pfeil <- function(x0,x1,sc1,sc2,pmt,clr){
  vx <- c(x0[1],x1[1])
  vy <- c(x0[2],x1[2])
  vz <- c(x0[3],x1[3])
  lines (trans3d(vx,vy,vz, pmat = rotmat),
         lwd=2, col = clr, lty=1)

  
  x1_pr <- c(x1[1],x1[2],x0[3])
  r <- x1-x0
  r_pr <- r
  r_pr[3] <- 0
# cat(" was ist hier los? r: ",r,"\n")
  r0 <- r/sqrt(r%*%r)
# cat(" was ist hier los? r0: ",r0,"\n")
  s_r <- sqrt(r %*% r)
  s_xy <- sqrt(r[1]^2 + r[2]^2)
#
  r1 <- s_xy^2/s_r
  xh <- (r1/s_r)*r - r_pr
  if (xh[3]!=0) {
    xh0 <- xh/sqrt(xh%*%xh)
  } else {
    xh0 <- c(0,0,1)
  }
#
  p1 <- x1
  p2 <- x1 - sc1*r0 - sc2*xh0
  p3 <- x1 - sc1*r0 + sc2*xh0
  p4 <- p1
#
  xpol <- c(p1[1],p2[1],p3[1],p4[1])
  ypol <- c(p1[2],p2[2],p3[2],p4[2])
  zpol <- c(p1[3],p2[3],p3[3],p4[3])
  polygon (trans3d(xpol, ypol, zpol, pmat = pmt),
          lwd=2, col = clr, border = "red",lty=1)
#
  pfeil <- list(xpol,ypol,zpol)
#  cat(" Ende Pfeil \n")
}