At what speed does a unit that is connected to a GPS-HS GPS Receiver change from using the Heading Sensor to using the GPS derived direction for Course Over Ground?
When the AS GPS HS (GPS and Heading Sensor product) is connected to the unit, the unit uses the Heading information (NMEA HDG) from the heading sensor (digital compass) for the boat icon direction and the Heading Line (if turned on). The GPS Course-Over-Ground (COG) always uses COG derived from the GPS output, not the Heading Sensor. The Course Projection Line always uses the COG derived from the GPS receiver. When only a GPS receiver is connected (internal or external) no heading information is shown. The only direction information is derived from the GPS COG information and the boat icon direction is based on the COG, not Heading (HDG).
Simply stated, Heading and Course Over Ground are separate and are not based on speed and when the heading sensor is connected to the unit the boat icon uses the heading information for its pointing direction and it uses the GPS Course Over Ground information for pointing direction when no heading sensor is connected.