Origin of a Point Cloud

Wikipedia has defined a “Point Cloud” as “a set of data points in some coordinate system”. In a three-

dimensional coordinate system each point is commonly defined by an X, Y, and Z value, and is often employed to represent the surface of an object. Point cloud geometry is often referred to, rather mistakenly, as LiDAR. LiDAR is a technology that can be used to make point clouds; so measurements produced with LiDAR technology is more aptly known as LiDAR data. Most commonly, point clouds are the result of data being output by 3D scanners. Aerial and Terrestrial LiDAR sensors are two such examples of 3D scanners that perform a large number of measurements on an object's surface to output a point cloud, but as you’ll read, point clouds may originate from various other sources and technologies.

Photogrammetric Detection and Ranging (PhoDAR) is an alternative technology to conventional photogrammetry and LiDAR to generate point clouds. Though, PhoDAR and LiDAR are both capable of producing point clouds, the primary difference being PhoDAR uses photographic data (i.e. pictures) collected with a camera to generate a point cloud, whereas LiDAR involves the collection of data measured directly from the reflection of an object using a laser.

Another technology from which topographical point clouds are regularly created is IFSAR (Interferometric Synthetic Aperture Radar). . IFSAR sensors are typically flown in fixed-wing aircraft or mounted to satellites, and primarily uses X-band data of the electromagnetic spectrum to perform measurements. IFSAR data collection involves placing two radar (radio detection and ranging) antennas on the vehicle such that one antenna transmits a radar beam, and then both antennae receive the radar beam reflected from the target (usually the earth’s surface). Captured signals are combined with aircraft telemetry and positional data are processed to generate an interferogram, which is employed to generate elevation products.

Sound Navigation and Ranging (SONAR) technology uses the propagation of sound in an underwater environment to target objects. It is most commonly used to in the surveying profession to determine water depth (bathymetry). Sonar is applied to water-based activities because sound waves attenuate (taper off) less in water as they travel than do radar and light waves.

In future posts I’ll provide detailed analysis of the pros/cons, uses, and accuracies of the various technologies, but for now, the following table provides a brief overview of each.

Technology	Coverage	Accuracy	Use of Technology
Terrestrial LiDAR (Mobile or Static)	Small-to-Medium area projects	1cm	Buildings, Corridor mapping, Asset Inventory, Engineering Design
Aerial LiDAR	Large area projects, in varied terrain conditions	10 cm	Flood plain mapping, Disaster Management, Transportation and Engineering design, Impervious surface mapping, vegetation mapping
PhoDAR	Medium-area projects	15+ cm (dependent on GSD)	Same as above
IFSAR	Large area projects in varied terrain conditions	30 cm	Same as above
SONAR	Small-to-Medium area projects	5-10cm	Underwater studies, dredging, navigation

Cheers!
Srini

Article: LiDAR Fusion for Impervious Surface Mapping

With the deployment of our 2 brand new Lynx SG1 systems, the past month has been admittedly hectic.  Although we haven’t had much time lately to post new material to the Blog, our team continues to contribute to the profession through other media outlets.

Check out a recent article published in the May edition of LiDAR News Magazine that was authored by our own Dr. Srinivasan Dharmapuri and Aaron Morris.

Cheers!

Stephen

Best Practices

While mounting our Mobile LiDAR spring offensive, I didn't have much time to prepare articles for LiDAR News, much less update and maintain the blog.  Therefore, my colleague Dr. Srinivasan Dharmapuri stepped up and prepared an article on Best Practices for Mobile Mapping System Data collection and Processing.  Dr. Srini, Baker's resident LiDAR Scientist, has served on the ASPRS Mobile Mapping Committee since it's inauguration and is an integral part of our LiDAR organization.

Should you have recommendations for what you would like to see on the blog, in a more detailed article, or just a question to "Ask the Doctor," please leave a comment.

Cheers!
Stephen

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

SAE 2011 Autonomous Vehicle Symposium

Baker’s resident LiDAR Scientist, Dr. Srinivasan “Srini” Dharmapuri,  was a featured presenter at the Society of Automotive Engineers (SAE) 2011 Autonomous Vehicle Symposium, held at Carnegie Mellon University (Pittsburgh, PA) on 8/10/11. The symposium showcased smaller and more focused discussions on innovative drive assist and autonomous vehicle technologies in transportation, agriculture resource management, construction and mining.  Srini’s presentation conveyed the advantages and uses of Mobile LiDAR technology, and  highlighted several case studies performed by Baker in the Transportation arena , including roadway design, rail transit, and bridges.  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. As mentioned in an earlier posting, Srini is the Vice Chair of the ASPRS Mobile Mapping Committee.  Perhaps he can provide an update on the committee's activities in the near future.

 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

Ask the Doctor

We would like to welcome a new member to our LiDAR team.  Dr. Srinivasan “Srini” Dharmapuri is a 25 year veteran of the geospatial sciences, and has extensive, wide-ranging experience within the Geospatial industry; most notably with LiDAR, Photogrammetry, and GIS. He has worked in both the private and public sectors, as well as internationally.  In addition to his educational achievements, Master’s of Science (Physics), Master’s of Technology (Remote Sensing), and Doctorate (Satellite Photogrammetry), Srini is also an ASPRS Certified Photogrammetrist and licensed Photogrammetric Surveyor in South Carolina and Virginia, as well as a Certified GIS Professional.

The Doctor is In

Srini will have a regular presence on the blog with a new segment called "Ask the Doctor".  He will answer questions presented from readers that may not be covered in the Frequently Asked Questions section of the blog.  Should you wish to have a question answered by the doctor, please leave a comment or send our team an email (see "Who We Are" tab).

Welcome Dr. Srini! It's nice to have you as part of our team!

Stephen