Technology Tools Cut Time, Boost Accuracy of Geodetic Surveying Projects
In recent years, technology has become crucial for streamlining geodetic surveying to make it quicker, easier, and as accurate as possible. For decades, a theodolite was the main tool used to build graphical maps of terrain derived from distances and vertical and horizontal angles. Today, global positioning technology is the chief tool to accomplish this task. Surveyors have started to rely heavily on GNSS solutions to improve field work and to ensure the accuracy of numerous control networks for measured points on the Earth’s surface.
As the instruments used in geodetic surveying have advanced, software has emerged to make better use of the data. Modern tools allow surveyors to store and edit the geodetic position of grid points, identify and label geodetic positions within a drawing, transform between ellipsoidal and orthometric elevations using geoid files, and detect an appropriate coordinate system based on a latitude and longitude. With the right software, surveyors are saving time and improving the accuracy of their work.
Numerous software programs exist for geodetic surveying that can accomplish day-to-day routine processing, coordination and adjustment of spatial survey data and handle complex networks of geodetic coordinates.
Coordinates Transformation Performed More Easily, Quickly
The N.E. Parrott Surveys Limited surveying firm in Happy Valley—Goose Bay, Newfoundland, uses geodetic surveying routinely. “We’re dealing with geodetic coordinates every day,” said Roger Slaney, a surveyor with N.E. Parrott for 26 years. “If we’re doing land surveys, topographic surveys, we use geodetic surveying techniques. If we’re dealing with construction, we might have just a flat plane, such as roads that have a 300 kilometers length, so you have to take into account all the effects of the shape of the earth.”
More specifically, Slaney uses this survey method to get coordinates for surveying legal land parcels, topo surveys, and road construction, mining and railroad projects. His firm employs a combination of tools including theodolites, total stations, RTK satellite navigation systems, and laser scanners. Also included in Slaney’s toolbox is the MicroSurvey CAD software program, which he has been using since 2000.
Slaney has performed a lot of geodetic survey work for iron ore mining projects in northern Labrador along the border between this area and Quebec, where surveys are required to establish the holes for drilling, or to establish the boundary of leases. Trestles for the boundaries of the mining lot are rectangular in shape, yet are issued by the Canadian government in a UTM NAD 27 coordinate. “When we’re surveying up there with our GPS, we’re surveying in UTM NAD 83 coordinates,” Slaney said. “So, we’d have to convert from NAD 27 to NAD 83.”
There are considerable differences in both the latitude and longitude coordinates and the northing and easting values. Also, these shifts vary considerably with location, and there is no consistent shift which can be applied for all areas. “You want to keep the scale factor down because there’s a bigger scale factor between UTM and MTM,” Slaney said.
The MicroSurvey CAD program proves invaluable on Slaney’s surveying projects. “With MicroSurveyCAD, if you’re working in real-world units, you can take a magnetic survey once you’ve established one of the legs of that traverse, and the software automatically will rotate and scale that traverse into your data,” said Slaney.
If calculations and transforming of coordinates between two zones had to be done with older methods, it would be a long, tedious process requiring the use of many formulas. “When I perform a coordinate transformation with MicroSurveyCAD, I can use it to pick up a couple of coordinates at random and check them to see if their results are accurate,” said Slaney. “Now, we’re doing these coordinate transformations every day with MicroSurveyCAD.”
Another good example of the software’s value with geodetic surveying is a railroad survey project that Slaney handled where fluctuating coordinates was at issue. Slaney performed a survey for a railroad that is 300 kilometers west of where a mine is located. It was necessary to mine ore from a pit and get it to the location of the rail line. “But you’ve got a different zone of coordinates in between the mine and the railway,” said Slaney. “We had to be able to calculate the coordinates and then to convert them between different systems.” MicroSurveyCAD was able to handle this conversion easily. “If you had to calculate all of these coordinate changes manually, it would be very tedious,” said Slaney. “It (the software) also eliminates user error. And I get results almost instantly.”
Least Squares Adjustments Proves Helpful for Geodetic Surveys
For John Ranum, survey project coordinator for the Washington County Public Works Survey and Land Management Division, Twin Cities, Minn., geodetic surveying is only about 20 percent of survey projects handled. “But it’s really the foundation for everything else we do,” said Ranum. Working for the county is different from working for a private surveying company. One advantage with doing county survey work that Ranum cites is that he is always working with the same datum and coordinate system. “We’re familiar with the control we have, and we don’t have to perform coordinate transformations,” said Ranum. Still, one challenge remains: Geodetic network control adjustments don’t always fit. Points in the field and points on paper are rarely the same. There’s a reason they’re called adjustments; the solution is never perfect. “We strive to create geodetic control networks that are an accurate representation of the points on the ground,” said Ranum. “Occasionally, a network adjustment doesn’t result in the level of precision we expected. Has a point or points been disturbed? Was there an error in the field? Was the equipment configured correctly? Are my expectations realistic?” the surveyor poses. The biggest challenge Ranum faces is creating a network adjustment that is a true representation of the reality on the ground, and creating networks that are the best possible fit and can be used with confidence through each phase of a project. Added Ranum: “Our control is used to collect data necessary to determine boundaries, construct roadways, and set boundary markers; it has to be reliable.”
To conquer these issues, and to accomplish geodetic surveying overall, Ranum has been using the MicroSurvey STAR*NET least squares adjustment program along with Trimble Business Center to edit, process and adjust survey data that is imported straight from the field. STAR*NET proves particularly helpful because it is a mathematically correct method for checking the results of surveys of any size, especially traverses, and is ideal for combining conventional, GPS, and leveling data into a control network and for checking the validity of results.
A typical example of how Ranum uses STAR*NET is when he does conventional surveying. One project involved platting a highway right-of-way in a nearby township in Washington County. The existing right-of-way wasn’t wide enough for county construction requirements. Therefore, the county had to purchase additional property for the highway right-of-way. To determine the width of this right-of-way, all property evidence, such as fences, retaining walls, property irons, etc., had to be located. But areas like this one are also tree covered, which means GNSS surveying can’t be used to establish all of the control needed. Still, “as is often the case, we needed to run several traverses to extend that control and densify the control network,” said Ranum. Conventional traversing is still an integral part of geodetic surveying. “The beauty about STAR*NET lease squares adjustment is that it utilizes redundant measurements throughout a traverse as well as data captured from numerous traverses,” said Ranum. “This strengthens the adjustment and helps identify its weaknesses.” Ranum believes STAR*NET has refined the reporting of how well an adjustment has met a surveyor’s expectations based on user-determined settings and the field data. Residual errors that are significantly higher than the determined standard errors are flagged for easy identification. Error ellipses are also reported, helping identify local errors as well as structural weaknesses in the network design. Once errors or areas of weakness are identified, the input data can be easily edited, Ranum observed.
Ranum also noted that there is a lot of flexibility with types of measurements: 2D, 3D, angle only, horizontal distance, slope distance, etc. Again, these can be easily edited within the data file. A single angle/distance measurement with a bad distance, for instance, can be changed to an angle only measurement.
“Often an adjustment will suggest your measurements are as accurate and precise as expected, but the control is not,” said Ranum. “Each component of any control station may be held fixed, partially fixed, or free. Most adjustments are fairly simple with STAR*NET, but if needed, there is a great deal of detail that can be analyzed and changes made to your data and the adjustment settings.”
The traverses and survey data are exported Trimble TSC3 recorder, then converted by a MicroSurvey CAD data converter into a format that’s required by STAR*NET. Once the adjusted data is brought into MicroSurvey CAD, the AutoMap utility kicks in to provide automated drafting from point description codes. “These coded entries become much more readable with full descriptions,” said Ranum. “So, we might have a code such as CIM, drop that into MicroSurveyCAD, and then AutoMap will automatically give that the correct symbol and the full, correct description and put it on the desired layer (of the survey map) with the desired color. That’s very useful.” This process also saves time because it means Ranum doesn’t have to enter lengthy descriptions. Ranum added: “If you have a client who wants this all done differently---for instance, a different type of description or format--- you can update your AutoMap to accommodate this without changing your description codes used in the field.”
Big Time Savings Before and During Surveys
Time is money, as the old saying goes, and this applies most pointedly in the surveying profession. Slaney, the Newfoundland surveyor, says MicroSurvey CAD cuts down on time for preparation to go into the field to tackle a surveying project. This is a significant advantage given that many of the locales for Slaney’s work are remote, requiring that he and his survey crew must fly into them. “If we have to fly to a remote location, we want our guys to be as equipped as they can be before they get there,” Slaney said. “In a lot of cases, we have the job done theoretically before it’s done physically.” For instance, if a client wants Slaney’s firm to lay out a monument block in a survey plat, this can be accomplished before a crew sets foot on the ground using MicroSurvey CAD. “From there, we would establish the control by laying it out, using the software to do our preliminary work, calculations and coordinates,” Slaney said.
Without the aid of today’s technology tools, geodetic surveying would require enormous blocks of time to accomplish transformation of coordinates between two zones, or coordinate conversions. Software such as MicroSurvey CAD greatly streamlines this process, offers huge time savings, and assures the surveyor that calculations are accurate. The software is ideal for viewing combined scale factors and convergence angles at any point in the surveyor’s drawing or project database.
In addition, the availability of GNSS technology is extremely valuable for measuring the relationships between points on the Earth’s surface and obtaining gravity differences between these points. It also can accomplish this in a greatly reduced amount of time compared to older surveying methods. To provide an even greater assurance and redundancy, a least squares adjustment program like STAR*NET can reference the parts of a data set that do not fit the rest of the data collected, allowing surveyors to easily detect blunders. This can mean huge time and labor savings, plus make workflow much quicker and smoother.