Automatic Push Button Parking from Ford

The question is straight. Whether it is better to use a sensor powered park assist or a camera assisted parking system. In many car park assist system it involves or uses both the camera and sensor help but I want to know whether the use of sensor or camera alone can give a exact park assist? I had used an android app in which camera should be pointed to an object to measure the distance of the object from us .But the app failed to calculate the distance correctly. So I want to know whether can we measure the distance of an object by using an camera?(The app used is named as “Smart tools’’).So If the camera can not be sued in distance measuring process, It will not be fit for auto car park.Is sensor more reliable in assisting?Do cameras help in manual parking alone or they have other applications?