The traditional in-motion initial alignment method
　　obtains the gravity vector in inertial coordinate
　　system twice while
　　parking the land vehicle, and then work out the
　　transformation matrix according to the information
　　obtained. This method sets a limit
　　to the speed and route of vehicle and requires high
　　precision in positioning of coarse alitgnment. In
　　this work, digital map is
　　introduced into the in-motion alignment. With the aid
　　of map matching algorithm, the positioning accuracy
　　is greatly improved in all
　　speeds and routes, which reduces the effect of
　　misalignment angle from coarse alignment for
　　positioning error and improves the
　　accuracy of the in-motion initial alignment. Road
　　tests results show that the integration of digital
　　map and RLG SINS eliminates the
　　requirements of speeds and routes for land vehicles
　　and greatly reduces the effect of coarse alignment
　　for azimuth accuracy. It not
　　only enhances the mobility of land vehicle but also
　　improves the accuracy of initial alignment of
　　inertial navigation system, which is
　　meaningful in real application.