GPS World, January 2013

ADVERTORIAL Beyond General Receiver Specifications T he in depth specifications presented in this GNSS receiver survey are critical for making the correct purchase decision however specifications must always be considered in relation to the demands of your application Buyers must consider matters of size weight accuracy and availability and weigh them in light of other factors such as cost and ease of integration As well certain aspects of a GNSS receivers functionality may not be directly comparable by considering receiver specifications alone When choosing your GNSS provider consider the following to ensure you optimize your GNSS receiver purchase Absolute Accuracy versus Relative Accuracy The receiver survey displays the absolute positioning accuracy of the various receivers but for some applications this is not the only quality that matters In traditional GNSS applications such as surveying absolute position accuracy is critical Precision farming and machine automation require position output that is also very stable over time GNSS p position accuracy can vary over time with changes in satellite visibility or when the receiver changes b between correction types These changes can result in position solution discontinuities Receivers vary greatly in how they deal with these shifts When choosing a receiver for your application enquire about the receivers relative position stability to ensure that the receiver will suit your application NovAtels GL1DE and mode match algorithms are specially designed to ensure the position from the receiver is as smooth as possible regardless of the challenges presented by the operating environment Heading and Orientation Determination GNSS are by their nature position determination systems However many applications such as excavating and drilling aircraft and marine vessel navigation mobile or airborne mapping require accurate orientation information as well which single antenna GNSS systems cannot easily provide Direction of travel can be used as an approximation of heading but true vehicle heading roll and pitch must be derived using an alternate approach There are multiple ways to work around this limitation of GNSS Heading can be determined by measuring the 3D offset between two or more GNSS antennas fixed to a vehicle For environments where the GNSS signal availability is good these systems can give a very accurate measurement of the heading and pitch of a vehicle GNSS heading products like NovAtels ALIGN technology can be easily deployed onto a vehicle to provide heading for a range of applications Inertial sensors gyroscopes and accelerometers can also be used along with GNSS to compute a 3D attitude solution roll pitch heading GNSS INS systems have the advantage of computing attitude and also of improving the position reliability of the GNSS receiver NovAtels tightlycoupled SPAN GNSS INS technology is available on all our OEM6 receivers SPAN offers a range of IMUs to suit many applications requiring highrate robust positioning and precise attitude Raw Data for Post Processing High precision applications usually rely on postmission processing of the GNSS data GNSS post processing offers many advantages over real time operation If a real time solution is not required the raw GNSS measurement data can be collected in the field and processed postmission to provide a precise position and velocity solution Post processing allows for simplified real time system operation without the need for real time telemetry and allows lower cost receiver hardware to be used There are publicly available reference station data or precise satellite clock and orbit data for precise point positioning PPP When choosing a receiver consider how the data James Hamilton GPS World January 2013 www gpsworld com 2