diff --git a/TC_NAV_Zjut_post/Src/post/ps_tcpos.c b/TC_NAV_Zjut_post/Src/post/ps_tcpos.c
index b604a35..f2ef800 100644
--- a/TC_NAV_Zjut_post/Src/post/ps_tcpos.c
+++ b/TC_NAV_Zjut_post/Src/post/ps_tcpos.c
@@ -474,7 +474,7 @@ static int tcfilter()
             outsolstat(&svr.rtk,&nav);
         }
         /* non-holonomic constraint */
-//        nhc(&svr.rtk.ins,&svr.rtk.opt.insopt,&imud);
+        nhc(&svr.rtk.ins,&svr.rtk.opt.insopt,&imud);
 //
 //        /* zero velocity/zero angular rate update */
 //        ecef2pos(svr.rtk.ins.position,pos);
diff --git a/TC_NAV_Zjut_post/Src/real_time/nhc.c b/TC_NAV_Zjut_post/Src/real_time/nhc.c
index a004dc9..8eb7ed8 100644
--- a/TC_NAV_Zjut_post/Src/real_time/nhc.c
+++ b/TC_NAV_Zjut_post/Src/real_time/nhc.c
@@ -4,7 +4,7 @@
 #include "rtklib.h"
 
 #define MAXVEL      0.5          /* max velocity for using non-holonomic constraint */
-#define VARVEL      SQR(0.3)    /* initial variance of ins velocity ((m/s)^2) */
+#define VARVEL      SQR(0.05)    /* initial variance of ins velocity ((m/s)^2) */
 
 /* measurement sensitive-matrix for non-holonomic----------------------------*/
 static int bldnhc(const insopt_t *opt,const imud_t *imu,const double *Cbe,
@@ -44,7 +44,7 @@ static int bldnhc(const insopt_t *opt,const imud_t *imu,const double *Cbe,
             trace(2,"too large vehicle turn\n");
             continue;
         }
-        H[IA+nv*nx]=T[i]; H[IA+1+nv*nx]=T[i+3]; H[IA+2+nv*nx]=T[i+6];
+        H[IA+nv*nx]=-T[i]; H[IA+1+nv*nx]=-T[i+3]; H[IA+2+nv*nx]=-T[i+6];
         H[IV+nv*nx]=C[i]; H[IV+1+nv*nx]=C[i+3]; H[IV+2+nv*nx]=C[i+6];
 
         v[nv  ]=vb[i];
@@ -67,8 +67,8 @@ extern int nhc(ins_t *ins,const insopt_t *opt,const imud_t *imu)
 
     trace(3,"nhc:\n");
 
-    H=zeros(2,nx); R=zeros(2,2);
-    v=zeros(2,1); x=zeros(1,nx);
+    H=zeros(nx,2); R=zeros(2,2);
+    v=zeros(2,1); x=zeros(nx,1);
 
     nv=bldnhc(opt,imu,ins->Cbe,ins->velocity,nx,v,H,R);