From the Ground Up
May 1, 2006
Today's high-end digital cameras were first introduced to the mapping community in 2002. They have provided impressive gains in the quality of imagery over film and are altering the way many mapping projects are produced. Moreover, they provide capabilities that are not possible with their film counterparts such as the ability to capture black and white, true color and color infrared imagery in a single flyover of a project site.
Implementation of these digital cameras in mapping firms around the world was slow at first, but the last year has seen an explosion in the acquisition and use of the cameras for mapping projects. For example, worldwide sales of Leica Geosystems' (Norcross, Ga.) ADS40 digital sensor in 2005 increased some 250 percent over sales of the same sensor in 2002.
If the cameras provide such an increase in capabilities, why were mapping firms slow to implement them at first? Cost is certainly a factor, since these new systems typically require an investment of more than $1 million. After the initial camera purchase, most firms also need to upgrade their office computing technology to handle the vast amounts of digital data that is captured with these systems. A full day's flight mission can require almost 1 terabyte of data storage.
Also, the flight crew has to possess new skills that weren't necessarily required with film acquisition. In addition to their knowledge of photography, weather systems and GPS navigation, crews working with digital sensors must also have strong computer skills. The crew must be efficient in downloading and backing up vast amounts of digital imagery data, viewing digital image clips to ensure quality was upheld and cloud-free conditions were met during the mission, and troubleshooting the computer systems and multiple data cables that provide the brains for these cameras. The workday for a digital crew normally extends well beyond the completion of the flyover.
Digital Mapping TechnologyProviders of new digital camera technology have taken different paths in the design of their sensors. The Intergraph (Madison, Ala.) Digital Mapping Camera (DMC) and Vexcel (Boulder, Colo.) UltraCam-D are frame-based sensors, meaning they operate much like the digital camera you may have at home or in your office. They take one rectangular frame of photography at a time. The Leica ADS40 and new Jena-Optronik (Jena, Germany) JAS 150, however, have a totally different design approach and are known as pushbroom sensors. They capture imagery by rows, one row of pixels at a time. These rows are then combined to form a long image that follows along the entire flight path of the airplane.
Each of these technologies has its advantages and disadvantages in mapping applications. Choosing the correct technology, therefore, depends on the individual project requirements. What type of mapping information is to be developed in the downstream production workflow? What accuracy and pixel resolution is required for the project deliverables? What software platforms will the client use for the provided information? The answers to these questions are important in selecting the correct digital approach for a project.
Providing More InformationThe information contained in first-generation digital images is impressive. Digital mapping cameras typically provide 12 bits of digital information as compared to 8 bits of information gained from a scanned film image. At first this may sound like an insignificant gain. Consider, however, that a scanned black and white image will be digitally rendered as 256 shades of gray ranging from 0 (black) to 255 (white). The same image captured with a precision 12-bit digital camera will have a total of 4,096 shades of gray. The 12-bit image holds 16 times more information than the 8-bit image and that change is anything but insignificant! The same argument holds true for the individual red, green and blue bands that make up a color image. Each band has 16 times the radiometric information as found in the traditionally scanned film image.
This increase in information in the 12-bit imagery can result in an increase in flying hours per day and days per year as clients become comfortable with the capabilities of these still-new digital cameras. This increase is a result of the ability to fly at lower sun angles or conduct flights on what would be considered a marginal weather day for film acquisition. The digital imagery acquired under these reduced conditions will still be better than most film imagery acquired under near-perfect conditions. And that is very important to both the mapping professionals using this acquisition technology and their clients who will be working with the imagery.
Another major benefit to this high-end digital camera technology is the ability to acquire color, black and white, and infrared information in a single pass. In the film world, this requires three passes of the aircraft over the project area with three different film types. The additional photo acquisition can be significant in terms of cost, but the downstream office production can be even more significant because each of the photo exposures will be acquired at slightly different locations during the photo flights; therefore, each film type has to be controlled independently of the others. In the digital world, the color, black and white and infrared images have exactly the same positional and rotational parameters since they were taken simultaneously. This alone can greatly reduce the final project costs for the client. As a result, many clients are now requesting color infrared imagery in addition to their base mapping deliverable of color or black and white; this is driving a number of new applications, particularly in the environmental arena.
Finally, no discussion of first-generation digital imagery is complete without a mention of the image quality of true digital versus film. Scanned digital imagery is always affected by "noise" that occurs in the processing, handling and scanning of film. It is very easy to add scratches, dust, lint and hairs to any image scan, even when extreme care is used when handling the film. Also, very high-resolution scans can become grainy because of the composition of the image on film. And these artifacts are readily visible in the digital product when they occur.
Time-critical ProductionAnother advantage of digital mapping cameras has to do with the timing of mapping production. The downstream map production can begin immediately upon landing. In the film world, the film has to first be processed in a photo lab, then scanned to convert it into the digital world. For a typical project, this process normally requires a couple of weeks, but could be shortened to a couple of days for an emergency project. But in times of an emergency created by a national disaster or security threat, a few days may be the difference between an effective solution and useless information.
Also, the camera operator has the ability to review the imagery in-air before leaving a project site. This can be important, particularly for projects that are further away from a firm's home base, or again for projects that are time-critical. This is not possible with film.
ArchivingOne of the issues that must be dealt with in the digital world is the temporary storage and archiving of the imagery. This is very simple in the film world as a roll of film takes up a relatively small amount of space and is easily stored at very little cost. The film can easily be stored on a shelf until the imagery is required for the mapping production. As for archiving, in an environmentally controlled storage space, film can last for decades.
Archiving of the raw imagery becomes more challenging with a true digital collect, although technology has improved considerably since the first large-format digital cameras were introduced. Today, many firms use external hard drives or DVDs to backup the raw digital imagery. Some clients choose to archive all of the raw image data at their facilities so they can easily access the information down the road.
This may sound trivial, but remember that a single mapping project can include several terabytes of raw imagery. And to make this technology profitable, a mapping firm needs to keep the sensor in the air most of the year. The volume of data from a single year can be surprising.
Growth and DemandWhy is digital camera technology experiencing explosive growth in the mapping arena right now? Because digital cameras provide the highest quality imagery available today. The imagery is crisp, rich in information and generally free from the artifacts of dust, lint or scratches that are common in scanned film. More information can be acquired in a single pass of the aircraft and more clients are finding uses for a combination of the black and white, true color and color infrared images made possible by this technology.
Also, now that several years have passed since the introduction of these high-end systems, the sensors have improved and become more reliable. Most of the nagging problems of the early sensor models have been addressed and reliability is critical to firms
flying these sensors. But one of the biggest reasons that so many new systems are being adopted is that clients are now demanding them for their projects. With the right research and study, a willingness to take on today's newer, more efficient technology and a vision for tomorrow, a mapping firm can reap the benefits from digital cameras.