Scanning the Mapping Toolbox

October 1, 2004
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Today's mapping technology provides photogrammetrists and land surveyors many opportunities.

In August, for the first time in its 86-year history, the PGA used an aerial image for the official illustration of its championship host golf course. On May 17th, AERO-METRIC Inc., of Sheboygan, Wisconsin, captured the image of Whistling Straits Golf Course with its digital mapping camera. AERO-METRIC's Digital Design Team added all the detail, including cars and tents, to yield an image that looked like it did during the actual event.


Two particular developments in today's mapping technology have changed how data is collected and developed: LiDAR and digital cameras. The effect of these developments on the surveyor and mapper hinges on whether these professionals embrace the technology. Let's scan the mapping toolbox containing these technologies, and review some of the success stories of mapping firms using them.

LiDAR (Light Detection And Ranging)

Methodology and Advantages

Having come a long way in a decade, LiDAR is now considered a more than acceptable method of data collection for mapping purposes. It is estimated that more than 40 planes in the United States fly projects using LiDAR and digital technology.

The amount of data collected with LiDAR is staggering-from 50,000 to 100,000 points per second (depending on the hardware), each having X,Y,Z attributes. The complete processing of terrain elevation data used to take weeks or months with a stereoplotter; now it takes mere days with a LiDAR unit. Further, this production rate allows clients to receive data at a fraction of the cost of conventional mapping methods. Another benefit of LiDAR is that the larger the area to be mapped, the lower the cost per acre is. Many of the final product deliverables produced are based on the often-preferred two-foot vertical standard established by FEMA (Federal Emergency Mapping Agency). Most deliverables are digital elevation models with the option of contours or other data sets.

Flying the unit, as it is called, and processing the data are challenging parts of producing good, usable LiDAR data. Today, an estimated one-half of LiDAR jobs are flown at night. The reasons for this are that weather conditions are often more favorable and that LiDAR is not restricted to the daylight hours like conventional photography since it is an "active" sensor that uses its own energy-the LiDAR laser pulse illuminates the ground. Nighttime also offers little commercial air traffic, so flight lines are uninterrupted.

It is probable that in the near future LiDAR data will be available covering very large geographic areas, in some cases whole states. The surveyor will be able to contract with the owners of this data to extract particular areas of data and to provide the finished products for surveying and engineering projects at a cost that will allow the original owner of the data and the land surveyor to both make a profit. This will depend on the individual business acumen of the land surveyor.

The Optech ALTM 3100
Equipment Options

Equipment options in the area of the growing LiDAR technology products include the Optech ALTM 3070 and the new Optech ALTM 3100 (Optech Inc., Toronto, Ontario, Canada), and the Leica ALS40 and ALS50 Airborne Laser Scanners (Leica Geosystems, Atlanta, Ga.).

Major LiDAR manufacturer Optech introduced its first 2 kHz unit in 1993. This year, Optech introduced a model with the highest pulse rate on the market-its 100 kHz unit. The ALTM 3100 offers area coverage rates as high as 100 kHz at 1,100 m altitude. Additionally, the system can fly as high as 3,500 m with coverage rates as high as 33 kHz.

From the first LiDAR unit made available in 1998, soon known in the market as the Leica ALS40 Airborne Laser Scanner, which collected elevation points at a rate of 1,000 per second, Leica Geosystems has had a pulse on LiDAR technology since its birth. Today, the redesigned ALS40, known as the ALS50, collects elevation data at a rate up to 83,000 points per second.

The Intergraph Z/I Imaging DMC

Digital Aerial Cameras

Just as the digital camera has all but replaced the pocket film camera, the benefits of the digital world in mapping technology are proving advantageous over the traditional film capture. Digital aerial cameras are on the technology curve today where LiDAR was about five years ago. For many firms, it is still quite early for implementing this technology. While costs are beginning to level off, it is expected to be a few more years before the technology is affordable for most interested firms.

Some of the larger mapping firms, however, are utilizing this digital technology to its ability and with great success today. But the decision of which camera to purchase isn't an easy one. Since the purchase of a digital camera is extremely expensive-about $800,000 to $1.8 million-it is not surprising that firms very seriously take into account many important factors. Resolution, the higher the better, may be the most important factor of them all. The reputation of the maker is taken into account just as it is for any other piece of equipment used on a regular basis. Customer service and support, and maintainence, repair and supply of parts weigh heavily in the decision. And, of course, cost holds an important place, just as it does for any purchase. Various methodologies for data collection are assessed as well.

The Vexcel UltraCam-D
In the digital market, Z/I Imaging, a division of Intergraph Mapping and Geospatial Solutions of Madison, Ala., and Vexcel Corporation of Boulder, Colo., have developed what is basically a very large version of the consumer digital camera. Z/I Imaging offers the DMC (Digital Mapping Camera) and Vexcel offers the UltraCam-D. The DMC, developed by Z/I Imaging and Carl Zeiss, a company known to provide surveyors with some of the most dependable and timeless surveying equipment in the past, is a more conventional camera with a lens for taking digital pictures. This camera fits into a standard aerial mapping camera mount and has eight digital camera heads. The middle four cameras collect black and white (panchromatic) overlapping images, which are then mosaicked into a single frame the size of an aerial film negative. During the mosaicking process, camera calibration parameters and platform calibrations are applied. Color or infrared images are created through a process called pan-sharpening. The color detail is collected with the remaining four camera heads: three of these are red, green and blue, and the fourth "color" is infrared.

The Leica ADS40
In contrast to Z/I Imaging and Vexcel's development strategy, Leica's ADS40 Airborne Digital Sensor uses what is known as a pushbroom sensor, which captures collections of thin strips of imagery as the plane flies along the flight line, then stitches them together to form one long strip of imagery that is as long as the flight line flown by the aircraft. The unit records a forward scan in black and white, and a rear scan in black and white. These two scans provide the stereo pair needed to develop mapping products. A third scan is directly under the aircraft and records the primary colors of RGB (red, green, blue) and can capture infrared as well. The imagery is captured in seamless strips with the width dependent on the height of the aircraft and the scale of the final product. The ADS40 images result in perfect RGB co-registration through special trichroid filters (filters that transmit light of three different colors when looked at from three different directions).

Each of these sensors has its advantages and disadvantages. Some choose the Leica cameras for producing digital orthophotos and the Z/I Imaging camera for more traditional mapping applications, but there is no norm for which cameras best perform particular jobs. Land surveyors often receive digital images from these cameras for use as a backdrop on a survey plat and other mapping jobs requested by clients.

One thing is for sure: film is on its way out from its legendary days of prominence. Digital cameras can capture black and white, true color and infrared imagery in a single pass, while film-based cameras require three passes to capture the same. Another distinct advantage of digital cameras over film is the overall radiometric quality of the imagery, which is far superior to film capture.

The New Mexico State Engineer's Office obtained this image of the Farmington, New Mexico area. The image was captured in panchromatic, color infrared, and color during a single flight with Intergraph's Z/I Imaging DMC system. 3001 Inc. captured this image for Bohannan Huston Inc. of Albuquerque, New Mexico.

Technology Success Stories

Technological advances are really only proven positive after execution is successful and clients are satisfied. A client of 3001 Inc. of New Orleans, La., a multi-disciplined spatial data company, was promised a very large digital ortho in infrared from another photogrammetric company for environmental research. About a week before the job was to be delivered, the client was told that the photography had not been flown. This client then called 3001, which flew and delivered the job about one week after the original due date. The client was not only happy to have the job completed, but said that the quality of the product supplied by 3001 far surpassed the client's original expectations. Another job came to 3001 from a state agency that had delayed ordering a mapping job for a highway extension. The client was more than satisfied when 3001 supplied digital data in the same week the project was flown.

Aero-Metric of Sheboygan, Wis., utilized its DMC on a newsworthy project this past August: the 2004 PGA Championship. Pat Olsen, the company's vice president, says that this orthophotography project "really spread the word that digital imaging from a digital sensor is here and has some great applications." Olsen says that at the time, there were only a few active DMCs in the United States. The team at Aero-Metric was able to use its DMC in an innovative way: they created a digital ortho image of the PGA Tournament site layout in Kohler, Wis. "We "˜created' all the facilities on the site, many of which were built and many of which were not," Olsen says. "We slipped [elements] into the orthophoto, including cars, tents, etc. The significant thing is, in the past, the PGA had always used artist's renderings. We went from renderings to this process. We skipped the scanner, went right from digital sensor to ortho." The images created by Aero-Metric were used in brochures, in the "˜You Are Here' signs throughout the site and on the daily pairing sheets indicating the location of the holes.

According to Darryl M. Gumm, project manager for the PGA job, the Aero-Metric team created about 200 separate layers and mosaicked 11 images to make the final project. Fine-tuning of the scale and various other elements took the job right up to the day before the event, but Aero-Metric delivered on its promise and the client, the PGA, was more than pleased.

Olsen says the PGA job is one of a dozen or so that have been completed using the digital sensor purchased last November and that about 15,000 exposures have been captured with it so far. Jobs have included orthophotography to a quarter of a foot pixel, two-foot contours and planimetric mapping at 1"=100' scale capture. According to Olsen, "[The DMC] allows us to generate high accuracy data for X,Y,Z, including work for surveyors and engineers."

At Ground Zero in New York following the World Trade Center attacks of September 11, 2001, EarthData of Frederick, Md., proved that digital technology and LiDAR can provide extremely valuable data in times of critical need. Two days after the attacks and for two months thereafter, a team from EarthData flew morning and evening flights using three sensors-LiDAR, thermal and digital imagery. Data was processed in nearby Albany in rapid turnaround-a mere eight hours-providing rapid response teams and government agencies with ortho imagery and 3D digital elevation models accurate to within 15 cm. With the resulting images, workers knew where ground objects were in their correct geographic positions, allowing them to obtain precise measurements between objects and to compute-accurately-the areas where they worked.

"You can, as a rapid response person, get pretty disillusioned out there that you're not making any progress," says Mary Hiatt, senior vice president-Corporate Marketing for EarthData Holdings Inc. of Frederick, Md. She says the images offered motivational help, showing the personnel involved that their hard work was indeed contributing to the progress of the search, rescue and recovery efforts. The imagery provided by EarthData also aided in observing shifts in the rubble pile and buildings in the vicinity, and in monitoring volumes at the landfill. "[Ground Zero] was the first time we used all three sensors," Hiatt says. "We had the nugget of insight for us to say "˜We really need to develop a much more robust, comprehensive rapid response system.' It was kind of the inspiration for what is now ARIES, which stands for Airborne Rapid Imaging for Emergency Support." Hiatt explains ARIES: "Very simply [ARIES] is a three-part system [including a] mobile command center (including high-tech communications, visualization software, plotters, etc.), everything needed for processing sensor airborne data, and a rapid downlink to download the data from the aircraft as it's flying in real-time to the mobile command center."

The system will utilize any of EarthData's four Leica ADS40 units along with LiDAR technology and the integration of technologies from other program partners. Since its work in New York, EarthData has received a $3 million grant from the Department of Homeland Security's Office of Domestic Preparedness to develop a prototype of ARIES and to perform a proof of concept of ARIES. The system is hoped to provide data at a three-hour turnaround from data acquisition to delivery-a great stride in mapping technology.

Image of the Grand Canyon produced by a Leica Geosystems ALS50 Airborne Laser Scanner.

A Promising Future

The advantages of today's mapping options are numerous: improved image quality over film alternatives, enhanced image content, extreme resolution and accuracy. Users also have the advantages of producing multiple image products, conducting jobs with rapid turnaround, and reducing cost and time over conventional methods. The recommendation for land surveyors is to educate themselves on these tools and incorporate their use efficiently and effectively.

With the rise in client knowledge, and thus, the rise in requirements for projects from this knowledge, it is important for land surveyors to keep a pulse on accuracy assessments and standards as well, such as the Federal Geographic Data Committee's National Standard for Spatial Data Accuracy (NSSDA, see www.fgdc.gov). Those land surveyors who keep up with standards will have an edge over those who do not by fulfilling the need for accurate ground assessments. Further, it is important for land surveyors to remain knowledgeable in mapping technologies as the two disciplines complement each other. "When a team of professionals understand and have a working understanding and appreciation of each other's disciplines, there's much more synergy in that team. So the benefit in the end is for the client," says EarthData's Hiatt.

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