Monday, September 24, 2012

Baker's Dozen: Laws 1 and 2

After I wrote the Baker's Dozen: 13 Laws of Mobile LiDAR , a colleague asked me the question a lot of readers were probably thinking - aren't Laws #1 (Too much is better than not enough) and #2 (Sometimes more is just more, not better) in direct contradiction to one another?

Although at first glance they may appear contradictory, the laws actually describe two uniquely different concepts.

Mobile LiDAR Law #1: Too much is better than not enough. 
The underlying principle of this Law is to develop your collection methodology around the concept that Mobile LiDAR data can be repurposed for other uses/needs; and you NEVER want to make a repeat visit to a jobsite to collect a little more you could’ve captured the first time.  Take for example an interstate project where Mobile LiDAR is used in support of engineering design services for a road surface that is to be substantially undercut for removal and replacement of unstable soils.  

Common among large, multi-staged construction projects, numerous DOT departments and contractors may be involved.  Each group, with its own budget, is likely at varying stages of design or construction, and not necessarily proactively communicating or coordinating activities between groups that could capitalize on cost-savings.  The scope of work issued by Group A may likely only require survey information for the lanes slated for reconstruction - without consideration for the engineering design work needed by Group B for the two crossovers for maintenance of traffic during construction. 

By anticipating Group B’s needs, and simply modifying the scanning trajectory or extent of capture, you effectively create a single dataset that not only meets Group A’s requirements, but also opens the door to re-purpose the data to support Group B – saving time and money for the client.  Obviously not all scenarios are this cut and dry, and you need to be cognizant that you’re not getting too carried away collecting additional data that may not be utilized, but when thoughtfully applied, everybody wins.   

Mobile LiDAR Law #2: Sometimes more is just more, not better. 
When the Laws of Mobile LiDAR were written, Baker was in the process of evaluating an upgrade to an Optech Lynx M1 system - dual 500 kHz sensor heads.  The upgrade would result in a 2.5x increase in the volume of points that we would be capable of measuring.  Although the collection rates would be staggering, would it improve our ability to identify features better? Do something we weren't capable of doing?  Eliminate another process?  After all, the range and scanner rates would not have been any different than our existing sensors, and the 400,000 measurements per second we can currently capture produce amazing resolution and rapid ability to identify features.

As you can review in my latest article on LiDAR News regarding point densities, we left nothing to chance.  Our team evaluated the densities achieved with our system under various conditions and collection practices.  We determined that as we would have more data, not necessarily better.

The Baker's Dozen was written over a year ago and I've read them countless times since.  Each of them still applies today.  After I'm finished writing about each of them, I'll step back and reexamine the list one more time before they're chiseled in granite.


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