diff --git a/MAGFit/index.html b/MAGFit/index.html
index 4da50d67..bb1d86ab 100644
--- a/MAGFit/index.html
+++ b/MAGFit/index.html
@@ -91,10 +91,10 @@ <h1 style="text-align:center"><a href="" style="color: #000000; text-decoration:
         </td>
         <td style="width: 10px;"></td>
         <td>
-            <fieldset style="width:200px;height:80px" id="ATTITUDE">
+            <fieldset style="width:200px;min-height:80px" id="ATTITUDE">
                 <legend>Attitude source
                     <img id="TT" src="../images/question-circle.svg" style="width: 1em; vertical-align: bottom" 
-                    data-tippy-content='Select the attitude source that will be used for the MAGFit, this should best represent the true attitude of the vehicle, typically the default is fine, if you know there were EKF issues using DCM may give better results. The Calculate button must be clicked after any change of source.'
+                    data-tippy-content='Select the attitude source that will be used for the MAGFit, this should best represent the true attitude of the vehicle, typically the default is fine, if you know there were EKF issues using DCM may give better results. GSF yaw and GPS yaw use the EKF roll and pitch with yaw from the EKF&#39;s GSF yaw estimator or from a GPS that provides yaw, these do not use the compass so can be used if a bad compass has upset the EKF yaw. They are only available for part of the flight, selecting one limits the analysis time to that part. The Calculate button must be clicked after any change of source.'
                     data-tippy-maxWidth='750px'/>
                 </legend>
             </fieldset>
diff --git a/MAGFit/magfit.js b/MAGFit/magfit.js
index 7f312942..4ff9672e 100644
--- a/MAGFit/magfit.js
+++ b/MAGFit/magfit.js
@@ -1715,7 +1715,62 @@ function set_need_calc(b) {
     document.getElementById('SaveParams').disabled = b
 }
 
-function add_attitude_source(quaternion, name) {
+// Make a new attitude using the roll and pitch from quaternion and the yaw (deg) from another source.
+// Only the times where yaw is available are used, gaps of more than 1 second in the yaw are skipped.
+function replace_yaw(quaternion, yaw_time, yaw_deg) {
+    const yaw_len = yaw_time.length
+    if (yaw_len < 2) {
+        return
+    }
+
+    // Unwrap so yaw can be interpolated
+    let yaw = new Array(yaw_len)
+    yaw[0] = yaw_deg[0]
+    for (let i = 1; i < yaw_len; i++) {
+        let delta = yaw_deg[i] - yaw_deg[i-1]
+        delta -= 360 * Math.round(delta / 360)
+        yaw[i] = yaw[i-1] + delta
+    }
+
+    let ret = { time: [], q1: [], q2: [], q3: [], q4: [] }
+    let q = new Quaternion()
+    let yaw_index = 0
+    for (let i = 0; i < quaternion.time.length; i++) {
+        const time = quaternion.time[i]
+        if ((time < yaw_time[0]) || (time > yaw_time[yaw_len - 1])) {
+            continue
+        }
+        while ((yaw_index < yaw_len - 2) && (yaw_time[yaw_index + 1] < time)) {
+            yaw_index++
+        }
+        const dt = yaw_time[yaw_index + 1] - yaw_time[yaw_index]
+        if (dt > 1.0) {
+            continue
+        }
+        const ratio = (dt > 0) ? (time - yaw_time[yaw_index]) / dt : 0
+        const new_yaw = yaw[yaw_index] + (yaw[yaw_index + 1] - yaw[yaw_index]) * ratio
+
+        q.q1 = quaternion.q1[i]
+        q.q2 = quaternion.q2[i]
+        q.q3 = quaternion.q3[i]
+        q.q4 = quaternion.q4[i]
+        q.from_euler(q.get_euler_roll(), q.get_euler_pitch(), new_yaw * (Math.PI / 180))
+
+        ret.time.push(time)
+        ret.q1.push(q.q1)
+        ret.q2.push(q.q2)
+        ret.q3.push(q.q3)
+        ret.q4.push(q.q4)
+    }
+
+    if (ret.time.length < 2) {
+        return
+    }
+    return ret
+}
+
+// time_range is optional, if given the analysis time is limited to it when this source is selected
+function add_attitude_source(quaternion, name, time_range) {
 
     // Add check box for this attitude source
     let section = document.getElementById("ATTITUDE")
@@ -1730,6 +1785,15 @@ function add_attitude_source(quaternion, name) {
     radio.addEventListener('change', function() { 
         set_need_calc(true)
         source = null
+
+        if (time_range != null) {
+            // Limit analysis time to the period this source is valid for
+            let start = document.getElementById("TimeStart")
+            let end = document.getElementById("TimeEnd")
+            start.value = Math.min(Math.max(parseFloat(start.value), time_range[0]), time_range[1])
+            end.value = Math.max(Math.min(parseFloat(end.value), time_range[1]), time_range[0])
+            time_range_changed()
+        }
     })
 
     let label = document.createElement("label")
@@ -2064,6 +2128,53 @@ async function load(log_file) {
                 field.select.checked = true
             }
             body_frame_earth_field.push(field)
+
+            // EKF roll and pitch with yaw from the EKF's Gaussian sum filter (GSF) yaw estimator, this does not use the compass
+            if (("XKY0" in log.messageTypes) && ("instances" in log.messageTypes.XKY0) && (primary in log.messageTypes.XKY0.instances)) {
+                const time = TimeUS_to_seconds(log.get_instance("XKY0", primary, "TimeUS"))
+                const yaw = log.get_instance("XKY0", primary, "YC")
+                const yaw_sd = log.get_instance("XKY0", primary, "YCS")
+
+                // Use the same accuracy threshold as the EKF does for a yaw reset (GSF_YAW_ACCURACY_THRESHOLD_DEG)
+                // YCS is logged as sqrt(degrees(variance)) so convert the threshold to match
+                const threshold = Math.sqrt((15.0 * (Math.PI / 180))**2 * (180 / Math.PI))
+                let valid_time = []
+                let valid_yaw = []
+                for (let i = 0; i < time.length; i++) {
+                    if (yaw_sd[i] < threshold) {
+                        valid_time.push(time[i])
+                        valid_yaw.push(yaw[i])
+                    }
+                }
+
+                const GSF_quaternion = replace_yaw(quaternion, valid_time, valid_yaw)
+                if (GSF_quaternion != null) {
+                    const range = [GSF_quaternion.time[0], GSF_quaternion.time[GSF_quaternion.time.length - 1]]
+                    body_frame_earth_field.push(add_attitude_source(GSF_quaternion, "EKF 3 IMU " + (primary + 1) + " GSF yaw", range))
+                }
+            }
+
+            // EKF roll and pitch with yaw from GPS (for example moving baseline), yaw is logged as 0 when not available
+            if (("GPS" in log.messageTypes) && ("instances" in log.messageTypes.GPS)) {
+                for (const inst of Object.keys(log.messageTypes.GPS.instances)) {
+                    const time = TimeUS_to_seconds(log.get_instance("GPS", inst, "TimeUS"))
+                    const yaw = log.get_instance("GPS", inst, "Yaw")
+                    let valid_time = []
+                    let valid_yaw = []
+                    for (let i = 0; i < time.length; i++) {
+                        if (yaw[i] != 0) {
+                            valid_time.push(time[i])
+                            valid_yaw.push(yaw[i])
+                        }
+                    }
+
+                    const GPS_quaternion = replace_yaw(quaternion, valid_time, valid_yaw)
+                    if (GPS_quaternion != null) {
+                        const range = [GPS_quaternion.time[0], GPS_quaternion.time[GPS_quaternion.time.length - 1]]
+                        body_frame_earth_field.push(add_attitude_source(GPS_quaternion, "EKF 3 IMU " + (primary + 1) + " GPS " + (parseFloat(inst) + 1) + " yaw", range))
+                    }
+                }
+            }
         }
     }