GPS Heading question

I have a difficult time to understand “the GPS heading will remain constant in relation to the Field, regardless of the starting position of the robot”. Would you please give me an example to help me understand it? Thanks.

Let’s say you start diagonally on the field, touching the match load bar in all points (so 45 degrees). A GPS sensor will return the ABSOLUTE heading and return 45 degrees in that scenario. However, an inertial sensor will return 0 degrees when it is calibrated and will give the RELATIVE position. It has no way of determining the absolute heading.


One more curious question, if I place the GPS at the back of the robot and the GPS “eye” face back (opposite to the robot head), does the degree returned by the GPS will be 180 degree opposite to the robot heading (eg robot head face to 0 degree)?

Thank you. What I can understand is if the robot’s head face to 90 degree of the field at the end point, the GPS will show 90 degree wherever the robot start from. If the robot turn right again and if its head face to 180 degree, the GPS will show 180 degree. Am I right?
Since inertial sensor will always be calibrated at the start point, so what degree it will return when the robot head face to 180 degree in the above scenario?

The field perimeter is marked with a coded pattern that the gps sensor reads. Imagine one side has a 0 printed in the middle then, printed around the rest of the perimeter are the numbers 1 through 359, evenly spaced such that the 1 and the 359 are both adjacent to the 0.

Heading is the number on the perimeter that your robot is pointed at.


There is lots of useful information in the Knowledge Base:
Note the information about the X/Y and Angle offsets for the sensor.

If the inertial sensor is calibrated when the GPS is showing 90 degrees, and then you go to 180 degrees, the inertial sensor would display 90 degrees.

Configure it in VEXCode Pro like this or use other methods for other coding platforms (though mostly similar.) This allows you to specify the placement of the GPS. For example, if it is facing backwards, you would set it up like above and the graphic will help you.

1 Like