Concept: Turtle Position

Turtles don't really move from patch to patch. They actually move on a real number grid, and Starlogo approximates where they are by displaying them on the patch they are "in". For example, if a turtle is actually at position (1.5,1.5) it will be displayed at patch position (2,2).

Checking and Resetting Turtle Position

We've already seen that you can reset a turtle position with the forward command. In addition, you can check a turtle position with the properties xcor and ycor, and use setx, sety, and setxy to reset these positions.

Note: The Wonderful Turtle Monitor!

Don't leave home without this facility. You can monitor the change in the properties of a particular turtle by double clicking on it and bringing up a turtle monitor window. Try doing this first, then monitor the change in turtle position while you explore.

Explorations

• Go to the settings... menu and change the screen size to 101 and the patch size to 4x4.
• Create 1 turtle. Where is it placed? What is its heading?
• Set the heading to north and move forward 50. Where do you expect the turtle to be?
• Set the heading to 45 degrees and move forward 50. Where do you expect to be? How many steps do you expect to take to be in the corner? See if you can compute the result mathematically.
• Set the heading to north and move forward 80. Where is the turtle? Why?
• When you move north, east, south, or west, how many steps does it take to get back to the center?
• How can you move a turtle diagonally one full patch at a time?