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Using pi in an URDF file

asked 2017-11-30 11:18:46 -0500

MatthiasLoebach gravatar image

We want to use the value of pi in an URDF file, since we have to rotate a model by 90 degrees. Is there any builtin macro for pi in URDF? At the moment we are simply using our own M_PI macro, but it would be nice to know what the intended way of doing such a thing would be.

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answered 2017-11-30 13:18:35 -0500

updated 2017-11-30 13:20:28 -0500

You can do this with xacro (a XML macro language):

From section 3. Math Expression

Since ROS Jade, Xacro employs python to evaluate expressions enclosed in dollared-braces (${}). This allows for more complex arithmetic expressions. Also, some basic constants, e.g. pi, are already predefined:

<xacro:property name="R" value="2" />
<xacro:property name="alpha" value="${30/180*pi}" />
<circle circumference="${2 * pi * R}" pos="${sin(alpha)} ${cos(alpha)}" />

You might be interested in the ROS xacro tutorial

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Asked: 2017-11-30 11:18:46 -0500

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Last updated: Nov 30 '17