# How scan angle is measured and published in LaserScan msg?

Range of the distance of the obstacles are measured from output of laser sensor but how actually the scan angles are measured. do we use any separate sensor to get the value?

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The scan angles depend on the angle_increment and angle_min values stored into the topic (as you can see here). i.e.: if angle_increment is set to 0.1 (rad) the first range measurement is refered to angle_min + 0*0.1 , the second to angle_min + 1*0.1 rad, the third to angle_min+2*0.1 rad and so on. In general, the angle refered to a particular range measurement is

angle = angle_min + index*angle_increment


where index is refered to the index of the vector's element containing that range measurement.

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The scan angle is relative to the laser, where the laser is by definition at the frame that is defined for the driver instance. E.g., for 0 deg and 1m, there will be a point at x=1m in the laser frame.

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Laser is emitted by transmitter for every 1 or 0.5 degree depending on your laser setting.

Corresponding distances were calculated using time taken by laser pulse to reflect at receiver.

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