How to measure the distance from CAMERA and the object

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Hi all,

i need to measure the distance between the pi camera module and the object , i've found this formula

distance to object (mm) =                                                                                                                                                                       focal length (mm) * real height of the object (mm)   * image height (pixels)
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                          object height (pixels) * sensor height (mm)

but i"m wondering opencv doesn"t implement a function to do this measure ??

thanks :)