Creating Shapes Using Gestures (MathDraw)

The MathDraw tool lets you use touchscreen or mouse gestures to create points, lines, circles, and other shapes.

MathDraw is available in:

• Geometry view without the analytic window displayed.
• Graphing view when the x scale and y scale are identical. This avoids non-circular ellipses and non-square rectangles appearing as circles and squares.

MathDraw is not available in the 3D Graphing view or in the Geometry view with the analytic window displayed.

Activating MathDraw

1. If using the Geometry view with the analytic window visible, use the View menu to hide the window.
2. On the Actions menu, select MathDraw.

The MathDraw icon appears. You can begin using the tool.

Canceling MathDraw

▶ When you have finished using the MathDraw tool, press Esc.

The tool also closes if you select a different tool or change views.

 

To create a labeled point, tap or click in an open area.

• If the point is close to an existing line, segment, ray, geometric conic (including circles), or polygon, the point snaps to that object. You can also place a point on the intersection of any two of those types of objects.
• If the point is close to a visible grid location in a Graphs view or the analytic window of a Geometry view, it snaps to the grid.

 

To create a line or segment, touch or click the initial position, and then drag to the end position.

• If the drawn line passes near an existing point, the line snaps to the point.
• If the drawn line starts close to an existing point and ends next to another existing point , it becomes a segment defined by those points.
• If the drawn line is nearly parallel or perpendicular to an existing line, segment, or side of a polygon, it aligns to that object.

Note: The default tolerance for detecting parallel/perpendicular lines is 12.5 degrees. This tolerance can be redefined using a variable named ti_gg_fd.angle_tol. You can change the tolerance in the current problem by setting this variable in the calculator app to a value in the range 0 through 45 (0=no parallel/perpendicular detection).

 

To create a circle or ellipse, use the touchscreen or mouse to draw the approximate shape.

• If the drawn shape is sufficiently circular, a circle is created.
• If the shape is elongated, an ellipse is created.
• If the virtual center of the drawn shape is near an existing point, the circle or ellipse is centered on that point.

 

To create a triangle, draw a triangle-like shape.

• If a drawn vertex is close to an existing point, the vertex snaps to the point.

 

To create a rectangle or square, use the touchscreen or mouse to draw the perimeter.

• If the drawn shape is nearly square, a square is created.
• If the drawn shape is elongated, a rectangle is created.
• If the center of a square is close to an existing point, the square snaps to that point.

 

To create a polygon, tap or click a succession of existing points, ending on the first point you tapped.

 

In the Graphs view, MathDraw attempts to recognize certain gestures as functions for analytic parabolas.

Note: The default step value for quantization of the parabola coefficients is 1/32. The denominator of this fraction can be redefined using a variable named ti_gg_fd.par_quant. You can change the step value in the current problem by setting this variable to a value greater or equal to 2. A value of 2, for example, produces a step value of 0.5.

 

To measure the angle between two existing lines, use the touchscreen or mouse to draw a circle arc from one of the lines to the other.

• If the intersection point between the two lines does not exist, it is created and labeled.
• The angle is not a directed angle.

 

To create a point midway between two points, tap or click point 1, point 2, and then point 1 again.

 

To erase objects, use the touchscreen or mouse to drag left and right, similar to the motion of erasing a whiteboard.

• The erasure area is the bounding rectangle of the erasure gesture.
• All point objects and their dependents inside the erasure area are removed.