fix: velocity is now defined in terms of displacement instead of position_vector

example/kalman_filter/kalman_filter-example_2.cpp

@@ -61,7 +61,7 @@ void print(auto iteration, QuantityPoint auto measured, const kalman::SystemStat
 int main()
 {
   using namespace mp_units::si::unit_symbols;
-  using qp = quantity_point<isq::position_vector[m]>;
+  using qp = quantity_point<isq::displacement[m]>;
   using state = kalman::system_state<qp, quantity_point<isq::velocity[m / s]>>;
 
   const quantity interval = isq::duration(5 * s);

example/kalman_filter/kalman_filter-example_3.cpp

@@ -61,7 +61,7 @@ void print(auto iteration, QuantityPoint auto measured, const kalman::SystemStat
 int main()
 {
   using namespace mp_units::si::unit_symbols;
-  using qp = quantity_point<isq::position_vector[m]>;
+  using qp = quantity_point<isq::displacement[m]>;
   using state = kalman::system_state<qp, quantity_point<isq::velocity[m / s]>>;
 
   const quantity interval = isq::duration(5 * s);

example/kalman_filter/kalman_filter-example_4.cpp

@@ -62,7 +62,7 @@ void print(auto iteration, QuantityPoint auto measured, const kalman::SystemStat
 int main()
 {
   using namespace mp_units::si::unit_symbols;
-  using qp = quantity_point<isq::position_vector[m]>;
+  using qp = quantity_point<isq::displacement[m]>;
   using state =
     kalman::system_state<qp, quantity_point<isq::velocity[m / s]>, quantity_point<isq::acceleration[m / s2]>>;