Points to Consider for an Aerial Mapping Project

Here are some things to consider when considering using an aerial mapping firm to help you execute your next project. Of course, it goes without saying that you should: 

• only deal with firms that are fully licensed to do business
• work with firms that carry adequate levels of professional liability insurance
• work with firms whose work is performed and managed by highly skilled, experienced and technically proficient professionals

Equally critical is the need for full inclusion in the work process, from development of the work scope, management of personnel, execution of technical work processes, independent review and QA/QC, and delivery of the data to the client.  Other areas include:

Equipment

Aerial mapping is a highly technical profession, and is incredibly hardware intensive, involving planes, helicopters or other aerial platforms, significant investment in hardware for capturing data; be it a film camera, a digital sensor or an airborne LiDAR/digital sensor that is equipped with the latest inertial measurement systems and airborne multi constellation GNSS receiver. All of this equipment is useless without highly skilled technicians to calibrate, maintain and operate it and interpret the data that is collected. The sheer volume of the data collected means the need for robust computer network architecture, high speed computers, a myriad of software and again, the personnel to keep the system running and data flowing efficiently.

Deliverables

Deliverables have shifted from ink on Mylar hand drafted manuscripts, to CAD drawings on CD or DVD, to now routinely shipping multi-terabyte hard disk drives of data to the office for processing and delivery of equally voluminous amount of data to our clients. It is critical to make sure you ask for data that you can use in a technical sense, as well having computers and other hardware that can fully exploit the dataset. 

Please discuss your concerns about data; we can tailor the way we deliver data to you, be it tiling photos and point clouds into smaller sets that are more easily managed, and may allow you to establish a workflow that enables more of your designers or technicians to work simultaneously on a project.

Contact AXIS today today to plan your next mapping project.

HD-LiDAR: Rail Design and Operations

HD-LiDAR: Rail Design and Operations

Airborne LiDAR offers advantages for surveying Rail Infrastructure:

 

• Rail Corridor Design
• Rail Corridor monitoring

Over the past 6 months, AXIS has been providing engineers with top of rail elevations, all catenary information for power lines, vegetation, overpass and tunnel clearances and more transportation features for rail design & monitoring projects. This is all possible through HD-LiDAR technology, which offers: 

• Fast turn-around time from collection to delivery
• safely survey high speed and heavily congested rail corridors, eliminating traffic interference
• Easily map rugged, vegetated, dangerous and inaccessible areas     
  
  

Contact Us today to see a sample LiDAR dataset and the amazing detail available in a single flight!

Vertical Datums

The technical characteristics of vertical datum’s are generally less complicated than their horizontal counterparts. Nationally, two vertical datum’s are in widespread use, National Geodetic Vertical Datum of 1929, or NGVD 29, and the North American Vertical Datum of 1988, typically referred to as NAVD 88. A number of geoid models have been developed over the years to allow determination of orthometric heights, (elevations) using GPS equipment, which have an effect on the accuracy of the values determined, and which must be properly matched to the horizontal datum in use for the project.  There is also a widespread misnomer that the difference between NGVD 29 and NAVD 88 is a fixed amount, which is an absolute falsehood. The difference between the two datum’s varies between zero (0) and nine (9) meters nationally, and just within the boundaries of Delaware from 1.2 at the northern end of the state, 1.1 feet in the Stanton area, makes a very rapid change to only 0.8 feet in Christiana and eventually is as little 0.66 feet in Lewes and 0.7 feet in western Sussex County. It is critical to be aware of this variable amount of difference and model the real difference for each project you undertake. The NGS program Vertcon is a very useful tool to model the difference based on geodetic positions, as is the simpler route of pulling the NGS datasheets for benchmarks around the site and tabulating the differences.

Final Word on NAD 83

The National Geodetic Survey has recently completed its final realization of NAD 83 until they move us to a new datum in 2022. This latest realization, or adjustment to be technically accurate, is identified as NAD 83/2011 Epoch 2010.00 for those operating in the Continental United States, Caribbean and immediate surrounding areas. This adjustment yields some extremely small shifts in positions compared to its predecessors, but also adds a couple very valuable and critical benefits.

• The first of these benefits, and in my eyes the most important, is that finally NGS CORS stations and all the physical monuments we use to “check into” are finally synchronized together, instead of being on two different adjustments, and never brought together to a common reference frame with each other.

• The next critical element, which few people realize, is that the new NAD 83/2011 Epoch 2010.00 can only be used with new Geoid 12A geoid model, due to technical reasons beyond the scope of this article. Older geoid models such as 2009 or earlier do not share a common system of integration and will yield issues in both software and physical measurements on the ground.
  
  
• The third major benefit of the new adjustment is it coincides and is integrated into a revised NGS Datasheet, which includes much more detailed information, not only adjusted coordinates, but also ways to explore what other points are related geodetically to the point on the datasheet, as well as pictures, accuracy predictions and ways to more accurately assess the usefulness of the point for your needs.

The new datasheet does not account for tectonic motion, commonly referred to as velocities, and it is important to realize that the epoch date included in the name of any coordinate system tells you that those coordinates for the point you are standing over is where it was on that date, not necessarily where it is now. A few millimeters a year over a couple decades adds up quick. The need to use a technically competent and up to date professional services consultant is becoming more important every day.