         In this case, the spot's bounding box is rounded up instead of down when measuring
         intensity. (default False)
+    is_volume: bool
+        (default True) If True, pass 3d volumes (x, y, z) to func, else pass 2d tiles (x, y) to func
 
     Notes
     -----
@@ -217,6 +220,11 @@ def detect_spots(
     if reference_image_from_max_projection:
         reference_image = data_stack.max_proj(Indices.CH, Indices.ROUND)
 
+    if is_volume:
+        split_by = {Indices.Z.value, Indices.Y.value, Indices.X.value}
+    else:
+        split_by = {Indices.Y.value, Indices.X.value}
+
     if reference_image is not None:
         reference_spot_locations = spot_finding_method(reference_image, **spot_finding_kwargs)
         intensity_table = measure_spot_intensities(
@@ -229,8 +237,7 @@ def detect_spots(
         spot_finding_method = partial(spot_finding_method, **spot_finding_kwargs)
         spot_attributes_list = data_stack.transform(
             func=spot_finding_method,
-            # always use volumetric or pseudo-3d (1, n, m) data
-            split_by={Indices.Z.value, Indices.Y.value, Indices.X.value}
+            split_by=split_by
         )
         intensity_table = concatenate_spot_attributes_to_intensities(spot_attributes_list)