An Intro to Mobile Mapping System Trajectories

A 115Kb PDF of the five charts that go with this article is available by clicking HERE

Mobile mapping innovation seems to be everywhere, at least in the 3D LiDAR world.Just a year ago conversations about mobile mapping involved topics like, What is it?, What can you do with it?, or How accurate can it really be? Well, most of these questions have been answered, except for the one about accuracy. Put two surveyors in a room with a tape measure and ask them to measure something. Then ask them to agree on accuracy and precision statements and I think we know what will happen.

The conversations are beginning to take place concerning topics like guidelines, best practices, certification, and error budgets as they apply to mobile mapping. Its this last topic error budgets that I would like to focus on today.

Error budgets in mobile mapping systems, or for that matter, all kinematic mapping systems are quite different from what most practitioners of surveying and mapping are used to. As measurement professionals we like our observations to be made from very stable, static platforms but that is not the case with kinematic. In fact not only is the sensor moving, but we have to measure not only the position, but we also have to know the sensor orientation.

What this means for those who are concerned about certifications and calibrations of the data is that we have left the nice clean and comfortable world that most of us are used to, time independent solutions, and entered the world of time dependent solutions. This world is also known as the navigation solution, or the trajectory.

Understanding the basics of how a trajectory is calculated is fundamental to understanding how to design an error budget for a kinematic mapping project. This can be a deep and complicated topic, if you let it. But we dont have to go that far. Just a little bit of understanding into the process can help someone understand why solutions from kinematic mapping systems can vary from project to project.

Specifying mobile mapping is much more than requiring a factory certification of the instruments and their calibration. Understanding that a perfectly calibrated and certified system is capable of producing varying qualities of navigation solutions is essential. The trajectory solution is as important as all the specifications and certifications that you can provide.

To that end, Ive put together a slide deck that I refer to as A Kindergarteners Guide to Trajectory Solutions. Its not a robust mathematical derivation; analytically its somewhat inconsistent and has left out steps and details. But what is does do is explain, at an introductory level what is happening in the black box. It shows that the opened ended item in the error budget we call trajectory does not have to be a blank check. Instead it is the area that will allow this technology to explode into maturity. If we get this right, mobile mapping can be as common as RTK GPS is today.

A 115Kb PDF of the five charts that go with this article is available by clicking HERE