diff --git a/schemas/typescript/CircleAnnotation.ts b/schemas/typescript/CircleAnnotation.ts
index 128c996..481b5e9 100644
--- a/schemas/typescript/CircleAnnotation.ts
+++ b/schemas/typescript/CircleAnnotation.ts
@@ -10,7 +10,10 @@ export type CircleAnnotation = {
   /** Timestamp of circle */
   timestamp: Time;
 
-  /** Center of the circle in 2D image coordinates (pixels) */
+  /** Center of the circle in 2D image coordinates (pixels) 
+   * The coordinate uses the top-left corner of the image as the origin.
+   * It is not centered on the pixel, but on the top-left corner of the pixel.
+  */
   position: Point2;
 
   /** Circle diameter in pixels */
diff --git a/schemas/typescript/PointsAnnotation.ts b/schemas/typescript/PointsAnnotation.ts
index 03fa1d7..75eb974 100644
--- a/schemas/typescript/PointsAnnotation.ts
+++ b/schemas/typescript/PointsAnnotation.ts
@@ -14,7 +14,10 @@ export type PointsAnnotation = {
   /** Type of points annotation to draw */
   type: PointsAnnotationType;
 
-  /** Points in 2D image coordinates (pixels) */
+  /** Points in 2D image coordinates (pixels) 
+   * The coordinate uses the top-left corner of the image as the origin.
+   * It is not centered on the pixel, but on the top-left corner of the pixel.
+  */
   points: Point2[];
 
   /** Outline color */
diff --git a/schemas/typescript/TextAnnotation.ts b/schemas/typescript/TextAnnotation.ts
index d5dc6bd..cb665e6 100644
--- a/schemas/typescript/TextAnnotation.ts
+++ b/schemas/typescript/TextAnnotation.ts
@@ -10,7 +10,10 @@ export type TextAnnotation = {
   /** Timestamp of annotation */
   timestamp: Time;
 
-  /** Bottom-left origin of the text label in 2D image coordinates (pixels) */
+  /** Bottom-left origin of the text label in 2D image coordinates (pixels)
+   * The coordinate uses the top-left corner of the image as the origin.
+   * It is not centered on the pixel, but on the top-left corner of the pixel.
+  */
   position: Point2;
 
   /** Text to display */