Mobile LiDAR Law #4

Consistency counts; stop guessing.

Sample GPS Observation Log utilized by Baker

Perhaps the 4th law of the Baker's Dozen was inspired by my early years in the surveying profession.  I spent vast amounts of time collecting and processing static GPS for developing project specific and county-wide geodetic control networks. At each monument, we were required to record detailed information on a GPS observation log sheet.  These sheets were utilized in post processing to validate antenna heights (recorded in feet and meters as further validation), input station number, and identify possible obstructions. An incorrect antenna height was usually the primary suspect in a bad baseline solution.  I quickly became a fan of fixed-height tripods.  Although at that time they were clumsy and didn't collapse, they minimized or eliminated Scribner's errors and second guessing.

Similar opportunities for inconsistencies to present themselves exist with Mobile LiDAR collection. We employ various methods and procedures to ensure successful collection - outlined in Law #7 - Applied Control.  Our crew regularly deploys static GPS base(s) for SBET post-processing.  For consistency, we utilize two meter fixed height tripods and record base information on a GPS log sheet.  However, due to the complexity of a collection and equipment utilized, there are additional areas where consistency matters.

System Start-up and Collection

The successful start-up and operation of our Mobile LiDAR unit requires a process - it's not as simple as pushing a button and collecting LiDAR data.  Our crew follows a carefully scripted procedure to start, setup, and perform a collection.  From time-to-time our equipment manufacturer also provides updates to these procedures in the form of Customer Advisories.  These steps must be followed to identify the root cause of a problem should one occur - see Law #12. Similar to the observation log, we capture information relevant to the collection to ensure all areas are covered.  The information includes tire pressure, ambient temperature, weather conditions, and other factors - much like a traditional survey crew.

By taking copious notes, we have a record of field activities and conditions.  We are consistent with the way our crew functions, which removes any guessing.  

Cheers!

Stephen

Picture of the Week

The image I posted two weeks ago created some good natured discussion regarding allegiances.  As Baker is based in Pennsylvania, I work with a lot of people who do not share my rabid devotion to a certain SEC University.  In order to appease my colleagues to the north, I quickly pulled together some publicly available Aerial LiDAR data and imagery.  Below is a colorized point cloud of the PSU campus. With the PAMAP program, there are great datasets available.

Have a good weekend.

Cheers!
Stephen

Top 3 Posts

If you're relatively new to Baker's Mobile LiDAR blog, you may not know that it's something we've been doing for about three years now.  In that time, there have been a few that have hands down attracted more attention than others.  Perhaps the reasoning is that older posts have had more time to attract pageviews.  However, our number one viewed blog was written nearly a full year after number 2 and 3.

#1:  Modeling Bridges from Mobile LiDAR Information
In this posting written in October 2010, I illustrate how three-dimensional modeling and rendering is performed from information collected for an interstate corridor.  The mapping was completed by Baker's Applied Technologies Group using MicroStation.

#2:  To Debunk or Not To Debunk - That is the Question

One of our earliest postings was derived from one of our first collections - performed just 4 days after the installation of our system.  We were in central PA attending a corporate meeting.  While checking into our hotel, we noticed the rack of brochures for area attractions.  One was for Gravity Hill - a local attraction where: "Cars roll uphill and water flows the wrong way. It's a place where gravity has gone haywire."  We collected the hill, but the data resides on a hard drive on my shelf left unprocessed while the mystery remains unconfirmed.

#3:  Measuring Systems Part 1 - Positioning

Again, another posting from 2009 earns a top spot.  As our blog was taking shape, it was important to talk about the equipment and how it performs.  In this posting, I discuss the positioning systems on the vehicle:  GPS, IMU and DMI.  It has gained a lot of attention as did a similar article written for LiDAR News titled:  Mobile Positioning Systems.   

I hope you have the time to review some of our earlier postings.  I like to revisit things we've done in the past just to see how far we've come.

Cheers!

Stephen

Law #7: Applied Control

In an article last year, I wrote extensively about Law #7: The data you capture is only as good as the applied control.  And earlier this year, I addressed the topic again with a posting titled:  Control Plan - Art or Necessity?  The survey methodologies employed for establishing, locating and quantifying ground control are all important factors to successfully perform a Mobile LiDAR collection; however, as equally important, are the controls (techniques, processes, QA routines, etc.) applied by the collection staff, processing team and project manager throughout the project lifecycle. Today’s discussion focuses on the controls applied by our collection staff; while future posts will address processing and project management.

Since day 1, Baker has been developing our Standard Operating Procedures (SOP).  These procedures are not chiseled in granite like The Baker's Dozen, but rather are constantly evolving with new techniques, software, hardware and client requirements.  We have modified the documents countless times to implement changes, educate operators and ensure consistency.  Our SOP's include, but are not limited to:

• Collection Planning - from GPS to driving routes
• System Startup and Shutdown
• Field Notes
• Data Extraction
• Preliminary Processing
• QA/QC
• Data Transmittal

The above SOP's are but a handful of the controls we apply on a daily basis to ensure overall project success.  Well-constructed SOP’s provide the framework for consistent results; and ultimately result in quality products and a satisfied client.

Cheers!

Stephen

Picture of the Week

Although my alma mater, the University of Florida, has a bye week, I thought I'd share the Mobile LiDAR picture of the week.  I've had this for some time, but in the spirit of college football season, here it is...

Go Gators!
Stephen

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.

Cheers!
Stephen

Mobile LiDAR Point Density - Part 2

I've had a brief hiatus from the blogosphere while working on a project that kept me out of town for a few weeks.  I usually do not travel with the system since our collection team is quite capable of anything I throw at them quite honestly.  However, the most recent mobilization was truly unique as you'll come to find out in future posts - can't share too much, yet.

Gene Roe, Managing Editor of LiDAR News, was successful in getting another article from me for the regular newsletter.  My latest contribution is a continuation of a previous topic and is titled:  Mobile LiDAR Point Density - Part 2.  I discuss how the following variables influence density:

• Vehicle speed, measurement frequency, and scanner rates;
• Angle of incidence and the impact of flat surfaces;
• Distance to target and effect of rotated sensors; and
• Collection paths and moving obstructions.

The images from the article are provided for a little more clarity. 

The image represents 3 passes along the same stretch of a 2 lane residential road. The data was collected at 25 mph with a scanner rate of 120 Hz. The three images show results of collecting at laser frequencies of 75 kHz, 100 kHz and 200 kHz – from left to right.

Using the vehicle speed and scanner rate, we can calculate the line spacing - the distance between lines of LiDAR points laid down on the surface.

The image above shows the data captured from one sensor along the centerline of a runway.  The data tapers off rapidly due to the limited backscatter caused by the flat surface. The point density on the pavement stripes at the extents is increased to to the material.

I will have one last article in the series next month.  It will focus on the resolution required to identify objects and tools that are available for feature extraction which utilize photography.

Feel free to leave a comment if there's a topic you would like to read about.

Cheers!

Stephen

LiDAR Point Density

Recently, I prepared an article for LiDAR News.  The purpose of the article, Mobile LiDAR Point Density, is to serve as an introduction to LiDAR point densities.  Whether from a static, mobile or aerial system there are various influences to point density or nominal point spacing.

A portrait of our founder Michael Baker Jr. hangs in our conference room. Here, a static scan with a horizontal and vertical resolution of 0.005’ at 30’ is shown. The image represents approximately 1,375,000 points and was collected using a Leica ScanStation 2.

The above image represents a colorized point cloud of an Aerial LiDAR capture - utilized collected orthophotography to perform the colorization. The collection was planned and executed to achieve a point density greater than 20 ppsm. 

There will be additional parts to the topic of point density.  The next will focus on the influences related to Mobile LiDAR densities.  While following articles will examine tools that assist in feature identification and exploitation of the point cloud and imagery.

Cheers!
Stephen

Esri International User Conference

Baker, together with RBF Consulting, a Michael Baker Company, will be exhibiting at next week's Esri International User Conference in San Diego.  Baker & RBF staff will be on-site to discuss the many services our Geospatial Information Technologies Practice Area provides.

Our Mobile LiDAR group will be well represented by Bob Hanson, Senior Vice President of GIT, Aaron Morris, Program Manager and Stephen Clancy, Technical Manager.  If you are a reader of the blog and will be attending, please stop by booth #2017.

Also, as Silver Sponsors, Baker is presenting GIS Jeopardy—play and Win! on Tuesday, July 24th from noon to 1:00 PM in Room 14A.

I hope to see you in San Diego next week.

Cheers!
Stephen

Mobile LiDAR in the News

Baker's own Aaron Morris has prepared an article for the July 2012 issue of Professional Surveyor Magazine.  The article, titled LiDAR on the Tracks, discusses the Mobile LiDAR collection and processing of the Keystone Corridor - a 105-mile high speed rail corridor.  The project spanning from Philadelphia to Harrisburg, PA was completed last year.

The hi-rail equipped vehicle is pictured here at Parkesburg Station.  One of only a few locations  between Harrisburg and Lancaster to get off the track, we used the time waiting for a train to pass to grab a hot cup of coffee from WaWa.

I hope you enjoy the article.  Please leave comments or questions for Aaron here.

Cheers!
Stephen

PA-MAPPS Grand Award Winner

Baker's Bob Hanson, Senior Vice President of the
GIT Practice Area is on-hand to accept the award.

At the PA GIS Conference held this past May, Baker received the Grand Award in the 2012 PA-MAPPS Geospatial Products and Services Excellence award competition.  The Keystone Corridor Improvement Program (KCIP) - Mobile LiDAR project included collection of 105 miles of high-speed rail corridor from 30th Street Station in Philadelphia, PA to Harrisburg, PA.  Over the past several months, portions of the project have been included in various posting on the blog:

• Data Fusion: Mobile and Aerial LiDAR
• Riding the Rails
• Mobile LiDAR: Law #13

Although the collection was performed over a year ago and processing was completed shortly thereafter, we continue to utilize the data.  As I'm writing this blog, we are in the process of re-purposing the data for information at 4 additional locations along the corridor.  It hits right at the heart of a posting written by Jonathan Soulen:  Re-Purposing the Cloud.

Cheers,

Stephen

Mobile LiDAR: Law #12

When the system encounters issues, take a breath and reboot

We have all been there; out in the boondocks with only a small section remaining to complete the days’ collections, then almost seemingly on cue, your equipment malfunctions.   Frustration sets in as you see your optimal collection window rapidly dissipating; and the last thing you want to do is waste half of the next morning to re-establish base-stations and calibrate the system, just so you can scan a miniscule segment of corridor, break down the base-stations, and backtrack to where you should’ve already been.

Murphy always seems to have a way to rear his ugly head, and Mobile LiDAR systems have a lot of individual, interconnected components that could fail.  Anyone that uses a computer has undoubtedly experienced unknown fatal errors that can halt productivity and drive you insane (just recently it wasn't the Mobile LiDAR system but a lovely Windows Blue Screen of Death that halted collection); now increase those complexities by a magnitude of six, and you start to get a sense of what a Mobile LiDAR operator can experience.  Unlike in the office environment, Mobile LiDAR failure points are not merely limited to the computer; there’s also the DMI, IMU, Control Rack, GPS (both on-board and base-stations), cameras, lever arms, a plethora of cables, and in the immortal words of Dr. Evil, “frickin’ laser-beams!”

If you’re lucky, an error report or warning will give you a good indication of where the problem occurred, and where you need to begin your examination, but that brings in the infamous “T” word – Troubleshooting.  A singular word that can instantly drive a cold shiver up the spine of any seasoned manager, and a resulting process that can single-handedly destroy your project schedule, or worse, the budget.  Sure, you could classify any activity to remedy an error or issue (especially the easy fixes) as a troubleshooting activities, but to me, “real” troubleshooting typically means “we have no idea what caused the problem, and we’re going to attempt various procedures, that likely won’t work, in a hope we narrow in on the problem”.

Inside the LYNX control rack.

In the heat of the moment, as you’re scrambling to find a solution, don’t let the frustration level build to the point where you blow a gasket and throw a tirade so animated your co-worker feels compelled to record it and post it online.  Nothing good can result from that video going viral and ending up on Tosh.0.  The old adage that sometimes you “lose sight of the forest for all of the trees” can certainly apply.  Step back, take a deep breath, clear your head, and look at it from a different perspective.  Electronics and field equipment can be very finicky sometimes; not to mention introduction of the occasional human error.  Regardless of whether the problem was initiated by a mechanical, or electrical, or a loose nut between the seat and the keyboard, sometimes all you need is that wondrous and magical cure-all…a reboot.

Cheers!

Aaron

Control Plan – Art or Necessity?

We like to think that the proper implementation of ground control, especially when you consider all factors (including cost), is more of an art than just a necessity.  Sure, anyone that has a basic understanding of the technology and general requirements could develop a control plan, but it’s likely to be either over-engineered (resulting in significantly higher cost), or insufficient to meet the true project requirements; higher costs and possibly additional field visits.  A quality control plan should create efficiencies across the board. 

Detailed Mission Planning efforts are a key component to the success of any field survey.  Mission Planning efforts for Mobile LiDAR surveys also include a concerted focus on required ground control.  Project requirements ultimately drive the implementation of control, but there are a myriad of factors and options that must also be closely considered. 

Control layout for a 4-lane divided highway.  Additional control is placed as the bridge to account for GPS outage.

The design and layout of a proper control plan needs to address: client requirements or standards, driving speeds, site access restrictions/limitations, sensor orientation, staff safety, localized obstructions (traffic, vegetation, elevated or sunken roadways, etc), style/type of target, terrain, control point spacing, and processing software limitations among others.  A control plan specialist is an integral part of the project team.  Their decisions and interpretation of local conditions could dictate the overall success or failure of the mission.  

The control layout for a city-wide Mobile LiDAR collection.  

A control plan specialist is an integral part of the project team.  Their decisions and interpretation of local conditions could dictate the overall success or failure of the mission.

Cheers!

Stephen

Mobile LiDAR: Law #3

Hard Drives are Cheap – Time Isn’t

I can sum up Law #3 in two words – Be Efficient!  We make it a requirement for each individual on the team to perform their duties in the most efficient manner, and additionally strive to find better, faster, cheaper ways to perform that work.  But as manager’s we also have to look at initiatives holistically – and sometimes that means creating a little additional work for one group while counteracting that with greater efficiencies for another.

We see this most commonly in collection activities where, just as in real estate, “Location, Location, Location” surely comes to mind.  If there’s any confusion during collection activities about whether a small area should be captured or not, the standing order is undoubtedly to collect it.  An ounce of prevention is better than a pound of cure.  Yes, you are going to have a slightly higher expense for the field crew effort; and yes, data storage is absolutely a concern (especially with systems that are generating 48+ MB of data every second), but external hard drives are inexpensive.

Thankfully, as external storage drive capacity steadily grows, prices continue to fall.  You can run out to a local store and by 1TB of storage for under $100.  I remember back ten years ago when I upgraded my 16MB thumb drive for the new shiny 128MB version.  It was going to solve all of my data-transfer issues for $120.  Today, our LiDAR system would gobble up that device in 3 seconds.  But really it’s all relative.  The same approach to efficiency ten years ago is still perfectly valid today – only now we’re dealing with larger data volumes; and that volume presents other opportunities to enhance efficiencies.

Conventional surveys typically yield just a single-use dataset; but the high resolution and finite detail captured by a Mobile LiDAR survey presents numerous opportunities to re-purpose captured data (see “Re-purposing the Cloud”).  In this method, efficiency gains are not recognized immediately; but if you’ve got the time, and more importantly a projected user, it’s always less costly to leverage your current location and capture the data while you’re already there.

Cheers!
Aaron

Aaron Morris is GIT Operations Manager in Baker's Ridgeland, MS office. In addition to his many daily responsibilities, Aaron also serves as the Program Manger for Mobile LiDAR operations, author and editor.

Point Classification

Baker's latest article for LiDAR News was published last week.  The article, Mobile LiDAR Point Classification, discusses the advantages to classifying features of similar type into groups. The grouping of features into classes provides the ability to isolate, remove or exploit smaller sets of information.  Due to the extensive detail and volume of data provided by Mobile LiDAR, point classification is incredibly useful for downstream applications.

The image above, presented in the article, shows classified features in an urban environment.  Street signs, vegetation, buildings, roads and other information are isolated into user defined classes.

Extents of tree canopies, outlines of building footprints, curbing and overhead wires are clearly depicted in the image above.  Ground points have been removed for clarity.

An elevation of a parking garage with DTM surface shows the undulating terrain.

If you have a recommendation for a future article, please leave a comment. 

Cheers,

Stephen

Thank you to William for helping with content and images for this and past articles.  And, as always, thanks to Aaron for continued support, proofing and guidance.

ASPRS - Presentation on Mobile Mapping

Baker’s resident LiDAR Scientist, Dr. Srinivasan “Srini” Dharmapuri, presented a paper on Urban Surveying using Mobile Mapping and its Related Complexities at ASPRS 2012 Annual conference in Sacramento, CA on 3/22/12.

The conference theme, Imaging and Geospatial Technologies – Into the Future showcased more focused discussions on various geospatial technologies including mobile mapping using LiDAR. Srini’s presentation conveyed the project life cycle for a typical Mobile Mapping/LiDAR project, and highlighted the key complex areas in executing project in urban conditions. The diverse group of international attendees included prominent individuals from the public and private sectors, as well as academia.

As Baker's resident LiDAR Scientist, Dr. Srini is responsible for application development, QA/QC methodologies, technical writing, improving processing efficiency and other related LiDAR (static, mobile and aerial) activities. Also presently, Srini is the Chair of the ASPRS Mobile Mapping Committee involved in arriving at the “best practices document for Mobile Mapping”.

If you have a topic for Srini to write about, please leave it as a comment and we'll include it the Ask the Doctor series.

Cheers!

Stephen

National Surveyor's Week

Three of these men were Surveyors

Tomorrow marks the conclusion of National Surveyor's Week.  It's the time of the year to recognize Surveying as a founding profession - one that was instrumental in defining our country, it's boundaries and infrastructure. As a Professional Surveyor, I take exceptional pride in the profession I've chosen - even more so when discussing the history with people unfamiliar with what we do.

Michael Baker Jr., Inc. was founded as a surveying firm seven decades ago.  And our recent addition to the Baker family, RBF, has a similar legacy.

Perhaps the most personal discovery regarding our history was uncovered during a visit to my wife's grandparents in rural North Carolina.  Unbeknownst to me, it turns out that her grandfather started at Baker in 1943 as a survey rodman.  He worked is way up to run a party before heading off to World War II.  Upon his return from the war, he was offered his job back, but decided to take an alternate route.  He eventually retired from Florida DOT after 40+ years as a bridge engineer.  Upon hearing the story from him, I pulled out my laptop and proceeded to show him Mobile LiDAR data.  To say he was blown away is an understatement.

Poster on display at Baker and RBF offices nationwide.

To my fellow surveying professionals, cheers!  I'm having a pint tonight to celebrate.

Stephen

For more information on the profession and it's history, go to:

American Congress on Surveying and Mapping
National Society of Professional Surveyors
National Museum of Surveying

Like us on Facebook

Some time ago, I created a Facebook page for our operation - an informal place to share photos and other materials in addition to the blog.  Late one evening last week, I applied the new Timeline view to the page and created a URL.  As the days, weeks, months and years pass by, it becomes increasingly more difficult to remember our history.  Hopefully this helps.

I've tasked our crew with providing additional content as they journey about the country. If you're so inclined, Like us on Facebook.

Cheers!
Stephen

Identifying the Need for Mobile LiDAR

In my latest LiDAR News article, I take a stab at how we Identify the Need for Mobile LiDAR for a given project.  I briefly discuss 5 key characteristics to evaluate the use of the technology:

• Level of Detail
• Schedule
• Safety
• Access
• Security

Although there are other circumstances which influence a decision, these key elements are the primary drivers in the process.

Cheers!

Stephen