Add code to States to not interpolate if an exact solution exists (#374)

* Update format of range conversion coefficients isd output to include a separate list for times. Also update driver, test data, and remove unneeded semicolons

* Fix documentaion error

* fix other documentation error

* Add code to states to not interpolate if there is already an exact value for a time (solves divide by 0 error in interpolation code.)

* Updated to be more efficient

* lower_bound can also return the last elt. don't do that

* Added test for when no interpolation is needed for getState

src/States.cpp

@@ -111,6 +111,16 @@ namespace ale {
 
 
   State States::getState(double time, PositionInterpolation interp) const {
+
+
+    // If time is in times, don't need to interpolate!
+    auto candidate_time = std::lower_bound(m_ephemTimes.begin(), m_ephemTimes.end(), time);
+
+    if ( (candidate_time != m_ephemTimes.end()) && (*candidate_time == time) ) {
+      int index = std::distance(m_ephemTimes.begin(), candidate_time);
+      return m_states[index];
+    }
+  
     if (m_ephemTimes.size() > 1) {
       int lowerBound = interpolationIndex(m_ephemTimes, time); 
       // try to copy the surrounding 8 points as that's the most possibly needed
@@ -132,7 +142,6 @@ namespace ale {
       }
 
       Vec3d position, velocity;
-
       if ( interp == LINEAR || (interp == SPLINE && !hasVelocity())) {
         position = {interpolate(xs,  interpTimes, time, interp, 0),
                     interpolate(ys,  interpTimes, time, interp, 0),
@@ -145,7 +154,6 @@ namespace ale {
       else if (interp == SPLINE && hasVelocity()){
         // Do hermite spline if velocities are available
         double baseTime = (interpTimes.front() + interpTimes.back()) / 2;
-
         std::vector<double> scaledEphemTimes;
         for(unsigned int i = 0; i < interpTimes.size(); i++) {
           scaledEphemTimes.push_back(interpTimes[i] - baseTime);
@@ -169,7 +177,7 @@ namespace ale {
       return State(position, velocity);
     }
     else { // Here we have: only 1 time and 1 state, so just return the only state.
-      return State(m_states[0]);
+      return m_states[0];
     }
   }
 

tests/ctests/StatesTests.cpp

@@ -347,6 +347,31 @@ TEST(StatesTest, OneStateWithVelocity) {
   EXPECT_NEAR(result.velocity.z, -1.0, 1e-6);
 }
 
+TEST(StatesTest, NoInterpNeeded) {
+  std::vector<double> ephemTimes = {0.0, 1.0, 2.0};
+
+  std::vector<Vec3d> positions = {
+    Vec3d(5.0, 3.0, 0.0),
+    Vec3d(6.5, 4.0, 1.0),
+    Vec3d(15.0, 4.0, 5.0)};
+
+  std::vector<Vec3d> velocities = {
+    Vec3d(5.0, 3.0, 0.0),
+    Vec3d(7.0, 6.0, 1.0),
+    Vec3d(15.0, 4.0, 5.0)};
+
+
+  States testState(ephemTimes, positions, velocities);
+  State result = testState.getState(1.0);
+  EXPECT_NEAR(result.position.x, 6.5, 1e-5);
+  EXPECT_NEAR(result.position.y, 4.0, 1e-4);
+  EXPECT_NEAR(result.position.z, 1.0, 1e-5);
+  EXPECT_NEAR(result.velocity.x, 7.0, 1e-6);
+  EXPECT_NEAR(result.velocity.y, 6.0, 1e-6);
+  EXPECT_NEAR(result.velocity.z, 1.0, 1e-6);
+}
+
+
 // This test checks to see if the minimized cache looks identical to ISIS's minimized cache for
 // a Dawn IR image VIR_IR_1A_1_362681634_1 (located in dawnvir2isis's IR app test.)
 // Values were obtained by adding strategic couts to SpicePosition.cpp, running spiceinit, and