gtsam用isam发生Thrown when a linear system is ill-posed. The most common cause for this error is having underconstrained variable

发生错误的时候

1.检查key的格式  递增是否正确

2.检查noise model有没有设置对

3.pose发生了很大的变化，一般是位姿没哟设置对造成的。