Document clarification for different representation for bounding box …

…between Turi Create and Vision (#2320)

src/python/turicreate/data_structures/sframe.py

@@ -2660,7 +2660,6 @@ def sample(self, fraction, seed=None, exact=False):
         if (fraction > 1 or fraction < 0):
             raise ValueError('Invalid sampling rate: ' + str(fraction))
 
-
         if (self.num_rows() == 0 or self.num_columns() == 0):
             return self
         else:
@@ -2709,6 +2708,7 @@ def random_split(self, fraction, seed=None, exact=False):
         """
         if (fraction > 1 or fraction < 0):
             raise ValueError('Invalid sampling rate: ' + str(fraction))
+
         if (self.num_rows() == 0 or self.num_columns() == 0):
             return (SFrame(), SFrame())
 

userguide/object_detection/export-coreml.md

@@ -24,7 +24,7 @@ let objectRecognition = VNCoreMLRequest(model: visionModel,
 
     for case let foundObject as VNRecognizedObjectObservation in results {
         let bestLabel = foundObject.labels.first! // Label with highest confidence
-        let objectBounds = foundObject.boundingBox
+        let objectBounds = foundObject.boundingBox // Normalized between [0,1]
 
         // Use the computed values.
         print(bestLabel.identifier, bestLabel.confidence, objectBounds)
@@ -37,6 +37,8 @@ For more details on the integration with Core ML and a sample app to get
 you started, please look at the the article on
 [Recognizing Objects in Live Capture](https://developer.apple.com/documentation/vision/recognizing_objects_in_live_capture).
 
+**Note:** The bounding box object `VNRecognizedObjectObservation.boundingBox` has a different definition from the one used for Turi Create. First, the location is defined by the lower-left corner of the bounding box instead of the center. Secondly, the coordinate space has origin located in the lower-left corner of image. Third, the location, width, and height for the bounding box are all normalized between [0,1] by the dimensions of the images.
+
 **Note:** Only models that were exported with *non-maximum suppression* (the default
 behavior in Turi Create 5.0+) will work with this example app. Older models
 or models that specify `include_non_maximum_suppression=False` will not give