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====== Real plane: Polar curves ======
Polar curves are a special class of plane curves. While in plane curves the x- and y-axes are functions of a parameter, polar curves represent the dependence of the radius curve on the corresponding angle or vice versa. Such curves are often needed when representing directional characteristics.

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{{screen_EN:scr_polar_curve_radius.png}}

While in plane curves two functions depend on a running variable and are referred to as the parameter representation of a curve, in polar curves the two values for x and y are calculated directly from a function. Therefore, only functions containing the variables r, phi and param are permitted, whereby either r or phi may be used. CGRAPH then automatically recognises whether a representation of the radius as a function of the angle (variable phi) or a representation of the angle as a function of the radius (variable r) is desired.

Enter the desired function in the input field for the function, or select one of the existing functions by clicking on the arrow to the right of the input field.

CGRAPH displays flat curves within the range specified for the variable.

After clicking the **//Create graph//** button, CGRAPH switches to the //Display// tab and shows the graph. 

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The default values can be viewed in the tree on the left. Clicking on the (optional) parameter also activates the parameter's adjustability at the bottom. An explanation of this function can be found in the [[OperationParameters|notes on changing the parameter in the graphic display]].
 

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The default values can be changed retrospectively – clicking on one of the values switches CGRAPH back to the tab with the default values. The graphic is adjusted as soon as the **//Create graphic//** button is clicked. Clicking on the coloured symbol for the graph allows you to quickly hide the graphic from the display. Double-clicking on the text allows you to adjust the [[Stroke2D|graphical display]].

The graphic display is in a polar coordinate system. You can switch between this and the Cartesian coordinate system at any time. You will find a description of this in the [[Operating_the_Graphics|notes on operating the graphic display]].

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