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nh.getParam("variable", variable in class) will get the values from your launch file or you have to pass the value when you launch your node something like rosrun [package_name] [node_name] [variable="resizing_factor"] (don't use [] that is just for your understanding)

In your case, probably the values are not getting passed while launching the node so it falls in ROS_ERROR. Please try the above method or use a launch file.

For launch file, follow this link: http://wiki.ros.org/roslaunch/XML Refer 5.1 and 5.3 I hope this will help to solve your problem.