Right Oblique . . . March!

A complex base-mapping project spawns new techniques — and brings the power of oblique imagery to the military.

By Art Kalinski, GISP

When I started basic training and learned the marching command “right oblique march,” little did I know that the term “oblique” would become a capstone of my GIS career. As most readers know, I was a career naval officer who set up the Navy’s first GIS in the mid-eighties. After military retirement and graduate work at the University of North Carolina, I served as the Atlanta Regional Commission (ARC) GIS Manager until I retired early to join Pictometry last year.

I did so because, much to my surprise, oblique imagery was not being used by the military. In Atlanta, we saw such a dramatic improvement in the effectiveness of first responders using oblique imagery that I felt compelled to help bring this technology to our troops in the field. The first major oblique imagery project that I managed was imaging all Marine Corps Bases in the continental United States.

The United States Marine Corps contracted Pictometry International and the engineering firm PBS&J to image every USMC base in the continental U.S. with high-resolution ortho and oblique imagery. The imagery was captured from late 2007 through early 2008 and delivered to Marine Corps headquarters for installation in the East and West Coast GeoFidelis GIS systems. Capturing the imagery was uneventful, except for scheduling flights around base exercises and a solving a technical issue that was keeping us from shooting the high-altitude Marine Corps Mountain Warfare Training Center in Bridgeport, California.

We assisted with the installation of the imagery and software at the East and West GeoFidelis computer centers in a CITRIX environment. After the installation, eighteen user-training classes were held at ten Marine Corps bases.

Students in the USMC user-training classes learned about oblique imagery, the viewing software, and ESRI ArcGIS integration.

The contract also called for a Public Works Implementation Plan and a Fire Protection Implementation Plan. Several other projects — including a 3D interactive model for security use, an oblique mosaic of a base to replace a large wall photograph lost in a major fire, and a proof of concept demonstrating the integration of oblique imagery with TerraGo GeoPDFs — were also completed.

Quality Control

I personally reviewed all the imagery for completeness of coverage, and individual images were spot-checked for image quality. The initial Quantico imagery had too much snow cover to be useful; it was reshot later in the season when the snow had melted. Snow obscures ground details, and the white reflections create excessive contrast that diminishes the visibility of adjoining features.

All imagery from five directions — north, south, east, west, and ortho — had complete coverage, with the exception of the west view imagery of Miramar. Heavy winds had caused the aircraft to drift off course, resulting in a gap in the oblique imagery from the west view. The other views fully cover the two-square-mile area, and although this falls within quality standards, it will be reshot later this year. This is an error rate of only .02 percent.

Technical Difficulties

Oblique imagery had never been collected at the high altitudes needed to photograph the Mountain Warfare Training Center, located about 30 miles east of Yosemite Park. The problem was that the hard drives used to record the imagery couldn’t operate above 10,000 feet. Hard-disk magnetic recorders require a minimal air density in order to separate the record heads from the magnetic media with a microscopic air layer. Low air pressures at 14,000 feet cause the record heads to “crash,” or come in contact with the magnetic surface of the record media. Significant engineering time and experimentation ultimately solved the problem.

The initial solution was to use pressurized rotating media with high-altitude specifications. This solution functions at up to approximately 16,000 feet above mean sea level, but is not fully reliable. The drives also have slower transfer rates, so more drives were needed in the aircraft for efficient capture. There are other limitations of the rotating technology that are not desirable for a long-term solution, but the capture was accomplished. Engineers are currently testing a more promising technology for high-altitude capture using high-speed, solid-state drive technology. Early examples of this technology proved to be too slow for efficient capture, but new versions of the equipment are showing more promise.

There were concerns that a CITRIX deployment of the imagery and viewing software could have speed problems. Additionally, the Marine Corps is moving to ArcServer technology, so engineering time was devoted to alternative solutions. Engineers developed thin-client viewing software that could be used if needed.

Something New: An Oblique Mosaic

During the course of the contract, a feasibility question was raised: Was it possible to merge individual oblique images to create a base-wide oblique image? This idea was prompted by the loss, during a building fire, of a large traditional aerial photograph. Engineers developed a technique to tile and seamlessly merge multiple oblique photographs to form what looks like a single high-altitude — yet high-resolution — oblique image. This was especially challenging since oblique images don’t edge-match easily; each image has a different perspective, with each pixel being a different size and not rectangular in shape. Those challenges were overcome, and a single base-wide oblique image was created to replace the destroyed aerial photograph. Since the large mosaic was created from many low-altitude, high-resolution obliques, the final large oblique image had very fine resolution throughout.

3D Models

One of the deliverables requested under this contract was an interactive 3D model of a high-visibility location in the Washington D.C. area. The location presents security and logistics challenges, so an interactive 3D model will be very useful. The “wire frame” model was created from multiple oblique images by Precision Light Works (PLW) with a semi-automated process similar to stereo pair analysis.

Once the wire frame is created, the same imagery is automatically draped on the 3D model to create not only a photo-realistic model, but a photo-accurate model — meaning that features are accurately located on the models. The 3D model created by PLW can be used in various software viewers, including Google Earth. Some 3D viewers can also do measurements within the 3D model.

Public Works Report

PBS&J worked with Pictometry engineers to develop an implementation plan using oblique imagery for public works applications. One public works application surfaced because there was a need to conduct a survey of runway approaches to determine whether trees had grown into the glide paths or if unauthorized construction had occurred within the glide paths.

The traditional method to accomplish this task was with survey crews sighting and measuring objects on site — a time-consuming task. The ability to measure heights of vertical features made oblique imagery a natural choice for this application. PBS&J tested the concept and demonstrated the feasibility of doing surveys with the imagery, but more work will be needed to test the accuracy of this method and ultimately receive certification.

Fire Protection and Emergency Response Report

Another use of oblique imagery, which received significant publicity, is its use as a planning tool for firefighters en route to a fire. The imagery permits the firefighters to get the lay of the land, measure distances to fire hydrants, and view accessibility.
Many counties using the oblique imagery have statistically measured a reduction in fire attack time of 60 to 90 seconds.

This is a significant improvement, and the Marine Corps wanted to provide this advantage to their firefighters. The contract called for a firefighting implementation plan, and we had veteran Battalion Fire Chief Wayne Harper on our team to develop one. Paper reports have always left me cold, so I asked Harper, Why not deliver a functioning laptop, similar to those used by other firefighters, as a deliverable with the plan? We did exactly that, and delivered a fully functional Toughbook laptop configured with oblique imagery, GIS data, and software that could be used in fire trucks for tactical planning. This hands-on working example went further than just a paper report, and should facilitate the installation of similar capabilities on all USMC fire trucks.

Taking the Lead

Usually the Marine Corps is at the “tip of the spear” in world conflicts and combat situations, but rarely are they in the lead when it comes to technology. With this oblique imagery project, the USMC has certainly moved to the forefront with oblique imagery technology.

Although not part of the Marine Corps contract, the development work done to complete the contract underpinned potential war fighter applications. The research and testing clearly points the way to make this technology available to deployed combat units in-theater in an operational mode that could provide near-real-time imagery to ground troops. To this end, Pictometry recently signed an alliance partnership with a leading defense contractor to work on a number of related military projects.

Photos: Art Kalinski