Initial commit of model/Thrustcurve that uses linear interpolation

CMakeLists.txt

@@ -26,6 +26,7 @@ enable_testing()
 add_subdirectory(src/gui)
 add_subdirectory(src/sim)
 add_subdirectory(src/Utils)
+add_subdirectory(src/model)
 
 #find_package(wxWidgets REQUIRED gl core base)
 #include(${wxWidgets_USE_FILE})

src/model/CMakeLists.txt

@@ -0,0 +1,3 @@
+add_library(model
+   Thrustcurve.cpp)
+

src/model/Thrustcurve.cpp

@@ -0,0 +1,60 @@
+#include "Thrustcurve.h"
+
+#include <algorithm>
+
+Thrustcurve::Thrustcurve(std::vector<std::pair<double, double>>& tc)
+   : thrustCurve(tc),
+     maxTime(0.0)
+{
+   maxTime = std::max_element(thrustCurve.begin(),
+                              thrustCurve.end(),
+                              [](const auto& a, const auto& b)
+                              {
+                                 return a.first < a.second;
+                              })->first;
+}
+
+Thrustcurve::Thrustcurve()
+{
+   thrustCurve.emplace_back(0.0, 0.0);
+   maxTime = 0.0;
+}
+
+Thrustcurve::~Thrustcurve()
+{}
+
+double Thrustcurve::getThrust(double t)
+{
+   if(t < 0.0 || t > maxTime)
+   {
+      return 0.0;
+   }
+
+   // Find the right interval
+   auto i = thrustCurve.cbegin();
+   while(i->first <= t)
+   {
+      // If t is equal to a data point that we have, then just return
+      // the thrust we know. Otherwise it fell between  two points and we
+      // will interpolate
+      if(i->first == t)
+      {
+         return i->second;
+      }
+      else
+      {
+         i++;
+      }
+   }
+   // linearly interpolate the thrust and return
+   // tStart and tEnd are the start time and the end time
+   // of the current interval. thrustStart is the thrust at
+   // the start of the interval. 
+   double tStart = std::prev(i)->first;
+   double thrustStart = std::prev(i)->second;
+   double tEnd = i->first;
+   double slope = (i->second - std::prev(i)->second) / 
+                  (i->first - std::prev(i)->first);
+   return thrustStart + (t - tStart) * slope;
+
+}

src/model/Thrustcurve.h

@@ -0,0 +1,38 @@
+#ifndef MODEL_THRUSTCURVE_H
+#define MODEL_THRUSTCURVE_H
+
+#include <vector>
+#include <tuple>
+
+// No namespace. Maybe should be, but this is a model rocket program
+// so model is sort of implied? Or I'm just making excuses for being lazy
+
+class Thrustcurve
+{
+public:
+   /**
+    * Constructor takes a vector of pairs. The first item a timestamp,
+    * the second the thrust in newtons.
+   */
+   Thrustcurve(std::vector<std::pair<double, double>>& tc);
+   /**
+    * Default constructor. Will create an empty thrustcurve, always returning 0.0
+    * for all requested times.
+   */
+   Thrustcurve();
+   ~Thrustcurve();
+
+   /**
+    * Assuming that the thrust is one dimensional. Seems reasonable, but just
+    * documenting that for the record. For timesteps between known points the thrust
+    * is interpolated linearly
+    * @param t The time in seconds. For t > burntime or < 0, this will return 0.0
+    * @return Thrust in Newtons
+   */
+  double getThrust(double t);
+
+private:
+   std::vector<std::pair<double, double>> thrustCurve;
+   double maxTime;
+};
+#endif // MODEL_THRUSTCURVE_H