to be added in cv.cpp

 #include <fcntl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
 #include <stdio.h>
 
 #define IMUPIPE "/tmp/fromimu"
 float msgpipe_g[3];
 int imufd;
 Point pcenter(320,240);
 float torad = CV_PI / 180.0;
 
 /*****************************************************************************/
 static void * drawAxes_threadImuProg(void *arg) {
   float msgpipe_l[3];
   int msgsize = sizeof(msgpipe_g);
   while(true) {
     if (msgsize==read(imufd,&msgpipe_l,msgsize)) {
       memcpy(&msgpipe_g, &msgpipe_l, msgsize); 
     } 
   }
 }
 
 static void drawAxes_init()
 {
   mkfifo(IMUPIPE, 0666); 
   imufd = open(IMUPIPE, O_RDWR);
 
   pthread_t threadImu;
   pthread_create(&threadImu, NULL, &drawAxes_threadImuProg, NULL);
 }
 
 struct quaternion_t
 {
   float w, x, y, z;
 };
 
 static void drawAxes(Mat3b *img) 
 {
   float msgpipe_l[3];
   memcpy(&msgpipe_l, &msgpipe_g, sizeof(msgpipe_g)); 
 
   float roll  =  torad*msgpipe_l[0];   // roll_phy(x)
   float pitch = -torad*msgpipe_l[1]; // pitch_theta(y)
   float yaw   = -torad*msgpipe_l[2];   // yaw_psi(z)
 
   float cy = cos(roll * 0.5);
   float sy = sin(roll * 0.5);
   float cp = cos(yaw * 0.5);
   float sp = sin(yaw * 0.5);
   float cr = cos(pitch * 0.5);
   float sr = sin(pitch * 0.5);
 
   quaternion_t q;          // quaternion from euler
   q.w = cr * cp * cy + sr * sp * sy;
   q.x = sr * cp * cy - cr * sp * sy;
   q.y = cr * sp * cy + sr * cp * sy;
   q.z = cr * cp * sy - sr * sp * cy;
 
   array<Point3i,4> pts = {Point3i{0,0,0},Point3i{100,0,0},Point3i{0,100,0},Point3i{0,0,100}};
   array<Point3f,4> out;
   for (int i=0;i<4;i++) {  // rotation matrix from quaternion
     out[i].x=(1-2*q.y*q.y-2*q.z*q.z)*pts[i].x+(2*q.x*q.y-2*q.z*q.w)*pts[i].y+(2*q.x*q.z+2*q.y*q.w)*pts[i].z;
     out[i].y=(2*q.x*q.y+2*q.z*q.w)*pts[i].x+(1-2*q.x*q.x-2*q.z*q.z)*pts[i].y+(2*q.y*q.z-2*q.x*q.w)*pts[i].z;
     out[i].z=(2*q.x*q.z-2*q.y*q.w)*pts[i].x+(2*q.y*q.z+2*q.x*q.w)*pts[i].y+(1-2*q.x*q.x-2*q.y*q.y)*pts[i].z;
   } 
 
   Point loc=pcenter;
   array<Point,4> imgPts;   // 3D to 2D projection
   for (int i=0;i<4;i++)
     imgPts[i]={(int)(loc.x-out[i].x+0.5*out[i].z),(int)(loc.y-out[i].y-0.5*out[i].z)}; 
 
   line(*img, imgPts[0], imgPts[3], Scalar(0,0,255), 3); // red
   line(*img, imgPts[0], imgPts[1], Scalar(0,255,0), 3); // green
   line(*img, imgPts[0], imgPts[2], Scalar(255,0,0), 3); // blue
   circle(*img, pcenter, 5, Scalar(0,0,0), -1);
 }

to be modified in muxer.c

 #define IMUPIPE "/tmp/fromimu"
 float msgpipe_g[3];
 int imufd;
 ...
       mkfifo(IMUPIPE, 0666); 
      imufd = open(IMUPIPE, O_RDWR | O_NONBLOCK);
 ...
             if (msgid == PPRZ_MSG_ID_ROTORCRAFT_FP) {
       	      memcpy(&(rfp_g.stamp),&tv,sizeof(struct timeval));
               rfp_g.phi  =ALT_UNIT_COEF_ATT*pprzlink_get_ROTORCRAFT_FP_phi(buf);
               rfp_g.theta=ALT_UNIT_COEF_ATT*pprzlink_get_ROTORCRAFT_FP_theta(buf);
               rfp_g.psi  =ALT_UNIT_COEF_ATT*pprzlink_get_ROTORCRAFT_FP_psi(buf);
   	       acid = buf[0];
               printf("%.4f %d ROTORCRAFT_FP %f %f %f\n",elapsed,acid,rfp_g.phi,rfp_g.theta,rfp_g.psi);  
 
               msgpipe_g[0]=rfp_g.phi; msgpipe_g[1]=rfp_g.theta; msgpipe_g[2] = rfp_g.psi;
               write(imufd, &msgpipe_g, sizeof(msgpipe_g));

to be modified in airpi.sh

 socat -u /dev/ttyAMA0,raw,echo=0,b115200 - | tee >(socat - udp-sendto:127.0.0.1:4245) >(socat - udp-sendto:127.0.0.1:4242) > /dev/null 2>&1 &
 socat -u udp-listen:4243,reuseaddr,fork /dev/ttyAMA0,raw,echo=0,b115200 &
 export LD_LIBRARY_PATH=/home/pi/muxer/lib
 /home/pi/muxer/exe/muxer 4244 4245 > /dev/null 2>&1 &