Changeset 11134 in ntrip

Timestamp:

Oct 28, 2026, 10:05:43 AM (3 hours ago)

Author:

stuerze

Message:

IIF shadow behaviour considerred in GPS attitude model

Location:

trunk/BNC

Files:

• CHANGELOG.md (modified) (1 diff)
• src/bncantex.cpp (modified) (1 diff)
• src/bncantex.h (modified) (2 diffs)
• src/bnchelp.html (modified) (2 diffs)

trunk/BNC/CHANGELOG.md

@@ -41 +41 @@
 - FIXED: Combination: the satellite offset of an AC was not reset after an outlier
 - FIXED: Combination: text of the combination logfile was lost
+- CHANGED: GPS attitude model ('Computed'): Block IIF satellites in the Earth's shadow yaw at a constant rate from their yaw at shadow entry to the nominal yaw at shadow exit (before: nominal yaw-steering with maximum rate, up to 37 deg off during eclipses, i.e. 25 cm in the APC/CoM conversion with the IIF x offset of 0.39 m)
 - FIXED: GPS attitude model ('Computed'): at the end of a noon/midnight turn the yaw jumped to the nominal yaw (e.g. by 95 deg); the satellite now keeps yawing at its maximum rate until it has caught up with the nominal yaw
 - FIXED: GLONASS attitude model ('Computed'): the yaw was frozen while the nominal yaw rate exceeded the maximum rate and then jumped to the nominal yaw; now following Dilssner et al. (2011), the satellite yaws at the maximum rate (0.25 deg/s) during noon turns until it has caught up, and in the Earth's shadow until it reaches the nominal yaw at shadow exit

trunk/BNC/src/bncantex.cpp

@@ -632 +632 @@
       prn.toLatin1().data(), Mjd, beta*180.0/M_PI, mu*180.0/M_PI,
       st.yaw*180.0/M_PI, psiNom*180.0/M_PI, callGap*1440.0);
-    st.valid  = false;
-    st.inTurn = false;
+    st.valid    = false;
+    st.inTurn   = false;
+    st.inShadow = false;
+  }
+
+  // Block IIF in the Earth's shadow (cylinder, around midnight for |mu| <
+  // muShadow): the satellite yaws at a constant rate from its yaw at shadow
+  // entry to the nominal yaw at shadow exit (Kouba 2009, Dilssner 2010)
+  // -------------------------------------------------------------------------
+  if (blockType == "IIF") {
+    const double RE = 6378137.0;
+    double cosMuShadow = sqrt(std::max(0.0, 1.0 - RE * RE / (r * r))) / cos(beta);
+    bool   inShadow    = (cosMuShadow < 1.0 && cos(mu) > cosMuShadow);
+    if (inShadow) {
+      double muExit = acos(cosMuShadow);
+      if (!st.inShadow) {
+        double psiExit = atan2(-tanBeta, sin(muExit));      // nominal yaw at shadow exit
+        double tRem    = (muExit - mu) / nRate;              // remaining time in the shadow [s]
+        st.inShadow   = true;
+        st.shadowYaw0 = st.valid ? st.yaw : psiNom;
+        st.shadowRate = (tRem > 0.0) ? remainder(psiExit - st.shadowYaw0, 2.0 * M_PI) / tRem : 0.0;
+        st.shadowMjd0 = Mjd;
+        _gpsYawLog += QString().asprintf(
+          "%s gpsYaw SHADOW-ENTER Mjd=%.6f beta=%6.3f mu=%7.2f yaw=%7.2f exit=%7.2f rate=%6.3f\n",
+          prn.toLatin1().data(), Mjd, beta*180.0/M_PI, mu*180.0/M_PI, st.shadowYaw0*180.0/M_PI,
+          psiExit*180.0/M_PI, st.shadowRate*180.0/M_PI);
+      }
+      double psiEff = st.shadowYaw0 + st.shadowRate * (Mjd - st.shadowMjd0) * 86400.0;
+      while (psiEff >  M_PI) psiEff -= 2.0 * M_PI;
+      while (psiEff < -M_PI) psiEff += 2.0 * M_PI;
+      st.yaw         = psiEff;
+      st.lastCallMjd = Mjd;
+      st.valid       = true;
+      st.inTurn      = false;
+      return psiEff;
+    }
+    else if (st.inShadow) {
+      // shadow exit: a remaining difference to the nominal yaw is caught up
+      // at the maximum rate (catch-up branch below)
+      st.inShadow = false;
+      st.inTurn   = true;
+      st.turnSign = (remainder(psiNom - st.yaw, 2.0 * M_PI) >= 0.0) ? 1.0 : -1.0;
+      _gpsYawLog += QString().asprintf(
+        "%s gpsYaw SHADOW-EXIT  Mjd=%.6f beta=%6.3f mu=%7.2f yaw=%7.2f nominal=%7.2f\n",
+        prn.toLatin1().data(), Mjd, beta*180.0/M_PI, mu*180.0/M_PI, st.yaw*180.0/M_PI, psiNom*180.0/M_PI);
+    }
   }
 

trunk/BNC/src/bncantex.h

@@ -126 +126 @@
       inTurn      = false;
       turnSign    = 1.0;
+      inShadow    = false;
+      shadowYaw0  = 0.0;
+      shadowRate  = 0.0;
+      shadowMjd0  = 0.0;
     }
     double yaw;
@@ -132 +136 @@
     bool   inTurn;    // true while in a constrained noon/midnight turn
     double turnSign;  // direction of the turn (sign of the nominal yaw rate at its start)
+    bool   inShadow;    // Block IIF in the Earth's shadow
+    double shadowYaw0;  // yaw at shadow entry [rad]
+    double shadowRate;  // constant yaw rate in the shadow [rad/s]
+    double shadowMjd0;  // shadow entry
   };
 

trunk/BNC/src/bnchelp.html

@@ -5262 +5262 @@
   <pre>
   G attitude check G14 09:42:30-10:25:30: yaw difference to the model 362 deg, clock change vs. consensus 8.2 cm, predicted 10.7 cm (max 10.7 cm), slope 0.77, clock RMS 6.1 -> 2.0 cm: SSR yaw consistent with the clocks
-  G attitude check G25 07:53:00-08:51:30: yaw difference to the model 39 deg, clock change vs. consensus -9.8 cm, predicted -0.0 cm (max 1.2 cm), slope 1.84, clock RMS 5.9 -> 5.8 cm: clock change not explained by the yaw difference (the other ACs model this turn differently?)
 </pre>
   <p>
@@ -8379 +8378 @@
   <ul>
     <li><b>Computed</b> (default): BNC applies its own kinematic attitude model:
-      GPS noon/midnight turn manoeuvres (Kouba 2009/2015, Bar-Sever 1996),
+      GPS noon/midnight turn manoeuvres (Kouba 2009/2015, Bar-Sever 1996), with Block IIF satellites in the Earth's
+      shadow yawing at a constant rate from their yaw at shadow entry to the nominal yaw at shadow exit,
       GLONASS-M noon turns and midnight turns in the Earth's shadow (Dilssner et al. 2011), and
       Galileo / BDS orbit-normal mode switching (Kouba 2017, Dai et al. 2015, Steigenberger et al. 2018).</li>