A device for determining relative orientation between two different locations, i.e. for determining the relative orientation between two different coordinate systems each associated with a respective different location, said device comprising: an imager; an inertial orientation sensor, firmly attached to said imager, adapted to determine information relating to the orientation thereof, said inertial orientation sensor exhibiting drift; and a processor coupled with said imager and with said inertial orientation sensor, said processor adapted to determine a first orientation measurement of said device, according to information related to an orientation of said inertial orientation sensor, when said device is oriented with a first orientation indicator and adapted to determine a first time-tag associated with said first orientation measurement, said first orientation indicator being located at a first location, said processor adapted to determine a second orientation measurement of said device, according to information related to an orientation of said inertial orientation sensor, when said device is oriented with a second orientation indicator and adapted to determine a second time-tag associated with said second orientation measurement, said second orientation indicator being located at a second location, said processor adapted to determine a third orientation measurement of said device, according to information related to an orientation of said inertial orientation sensor, when said device is oriented again with said first orientation indicator and adapted to determine a third time-tag associated with said third orientation measurement, said processor adapted to determine the drift associated with said inertial orientation sensor according to a difference between said first orientation measurement and said third orientation measurement, and the respective time-tags associated with said first and third orientation measurements, said processor adapted to determine an angle difference between said first orientation indicator and said second orientation indicator according to said first orientation measurement and said second orientation measurement, said first and second time-tags and said drift, wherein each of said first orientation indicator and second orientation indicator is one of a Boresight Registration Unit and at least three Light Emitting Diodes, wherein, said processor is adapted to determine when said device is oriented with said first orientation indicator according to at least one image of said first orientation indicator acquired by said imager, wherein, said processor is adapted to determine when said device is oriented with said second orientation indicator according to at least one image of said second orientation indicator acquired by said imager. an imager; an inertial orientation sensor, firmly attached to said imager, adapted to determine information relating to the orientation thereof, said inertial orientation sensor exhibiting drift; and a processor coupled with said imager and with said inertial orientation sensor, said processor adapted to determine a first orientation measurement of said device, according to information related to an orientation of said inertial orientation sensor, when said device is oriented with a first orientation indicator and adapted to determine a first time-tag associated with said first orientation measurement, said first orientation indicator being located at a first location, said processor adapted to determine a second orientation measurement of said device, according to information related to an orientation of said inertial orientation sensor, when said device is oriented with a second orientation indicator and adapted to determine a second time-tag associated with said second orientation measurement, said second orientation indicator being located at a second location, said processor adapted to determine a third orientation measurement of said device, according to information related to an orientation of said inertial orientation sensor, when said device is oriented again with said first orientation indicator and adapted to determine a third time-tag associated with said third orientation measurement, said processor adapted to determine the drift associated with said inertial orientation sensor according to a difference between said first orientation measurement and said third orientation measurement, and the respective time-tags associated with said first and third orientation measurements, said processor adapted to determine an angle difference between said first orientation indicator and said second orientation indicator according to said first orientation measurement and said second orientation measurement, said first and second time-tags and said drift, wherein each of said first orientation indicator and second orientation indicator is one of a Boresight Registration Unit and at least three Light Emitting Diodes, wherein, said processor is adapted to determine when said device is oriented with said first orientation indicator according to at least one image of said first orientation indicator acquired by said imager, wherein, said processor is adapted to determine when said device is oriented with said second orientation indicator according to at least one image of said second orientation indicator acquired by said imager.