Hi,
See this example:
http://wiki.ros.org/rtabmap_ros/Tutorials/SetupOnYourRobot#Kinect_.2B-_2D_laserYou can set this in rtabmap node:
<param name="subscribe_depth" type="bool" value="false"/>
<param name="subscribe_rgb" type="bool" value="false"/>
<param name="subscribe_rgbd" type="bool" value="false"/>
if you don't have a camera.
Well, depending on what you need, using hector slam could be used alone for your application.
cheers,
Mathieu