When viewing the directional data for a traffic counter virtual sensor,  you may notice that the directions are labeled COUNT_{OBJECT}_NORTH and COUNT_{OBJECT}_SOUTH. These directions are determined on how the line was drawn.

After adding a sensor line, you will notice that the sensor name (i.e. COUNT_CAR_1) will appear at the end of the line drawn. For example, in the image below the line was drawn from right to left and the sensor name is shown on the left (the end of the sensor line). 

In general, you can assume that the downward direction is going to be the SOUTH direction.

However, there is an exception that if the sensor line is drawn from the lower right quadrant to the upper left quadrant, the south direction will be up in the image. An example of this is shown below, note that the sensor name is shown at the top left, indicating that the line was drawn from bottom right to top left. This is a bug in our sensor implementation and we are currently working to make the sensor direction more intuitive and configurable.