Minimal example: synchronous mode#
Goals
Understand the synchronous mode.
Know the methods:
set_synchronous().trigger_next_simulation_step().wait_for_simulation_step_to_end().
We learned previously the asynchronous mode, the default operation mode. In this section we are going to see the
synchronous mode (now called stepped mode). In this mode, the simulation will take into account the progress of your script.
To enable it, you need to use set_synchronous(true).
Once enabled, the simulation will wait for a trigger to start computing the next simulation step. Such a trigger is sent by the
method trigger_next_simulation_step(). To keep the synchrony, we need to ensure that the simulation step is finished before sending the next trigger.
This can be done by using the method wait_for_simulation_step_to_end().
Recommendation
Check Legacy remote API modus operandi to learn more about the synchronous mode.
Templates:#
The templates show how to establish communication with a CoppeliaSim scene in synchronous mode using the default port. It’s assumed that both the script and
the scene are running in the same computer (default IP).
1clear all;
2close all;
3clc;
4
5
6include_namespace_dq;
7vi = DQ_VrepInterface();
8
9try
10 vi.connect('127.0.0.1', 19997);
11 vi.set_synchronous(true);
12 vi.start_simulation();
13 pause(0.1);
14 %-----------Your code here---------------------
15 vi.trigger_next_simulation_step();
16 vi.wait_for_simulation_step_to_end();
17 %----------------------------------------------
18 vi.stop_simulation();
19 vi.disconnect();
20catch ME
21 vi.stop_simulation();
22 vi.disconnect();
23 rethrow(ME)
24end
1#!/bin/python3
2from dqrobotics.interfaces.vrep import DQ_VrepInterface
3import time
4
5
6def main() -> None:
7 vi = DQ_VrepInterface()
8 try:
9 if not vi.connect("127.0.0.1", 19997, 100, 10):
10 raise RuntimeError("Unable to connect to CoppeliaSim.")
11
12 vi.set_synchronous(True)
13 vi.start_simulation()
14 time.sleep(0.1)
15 # --------------Your code here----------------------------
16 vi.trigger_next_simulation_step()
17 vi.wait_for_simulation_step_to_end()
18 # ---------------------------------------------------------
19
20 except (Exception, KeyboardInterrupt) as e:
21 print(e)
22 pass
23
24 finally:
25 vi.stop_simulation()
26 vi.disconnect()
27
28
29if __name__ == "__main__":
30 main()
1#include <iostream>
2#include <dqrobotics/interfaces/vrep/DQ_VrepInterface.h>
3#include <thread>
4
5int main()
6{
7 auto vi = DQ_VrepInterface();
8 try {
9 if (!vi.connect("127.0.0.1", 19997,100,10))
10 throw std::runtime_error("Unable to connect to CoppeliaSim.");
11 vi.set_synchronous(true);
12 vi.start_simulation();
13 std::this_thread::sleep_for(std::chrono::milliseconds(100));
14 //------------------Your code here--------------------------
15 vi.trigger_next_simulation_step();
16 vi.wait_for_simulation_step_to_end();
17 //---------------------------------------------------------
18 vi.stop_simulation();
19 vi.disconnect();
20
21 } catch (std::exception& e) {
22 std::cout<<e.what()<<std::endl;
23 vi.stop_simulation();
24 vi.disconnect();
25 }
26 return 0;
27}
See also
CMake examples for Ubuntu, Windows and MacOS dqrobotics/cpp-examples
1# Example CMAKE project for Ubuntu
2make_minimum_required(VERSION 3.5)
3
4project(template_synchronous)
5
6set(CMAKE_CXX_STANDARD 11)
7
8FIND_PACKAGE(Threads REQUIRED)
9FIND_PACKAGE(Eigen3 REQUIRED)
10INCLUDE_DIRECTORIES(${EIGEN3_INCLUDE_DIR})
11ADD_COMPILE_OPTIONS(-Werror=return-type
12 -Wall -Wextra -Wmissing-declarations
13 -Wredundant-decls -Woverloaded-virtual)
14
15add_executable(${PROJECT_NAME}
16 ${PROJECT_NAME}.cpp)
17
18target_link_libraries(${PROJECT_NAME}
19 dqrobotics
20 dqrobotics-interface-vrep
21 Threads::Threads)
Free fall experiment#
It’s time to test the synchronous mode! To do so, we are going to compare the height of the red ball (/Sphere)
that is in free fall with the expected height after 0.25 s in the simulation time. The dynamics of the red ball is
handled by the engine and its behavior is affected by the simulation time step and the gravity.
In the DQ_Robotics_lab.ttt scene (see One scene to rule them all), the engine is Newton, the simulation time step is 50ms and the gravity
is -9,81. You can modify those parameters, but you’ll need to update the examples as well.
Note
As reported in dqrobotics/python#51 the synchronous mode is working properly on Ubuntu (Matlab, Python and C++) and on Windows (Matlab). Other combinations of OS and languages could not ensure the synchrony.
1clear all;
2close all;
3clc;
4
5
6
7include_namespace_dq;
8vi = DQ_VrepInterface();
9
10
11try
12
13 vi.connect('127.0.0.1', 19997);
14 vi.set_synchronous(true);
15 vi.start_simulation();
16 pause(0.1);
17 p0 = vec3(translation(vi.get_object_pose('/Sphere')));
18 y0 = p0(3);
19 time_simulation_step = 0.05;
20 disp('---------------------------------')
21 disp(['Initial height: ',num2str(y0)])
22 disp('---------------------------------')
23
24 for i=0:5
25 t = i*time_simulation_step;
26 p = vec3(translation(vi.get_object_pose('/Sphere')));
27 y_sim = p(3);
28 y_est = y0 - 0.5*9.81*t^2;
29 vi.trigger_next_simulation_step();
30 vi.wait_for_simulation_step_to_end();
31 end
32 disp(['Elapsed time: ',num2str(t)])
33 disp(['Estimated height: ',num2str(y_est),' Measured height: ', num2str(y_sim)])
34 vi.stop_simulation();
35 vi.disconnect();
36
37catch ME
38
39 vi.stop_simulation();
40 vi.disconnect();
41 rethrow(ME)
42
43end
1#!/bin/python3
2from dqrobotics.interfaces.vrep import DQ_VrepInterface
3import time
4
5
6
7def main() -> None:
8 vi = DQ_VrepInterface()
9 try:
10 if not vi.connect("127.0.0.1", 19997, 100, 10):
11 raise RuntimeError("Unable to connect to CoppeliaSim.")
12
13 vi.set_synchronous(True)
14 vi.start_simulation()
15 time.sleep(0.1)
16 time_simulation_step = 0.05
17 y_0 = vi.get_object_pose("/Sphere").translation().vec3()[2]
18 print("---------------------------")
19 print("Initial height: ", y_0)
20 print("---------------------------")
21 for i in range(0, 6):
22 t = i * time_simulation_step
23 y_sim = vi.get_object_pose("/Sphere").translation().vec3()[2]
24 y_est = y_0 - 0.5 * 9.81 * pow(t, 2)
25 vi.trigger_next_simulation_step()
26 vi.wait_for_simulation_step_to_end()
27 print("Elapsed time: ", t)
28 print("Estimated height: ", y_est, "Measured height: ", y_sim)
29
30 except (Exception, KeyboardInterrupt) as e:
31 print(e)
32 pass
33
34 finally:
35 vi.stop_simulation()
36 vi.disconnect()
37
38
39if __name__ == "__main__":
40 main()
41
42
43
1#include <iostream>
2#include <dqrobotics/interfaces/vrep/DQ_VrepInterface.h>
3#include <thread>
4
5int main()
6{
7 auto vi = DQ_VrepInterface();
8 try {
9 if (!vi.connect("127.0.0.1", 19997,100,10))
10 throw std::runtime_error("Unable to connect to CoppeliaSim.");
11 vi.set_synchronous(true);
12 vi.start_simulation();
13 std::this_thread::sleep_for(std::chrono::milliseconds(100));
14 //---------------Your code here----------------------------
15
16 double time_simulation_step = 0.05;
17 double y_0 = vi.get_object_pose("/Sphere").translation().vec3()[2];
18 double y_sim;
19 double y_est;
20 double t;
21 std::cout<<"-----------------"<<std::endl;
22 std::cout<<"Initial height: "<<y_0<<std::endl;
23 std::cout<<"-----------------"<<std::endl;
24
25 for (int i=0; i<=5; i++)
26 {
27 t = i*time_simulation_step;
28 y_sim = vi.get_object_pose("/Sphere").translation().vec3()[2];
29 y_est = y_0 - 0.5 * 9.81 * std::pow(t, 2);
30 vi.trigger_next_simulation_step();
31 vi.wait_for_simulation_step_to_end();
32 }
33 std::cout<<"Elapsed time: "<<t<<std::endl;
34 std::cout<<"Estimated height: "<<y_est<<", Measured height: "<<y_sim<<std::endl;
35 vi.stop_simulation();
36 vi.disconnect();
37 } catch (std::exception& e) {
38 std::cout<<e.what()<<std::endl;
39 vi.stop_simulation();
40 vi.disconnect();
41 }
42 return 0;
43}
You will have the following output:
See also
Synchronous test dqrobotics/python-examples