Plane: QRTL: add interactive return path

plane/source/docs/qrtl-mode.rst

@@ -72,7 +72,8 @@ Return Altitude
 ===============
 
 If in a VTOL motors are active when QRTL is entered the vehicle will first climb vertically before returning home. The altitude to which the vehicle climbs depends on the distance from home as shown below.
-Altitude will be above terrain if terrain following is enabled, if not altitude will be above home.
+Altitude will be above terrain if terrain following is enabled, if not altitude will be above home. If the vehicle is within one and a half times :ref:`RTL_RADIUS<RTL_RADIUS>` or :ref:`WP_LOITER_RAD<WP_LOITER_RAD>`
+the vehicle we return in VTOL flight without transitioning into forward flight.
 
 .. raw:: html
 
@@ -95,10 +96,12 @@ Altitude will be above terrain if terrain following is enabled, if not altitude
    <input id="Q_LAND_FINAL" name="Q_LAND_FINAL" type="number" step="0.5" value="6" min="0" onchange="update()"/>
    </p>
 
-   <script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.4/Chart.js"></script>
+   <script src="https://cdn.jsdelivr.net/npm/chart.js"></script>
 
    <script>
    var chart
+   var vehicle_dist = 80
+   var vehicle_alt = 7
    function update() {
       var Q_RTL_ALT = parseFloat(document.getElementById("Q_RTL_ALT").value)
       var Q_RTL_ALT_MIN = parseFloat(document.getElementById("Q_RTL_ALT_MIN").value)
@@ -133,6 +136,20 @@ Altitude will be above terrain if terrain following is enabled, if not altitude
       var land_final = [{x:-5,             y:Q_LAND_FINAL},
                         {x:max_disp_rad+5, y:Q_LAND_FINAL}]
 
+      var threshold_alt = Math.max(Q_RTL_ALT * (vehicle_dist / Math.max(radius, vehicle_dist)), Q_RTL_ALT_MIN)
+
+      var return_path = []
+
+      return_path.push({x:vehicle_dist, y:vehicle_alt})
+      if (vehicle_alt < threshold_alt) {
+         return_path.push({x:vehicle_dist, y:threshold_alt})
+         return_path.push({x:0, y:threshold_alt})
+      } else {
+         return_path.push({x:vehicle_dist, y:vehicle_alt})
+         return_path.push({x:0, y:vehicle_alt})
+      }
+      return_path.push({x:0, y:0})
+
       if (chart == null) {
          chart = new Chart("QRTL_Altitude", {
             type : "scatter",
@@ -155,31 +172,46 @@ Altitude will be above terrain if terrain following is enabled, if not altitude
                         fill: false,
                         showLine: true,
                         lineTension: 0,
+                     },
+                     {
+                        label: 'Return Path',
+                        borderColor: "rgba(0,0,0,1)",
+                        pointBackgroundColor: "rgba(0,0,0,1)",
+                        data: return_path,
+                        fill: false,
+                        showLine: true,
+                        lineTension: 0,
                      }
                   ]
             },
             options: {
                   scales: {
-                     yAxes: [
-                        {
-                              scaleLabel: { display: true, labelString: "Altitude (m)" },
-                              ticks: {min:0.0, max:max_disp_alt}
-                        },
-                     ],
-                     xAxes: [
-                        {
-                              scaleLabel: { display: true, labelString: "Distance from home (m)" },
-                              ticks: { min:0.0, max:max_disp_rad}
-                        }
-                     ],
-                  }
+                     y: {
+                        scaleLabel: { display: true, labelString: "Altitude (m)" },
+                        min: 0.0,
+                        max: max_disp_alt
+                     },
+                     x: {
+                        scaleLabel: { display: true, labelString: "Distance from home (m)" },
+                        min: 0.0,
+                        max: max_disp_rad
+                     }
+                  },
+                  onClick: (e) => {
+                     var canvasPosition = Chart.helpers.getRelativePosition(e, chart)
+                     const {scales: {x, y}} = chart
+                     vehicle_dist = x.getValueForPixel(canvasPosition.x)
+                     vehicle_alt = y.getValueForPixel(canvasPosition.y)
+                     update()
+               }
             }
          });
       } else {
          chart.data.datasets[0].data = alt
          chart.data.datasets[1].data = land_final
-         chart.options.scales.xAxes[0].ticks.max = max_disp_rad
-         chart.options.scales.yAxes[0].ticks.max = max_disp_alt
+         chart.data.datasets[2].data = return_path
+         chart.options.scales.x.max = max_disp_rad
+         chart.options.scales.y.max = max_disp_alt
          chart.update()
       }
    }