There is little dispute that every land development project starts at roughly the same place – with a survey. Until the land is properly and accurately measured, little onsite activity can begin.

In some instances, the survey being used to define the property may be decades old. However, in many cases, a new survey must be completed.

An emerging development is the establishment of RTK GPS base stations. There are a number of reasons why this is happening, but most revolve around one of these four motivating factors:
1) Significant time savings – eliminates set-up time, which can often be lengthy

2) Helps eliminate errors due to a wide variety of variables that are often present

3) Provides a common geodetic system that standardizes the data that is collected in the area

And for Public Safety Grade Base Stations:
4) Built-in redundancies so that circumstantial variables will not impact the data collection and delivery process.

Reviewing GIS, GPS, and Current Technology
Ironically, one of the most important decisions to be made initially by a surveyor is where to begin. The starting point, often called the point of beginning, must be a location that is generally agreed upon – or widely acknowledged – to be accurately identified. This becomes the starting “control” point and the base or reference point for the remaining measurements.

For the past two decades or so of RTK GPS, this has required a surveyor to set up at least two instruments – a base station (to hold the point of beginning) and a rover that is used to collect the data from throughout the area being surveyed.

Also, similar to other products and services, there are various grade levels of surveying – much of which is directly related to the accuracy of the survey data.

For instance, most GIS systems do not require pinpoint information. Typically sub-meter accuracy is “good enough” since it is rather easy to locate a house either on the computer or on the street if you are within three feet! The same situation exists with most consumer GPS products. Survey-grade data describes the accuracy required for surveying boundaries and property lines, and legal surveys, usually require accuracy of about a half-inch.

Due to the equipment, processes, and expertise needed in order to obtain survey-grade data, there is a corresponding escalation in costs for collecting and processing this high quality data.

For these RTK systems, virtually all communication between today’s base and rover units utilizes cellular or short-range UHF technology. This inherently creates a couple of limitations:

1) UHF signals are often plagued by interference and typically have a maximum range of approximately 7 miles even under ideal conditions.

2) Cellular communication can be even more problematic – as clearly illustrated by 9/11 and hurricane Katrina. Not only is cellular coverage sparse in many areas, but since surveying data is sent in a digital format (a low priority for cellular companies), when cellular use is high, digital data users are dropped.

Due to these shortcomings, plus the many other new benefits, a new application of the technology is emerging. It is the use of permanent base stations with better and more reliable communication technology. “Public Safety Grade” RTK Base Station systems are now being utilized to ensure the optimal reliability and dependability.

“Two areas need to be addressed to ensure that public safety needs can be met when a situation arises,” explains Eagle Point’s Lance Andre, the company’s SMI Surveying Product Manager. “They are the physical equipment characteristics and
the communication mechanism. Hurricane Katrina clearly illustrated both of these. It is of great concern to public safety and homeland security officials that GIS, GPS, and surveying data be available, ready, and accurate when they are needed.”

Andre related that cell phones were virtually useless following the hurricane because cellular technology was simply overwhelmed or unavailable in critical areas. The military and army corps was forced to utilize satellite phones and private VHF bands to effectively communicate with the region.

Additionally, to withstand an extreme weather event (hurricane or tornado) the physical equipment must be sturdy and rugged enough to survive.

In public safety-grade reference stations, neither UHF nor cellular technology should be used as the primary method for distribution of GPS corrections.

“Eagle Point’s Public Safety-Grade solutions add multiple levels of redundancy for each component of the RTK infrastructure. For example, we employ two or more redundant communication systems which could include: Satellite, VHF, UHF, SHF, Cellular IP and WiFi to name the more common ones. Each of these systems has its advantages/disadvantages, so a properly designed system must leverage these attributes in such a way to deliver the required reliability. Because of our consultative approach in custom designing these base stations we can work the client and other agencies like the FCC in deploying the best possible solution.

Benefits of Using Public Safety-Grade Base Stations
As stated earlier, the establishment of a starting point and setting up a base location to begin the surveying process is essential, and often time-consuming – not only in actually setting up equipment, but also the research time spent by the surveyor to determine the integrity of the available data and best starting point at which to begin.

1. Time Savings
Not surprisingly, organizations that spend a large amount of time surveying in a particular area can achieve a significant time-savings through the permanent establishment of a base station. Leading the way are state departments of transportation. They are even taking the concept a step further by creating base station networks. These networks allow for a dramatic reduction in the total number of abase stations required to cover large geographical areas.

There are even some private organizations that are proactively establishing base stations for certain areas and then authorizing others to tap into and utilize the system and data (see sidebar).

2. Helps Eliminate Errors
By eliminating the time consuming step of entering starting information and setting up the equipment, the user of a permanent base station has eliminated the possibility for errors in base setup, equipment errors, coordinate entry and location determination, etc. Also, numerous other errors can occur with mobile equipment such as multipath, settling of the equipment as temperature changes during the day, poor power supply, etc.

3. Common Geodetic System
There are a number of standards for surveying data – and too technical to explain in this article. However, consider the various CAD packages and or building designs that every designer and contractor uses. All have a “system,” but not all “play well” with others.

By utilizing a common base station that is set on one standard, organizations can be assured of the fact that anybody using their correction data will be utilizing the same standards when new information is submitted. For instance, if a DOT is having an outside engineering firm or surveying firm submit data, and the DOT permits the use of its base station, it knows that the information it receives from its service providers will be provided in a common geodetic reference system compatible with its internal system – thus avoiding any translation or data conversion.

4. Reliability and Dependability
Reliability is perhaps the most important component of a public safety-grade system.

“Mobile systems are not reliable enough to be considered public safety grade for a number of reasons:

1) They don’t and can’t operate 24/7/365

2) because they are “mobile” they lack redundancy in nearly all areas to save weight

3) Each time a mobile unit is setup it will be slightly different in its location and varing multipath environments add to its lack of dependability

4) these systems are easily stolen (this item along has been justification for many cities to setup a permanent base station)

Beneficiaries of Public Safety-Grade Base Stations
With the establishment of top level base stations and networks, there can be a significant expansion of the use of quality GPS technology.

As indicated, emergency management, GIS, and surveying professionals – and their clients - can be immediate benefactors because it will save time and money while increasing accuracy. However, there are a number of ancillary users who could utilize the technology as well.

Among them are:
• Municipal Governments
• Navigation (Vehicles)
• Machine Control & Guidance (Construction & Agricultural)
• Autonomous Vehicles
• Photogrammetry
• Forensic Science

The cost of establishing a permanent base station can vary greatly. Depending upon the stability and redundancies requested a system could be set up for a reasonable $8,000 investment. A public safety-grade set-up can run up to $50,000.

Andre, however, does point out one major concern he has with this emerging trend.

“This technology is new enough that uneducated vendors are misleading potential buyers. By not properly informing them of the many weaknesses of each component of the system and by not recommending the best solution for them,” warns Andre. “Some software that comes with the hardware is very proprietary and will not work with other units or networks. I encourage anyone moving into this technology to investigate thoroughly and ask as many questions as they can about the reliability of each part of the system and the limitations and compatibility with existing systems already in use by the proposed beneficiaries.”  SLDT