More error checks to avoid div by zero.
Change-Id: I18e5b72d02bf5420c14334d3a03f18fa40572d31
diff --git a/services/sensorservice/Fusion.cpp b/services/sensorservice/Fusion.cpp
index ff4786b..e6ca2cc 100644
--- a/services/sensorservice/Fusion.cpp
+++ b/services/sensorservice/Fusion.cpp
@@ -47,9 +47,41 @@
static const float accSTDEV = 0.05f; // m/s^2 (measured 0.08 / CDD 0.05)
static const float magSTDEV = 0.5f; // uT (measured 0.7 / CDD 0.5)
-static const float FREE_FALL_THRESHOLD = 0.981f;
static const float SYMMETRY_TOLERANCE = 1e-10f;
+/*
+ * Accelerometer updates will not be performed near free fall to avoid ill-conditioning and
+ * div by zeros.
+ * Threshhold: 10% of g, in m/s^2
+ */
+static const float FREE_FALL_THRESHOLD = 0.981f;
+static const float FREE_FALL_THRESHOLD_SQ = FREE_FALL_THRESHOLD*FREE_FALL_THRESHOLD;
+
+/*
+ * The geomagnetic-field should be between 30uT and 60uT.
+ * Fields strengths greater than this likely indicate a local magnetic disturbance which
+ * we do not want to update into the fused frame.
+ */
+static const float MAX_VALID_MAGNETIC_FIELD = 100; // uT
+static const float MAX_VALID_MAGNETIC_FIELD_SQ = MAX_VALID_MAGNETIC_FIELD*MAX_VALID_MAGNETIC_FIELD;
+
+/*
+ * Values of the field smaller than this should be ignored in fusion to avoid ill-conditioning.
+ * This state can happen with anomalous local magnetic disturbances canceling the Earth field.
+ */
+static const float MIN_VALID_MAGNETIC_FIELD = 10; // uT
+static const float MIN_VALID_MAGNETIC_FIELD_SQ = MIN_VALID_MAGNETIC_FIELD*MIN_VALID_MAGNETIC_FIELD;
+
+/*
+ * If the cross product of two vectors has magnitude squared less than this, we reject it as
+ * invalid due to alignment of the vectors.
+ * This threshold is used to check for the case where the magnetic field sample is parallel to
+ * the gravity field, which can happen in certain places due to magnetic field disturbances.
+ */
+static const float MIN_VALID_CROSS_PRODUCT_MAG = 1.0e-3;
+static const float MIN_VALID_CROSS_PRODUCT_MAG_SQ =
+ MIN_VALID_CROSS_PRODUCT_MAG*MIN_VALID_CROSS_PRODUCT_MAG;
+
// -----------------------------------------------------------------------
template <typename TYPE, size_t C, size_t R>
@@ -240,8 +272,10 @@
status_t Fusion::handleAcc(const vec3_t& a) {
// ignore acceleration data if we're close to free-fall
- if (length(a) < FREE_FALL_THRESHOLD)
+ if (length_squared(a) < FREE_FALL_THRESHOLD_SQ) {
+ LOGW("handleAcc: near free fall, not updating!");
return BAD_VALUE;
+ }
if (!checkInitComplete(ACC, a))
return BAD_VALUE;
@@ -253,15 +287,32 @@
status_t Fusion::handleMag(const vec3_t& m) {
// the geomagnetic-field should be between 30uT and 60uT
- // reject obviously wrong magnetic-fields
- if (length(m) > 100)
+ // reject if too large to avoid spurious magnetic sources
+ const float magFieldSq = length_squared(m);
+ if (magFieldSq > MAX_VALID_MAGNETIC_FIELD_SQ) {
+ LOGW("handleMag: magnetic field too large, not updating!");
return BAD_VALUE;
+ } else if (magFieldSq < MIN_VALID_MAGNETIC_FIELD_SQ) {
+ // Also reject if too small since we will get ill-defined (zero mag) cross-products below
+ LOGW("handleMag: magnetic field too small, not updating!");
+ return BAD_VALUE;
+ }
if (!checkInitComplete(MAG, m))
return BAD_VALUE;
+ // Orthogonalize the magnetic field to the gravity field, mapping it into tangent to Earth.
const vec3_t up( getRotationMatrix() * Ba );
const vec3_t east( cross_product(m, up) );
+
+ // If the m and up vectors align, the cross product magnitude will approach 0.
+ // Reject this case as well to avoid div by zero problems and ill-conditioning below.
+ if (length_squared(east) < MIN_VALID_CROSS_PRODUCT_MAG_SQ) {
+ LOGW("handleMag: magnetic field too aligned with up vector, not updating!");
+ return BAD_VALUE;
+ }
+
+ // If we have created an orthogonal magnetic field successfully, then pass it in as the update.
vec3_t north( cross_product(up, east) );
const float l = 1 / length(north);