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From the Ground Up

February 28, 2006
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Surveying and mapping professionals have worked closely together in the production of topographic and planimetric maps over time. However, tremendous changes in technology over the last several years have affected the balance between the surveying effort and the mapping effort, lessening the amount of ground control and the manpower effort on the ground required for the typical project.

GPS has played a large role in the changes in both the ground effort and the aerial acquisition. What once required weeks of conventional control traverses and differential level runs to establish ground control for a typical project can now be accomplished in a couple of days with static GPS surveys. Moreover, airborne GPS (ABGPS) photo acquisition, where accurate GPS positions for the camera are established during flight at each photo exposure, has significantly decreased the number of control points required on large projects. For example, a recent countywide mapping project was completed with 14 ground control points (GCPs) using ABGPS photo acquisition. The same project would have required 74 GCPs under a conventional photo acquisition approach to achieve the same mapping accuracies.

While many of the changes in the mapping profession have resulted in a lessened need for surveying support, other changes have created new opportunities for the surveying professional. Understanding the climate of the mapping arena can allow surveyors to capitalize on these opportunities.



Surveying professionals provide invaluable services to the mapping profession, including geodetic control surveying, accuracy assessment and ground support during aerial acquisition.

Need for Services

Many mapping firms have geodetic surveyors on their staff. But most firms also employ a number of surveying subconsultants during the year to help them meet their project requirements. As a mapping professional, having reliable subconsultants is important for two primary reasons.

First, the geographical area that most mapping firms cover is very large because of the nature of the mapping business. The number of mapping firms in the United States is relatively small and a large radius can be covered thanks to the range of the typical aircraft used in acquisition. Ground surveying and aerial acquisition are typically the only location-critical parts to a mapping project as other project related mapping work is carried out in the mapping office, which may be hundreds or thousands of miles from the project site. And it only makes sense that the distance from the mapping office to the project site often makes it advantageous for the mapping firm to use the services of a local surveyor in lieu of its own personnel to avoid travel-related costs.

Secondly, the need for surveying support in a mapping firm can be highly cyclical as the peak season for surveying typically coincides with the time when leaves are off deciduous trees, which means late fall to early spring. Therefore, if a mapping firm has surveyors on staff, they are likely to have a smaller number than needed for the peak times to avoid being overstaffed in that area at other times of the year.

Surveyors have been providing professional services to mapping firms for decades in the way of targeting and establishing positional values of ground control points. But as mentioned earlier, this is an area where both GPS and ABGPS have provided a significant reduction in the amount of surveying work required on a typical project. ABGPS techniques require, however, one or more ground-based GPS receivers set up over known control points during the entire flight window. The GPS data collected at these points are subsequently used in the post-processing of the flight data. Similarly, aerial LiDAR data acquisition relies on ABGPS techniques to position the LiDAR sensor during flight, and therefore the same requirement for ground-based GPS acquisition during flight exists.

Accuracy assessment is another important area that provides opportunity for professional services to a mapping firm. Many clients require formal accuracy assessments as a project deliverable, whether the project involves traditional mapping or LiDAR collection. For example, the FEMA guidelines for LiDAR projects require a separate Digital Elevation Model (DEM) assessment for each of the seven ground cover types (e.g., bare-earth and low grass; high grass, weeds and crops; brush lands and low trees; and urban areas) found in a project area. Many times RTK observations can be used to quickly establish the positional values of the checkpoints used in these accuracy assessments.

Finally, for some projects it is necessary for a mapping firm to pair up with a surveying firm to provide non-mapping related information such as a boundary or easement survey, or to provide information that cannot be seen in the photography such as smaller features like fire hydrants or manholes, or underground utility line locations.



Setting Yourself Apart

There are many things you can do to set yourself apart as a surveyor to increase your value to mapping professionals. First, understand that weather is the biggest challenge for any mapping firm. Normally acquisition is a race against time and Mother Nature. Because the number of good weather days in a project area are limited, mapping firms must be willing to fly at any time, and that includes weekends and holidays. A lost flying day for a mapping firm results in a substantial loss of revenue. Understand that your support in manning ground-based GPS stations during the aerial acquisition may be required on a 24/7 basis. When providing ground support during an ABGPS photography mission, the flexibility and willingness to provide services when the weather cooperates is often crucial to the project's success.

LiDAR collection can provide an additional complication in terms of ground support. Because LiDAR is an active sensor (it sends out its own energy), it does not have the restriction of being flown only during the daylight hours as found with aerial photography. In fact, many times it is much better to fly these sensors at night when weather is typically calmer and when potential complications with other air traffic are at a minimum (particularly in urban areas around major airports). Therefore, it may become necessary to have employees available for night work.

In terms of technology, it should be apparent that GPS is a requirement for mapping support these days. The ability to collect, download and archive relatively large volumes of raw GPS data at either 1.0 or 0.5-second epochs is usually necessary for airborne support. And having personnel who are comfortable with differential, static and RTK GPS techniques for varying project requirements builds value.

Effective communication is also critical. It is important to have a good line of communication with the photogrammetrist, asking questions like, "When do targets need to be placed?" "What configuration should be used in targeting and where should the actual control point be located within the target?" There are several different options here and most firms have their own preferences. Other questions to ask include: "Do the targets need to be "˜maintained' during the flying season?" "When can targets be removed?" "What surveying methods are appropriate to meet the accuracy requirements of the project?" "What datum and coordinate projection should be used and what digital format works best in providing information?"

Moreover, it is critically important to be very careful when communicating with the public during any onsite work. Being politically correct in this communication is paramount. Remember that in many cases, mapping is being conducted for some type of new development or construction-a roadway, a new residential development or possibly an addition to a utility line. In any of these cases, it is likely that some of the residents in the area will be opposed to the new development and concerned when they see fieldwork or targeting taking place near them. Being a good ambassador can be very important to the ultimate mapping client, which in this scenario would be the developer or contractor. Therefore, it is very important to gain an understanding from the mapping professional of what can and what cannot be disclosed to the general public. A communication plan understood by all field staff can be critically important to the overall success of the project.



Forming An Effective Partnership

Do you want to grow your business by increasing the services you provide to mapping professionals? If so, first look inward. Do you have a full complement of GPS hardware and the knowledge to use it in varying applications? Do you have the flexibility to provide ground support of flight operations when the weather cooperates, even if this occurs on a weekend or holiday?

If so, look outward for mapping firms that may provide services in your area. Provide them with details on your GPS hardware, collection capabilities and the knowledge of your key staff. Define the geographical area where you are interested in providing professional services. For smaller projects, that area is likely to be within a few hundred miles of your office due to cost efficiencies. But that area will typically increase as projects become larger. Inform them of the states where you have licensed professionals. This is very important to mapping projects today.

Have them provide you with details of their preferences for target construction, location and digital file requirements. And be sure to understand individual project considerations, such as the accuracy requirements for new control points established and a communication plan for dealing with the public. An effective partnership between surveying and mapping professionals can be a rewarding effort for both parties.

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