Merge pull request #6 from nytm/fix/noise-filter

Add a low-pass noise filter.

Sources/NYT360CameraController.m

@@ -69,7 +69,7 @@ - (void)updateCameraAngle {
     CMRotationRate rotationRate = self.motionManager.deviceMotion.rotationRate;
     UIInterfaceOrientation orientation = [UIApplication sharedApplication].statusBarOrientation;
     NYT360EulerAngleCalculationResult result;
-    result = NYT360DeviceMotionCalculation(self.currentPosition, rotationRate, orientation, self.allowedPanningAxes);
+    result = NYT360DeviceMotionCalculation(self.currentPosition, rotationRate, orientation, self.allowedPanningAxes, NYT360EulerAngleCalculationNoiseThresholdDefault);
     self.currentPosition = result.position;
     self.camera.eulerAngles = result.eulerAngles;
 }

Sources/NYT360EulerAngleCalculations.h

@@ -10,6 +10,8 @@
 @import SceneKit;
 @import CoreMotion;
 
+extern CGFloat const NYT360EulerAngleCalculationNoiseThresholdDefault;
+
 #import "NYT360DataTypes.h"
 
 #pragma mark - Data Types
@@ -24,6 +26,6 @@ typedef struct NYT360EulerAngleCalculationResult NYT360EulerAngleCalculationResu
 
 NYT360EulerAngleCalculationResult NYT360UpdatedPositionAndAnglesForAllowedAxes(CGPoint position, NYT360PanningAxis allowedPanningAxes);
 
-NYT360EulerAngleCalculationResult NYT360DeviceMotionCalculation(CGPoint position, CMRotationRate rotationRate, UIInterfaceOrientation orientation, NYT360PanningAxis allowedPanningAxes);
+NYT360EulerAngleCalculationResult NYT360DeviceMotionCalculation(CGPoint position, CMRotationRate rotationRate, UIInterfaceOrientation orientation, NYT360PanningAxis allowedPanningAxes, CGFloat noiseThreshold);
 
 NYT360EulerAngleCalculationResult NYT360PanGestureChangeCalculation(CGPoint position, CGPoint rotateDelta, CGSize viewSize, NYT360PanningAxis allowedPanningAxes);

Sources/NYT360EulerAngleCalculations.m

@@ -10,6 +10,7 @@
 
 #pragma mark - Constants
 
+CGFloat const NYT360EulerAngleCalculationNoiseThresholdDefault = 0.12;
 static CGFloat NYT360EulerAngleCalculationRotationRateDampingFactor = 0.02;
 
 #pragma mark - Inline Functions
@@ -45,7 +46,29 @@ NYT360EulerAngleCalculationResult NYT360UpdatedPositionAndAnglesForAllowedAxes(C
     return NYT360EulerAngleCalculationResultMake(position, eulerAngles);
 }
 
-NYT360EulerAngleCalculationResult NYT360DeviceMotionCalculation(CGPoint position, CMRotationRate rotationRate, UIInterfaceOrientation orientation, NYT360PanningAxis allowedPanningAxes) {
+NYT360EulerAngleCalculationResult NYT360DeviceMotionCalculation(CGPoint position, CMRotationRate rotationRate, UIInterfaceOrientation orientation, NYT360PanningAxis allowedPanningAxes, CGFloat noiseThreshold) {
+
+    // On some devices, the rotation rates exhibit a low-level drift on one or
+    // more rotation axes. The symptom expressions are not identical, but they
+    // appear to be related to low component quality (iPhone 5c versus higher
+    // end devices) and/or rough usage (drops, etc). In an ideal scenario, we
+    // could ask users to calibrate their gyroscopes and apply a corrective
+    // factor to all inputs. Barring that, the next best thing we can try is to
+    // add a low-pass filter which ignores input less than a given threshold.
+    // In my non-scientific testing with the only affected devices at my
+    // disposal, I found that a noise threshold between 0.10 and 0.15 filtered
+    // out the noise with a minimal loss in sensitivity. Less than 0.10 and the
+    // 360 camera position starts to drift.
+    // ~ Jared Sinclair, August 1, 2016.
+    // See also: https://forums.developer.apple.com/thread/12049
+
+    if (fabs(rotationRate.x) < noiseThreshold) {
+        rotationRate.x = 0;
+    }
+
+    if (fabs(rotationRate.y) < noiseThreshold) {
+        rotationRate.y = 0;
+    }
 
     CGFloat damping = NYT360EulerAngleCalculationRotationRateDampingFactor;
 

Three60_PlayerTests/NYT360EulerAngleCalculationsTests.m

@@ -38,7 +38,7 @@ - (void)testDeviceMotionFunctionShouldZeroOutDisallowedYAxis {
     rate.y = -1000;
     rate.z = 10;
     UIInterfaceOrientation orientation = UIInterfaceOrientationLandscapeLeft;
-    NYT360EulerAngleCalculationResult result = NYT360DeviceMotionCalculation(position, rate, orientation, NYT360PanningAxisHorizontal);
+    NYT360EulerAngleCalculationResult result = NYT360DeviceMotionCalculation(position, rate, orientation, NYT360PanningAxisHorizontal, NYT360EulerAngleCalculationNoiseThresholdDefault);
     XCTAssertNotEqual(result.position.x, 0);
     XCTAssertEqual(result.position.y, 0);
 }
@@ -50,11 +50,59 @@ - (void)testDeviceMotionFunctionShouldZeroOutDisallowedXAxis {
     rate.y = -1000;
     rate.z = 10;
     UIInterfaceOrientation orientation = UIInterfaceOrientationLandscapeLeft;
-    NYT360EulerAngleCalculationResult result = NYT360DeviceMotionCalculation(position, rate, orientation, NYT360PanningAxisVertical);
+    NYT360EulerAngleCalculationResult result = NYT360DeviceMotionCalculation(position, rate, orientation, NYT360PanningAxisVertical, NYT360EulerAngleCalculationNoiseThresholdDefault);
     XCTAssertEqual(result.position.x, 0);
     XCTAssertNotEqual(result.position.y, 0);
 }
 
+- (void)testDeviceMotionFunctionShouldFilterOutNegativeXRotationNoise {
+    CGPoint position = CGPointMake(100, 100);
+    CMRotationRate rate;
+    rate.x = NYT360EulerAngleCalculationNoiseThresholdDefault * -0.5;
+    rate.y = NYT360EulerAngleCalculationNoiseThresholdDefault * 2;
+    rate.z = 10;
+    UIInterfaceOrientation orientation = UIInterfaceOrientationLandscapeLeft;
+    NYT360EulerAngleCalculationResult result = NYT360DeviceMotionCalculation(position, rate, orientation, NYT360PanningAxisHorizontal, NYT360EulerAngleCalculationNoiseThresholdDefault);
+    XCTAssertEqual(result.position.x, position.x);
+    XCTAssertNotEqual(result.position.y, position.y);
+}
+
+- (void)testDeviceMotionFunctionShouldFilterOutPositiveXRotationNoise {
+    CGPoint position = CGPointMake(100, 100);
+    CMRotationRate rate;
+    rate.x = NYT360EulerAngleCalculationNoiseThresholdDefault * 0.5;
+    rate.y = NYT360EulerAngleCalculationNoiseThresholdDefault * 2;
+    rate.z = 10;
+    UIInterfaceOrientation orientation = UIInterfaceOrientationLandscapeLeft;
+    NYT360EulerAngleCalculationResult result = NYT360DeviceMotionCalculation(position, rate, orientation, NYT360PanningAxisHorizontal, NYT360EulerAngleCalculationNoiseThresholdDefault);
+    XCTAssertEqual(result.position.x, position.x);
+    XCTAssertNotEqual(result.position.y, position.y);
+}
+
+- (void)testDeviceMotionFunctionShouldFilterOutNegativeYRotationNoise {
+    CGPoint position = CGPointMake(100, 100);
+    CMRotationRate rate;
+    rate.x = NYT360EulerAngleCalculationNoiseThresholdDefault * 2;
+    rate.y = NYT360EulerAngleCalculationNoiseThresholdDefault * -0.5;
+    rate.z = 10;
+    UIInterfaceOrientation orientation = UIInterfaceOrientationLandscapeLeft;
+    NYT360EulerAngleCalculationResult result = NYT360DeviceMotionCalculation(position, rate, orientation, NYT360PanningAxisHorizontal, NYT360EulerAngleCalculationNoiseThresholdDefault);
+    XCTAssertNotEqual(result.position.x, 0);
+    XCTAssertEqual(result.position.y, 0);
+}
+
+- (void)testDeviceMotionFunctionShouldFilterOutPositiveYRotationNoise {
+    CGPoint position = CGPointMake(100, 100);
+    CMRotationRate rate;
+    rate.x = NYT360EulerAngleCalculationNoiseThresholdDefault * 2;
+    rate.y = NYT360EulerAngleCalculationNoiseThresholdDefault * 0.5;
+    rate.z = 10;
+    UIInterfaceOrientation orientation = UIInterfaceOrientationLandscapeLeft;
+    NYT360EulerAngleCalculationResult result = NYT360DeviceMotionCalculation(position, rate, orientation, NYT360PanningAxisHorizontal, NYT360EulerAngleCalculationNoiseThresholdDefault);
+    XCTAssertNotEqual(result.position.x, 0);
+    XCTAssertEqual(result.position.y, 0);
+}
+
 - (void)testPanGestureChangeFunctionShouldZeroOutDisallowedYAxis {
     CGPoint position = CGPointMake(100, 100);
     CGPoint delta = CGPointMake(1000, -1000);