For most surveying projects, speed, efficiency and accuracy of measurements are paramount. Since time truly is money in the surveying business, the goal is to reduce random error inherent in survey measurements. The best way to confidently accomplish this objective is through a least squares adjustment. It’s a versatile and helpful method. Least squares adjustment can be applied to something as simple as a resection or a more complicated situation such as a three-dimensional network. This method can accomplish several key steps: solve resections, adjust a network, adjust traverses, hunt down blunders in the data you’re observing, blend GPS vectors and total station work, and differential leveling data into one project. The desired result is to get adjusted coordinates that are more reliable and accurate compared to those obtained from simple intersection and traverse adjustments.
While not the only software program available to accomplish least squares adjustment, MicroSurvey STAR*NET has become one of the most popular and routinely used packages for this important method. Keep in mind that least squares adjustment is a processing tool in surveying, really. In other words, it’s a way to process all of your measurements simultaneously to achieve the best, most precise results. STAR*NET, which MicroSurvey acquired from Starplus Software in 2010 and has since offered through numerous upgraded and improved versions, is well adapted to help its users perform least squares adjustment with confidence. Striving to make the software even better, MicroSurvey has just unveiled version 8 along with a massively updated version 8.1. Different users will have different reasons to upgrade to this improved software package. But the new version seems to have something for everyone, suggests Brian Sloman, MicroSurvey’s Desktop Products Manager. “In fact, nearly all of the new features built into it came directly from requests in MicroSurvey’s Request Forum,” Sloman said.
New Network Plot Manager
A main feature of STAR*NET 8.01 is a new Network Plot Manager to control your observations. The network plot can be customized in an intuitive grid view that allows users to control the visibility, color, linetype and size of each network element to graphically differentiate conventional, GPS and leveling observations. Directional linetypes indicate the direction and number of observations between each network station. And, users can now use their mouse to smoothly zoom and pan within the network plot.
Michael Durnin, survey manager and technical manager with Murphy Surveyors, global consulting surveyors with offices throughout the UK and Ireland, and a STAR*NET user for 15 years, considers the new Network Plot Manager a valuable capability. “It’s very useful, and completely changes the approach and analysis I take with my network plots because I can more easily distinguish the types of observations in my networks and check for completeness and redundancy more easily.”
Errors Caught More Accurately
Establishing network control and checking it is a fundamental task on all projects. But now, STAR*NET has made this capability more versatile and powerful. “It’s the basis of our quality (in surveying projects) and the part of the fundamentals from which our precision on surveys is quoted,” Durnin explains. “All measurements are propagated from your control, so having a robust solution on which we (Murphy Surveys) can rely is the bedrock of our methodologies and protocols and how we achieve precise results. Least squares adjustment gives us this solution, allowing us to catch errors accurately and with confidence,” Durnin added.
Rail/control network projects have become a specialty of Murphy Surveys, and so STAR*NET already has proven its mettle when used for this application. For example, in 2012, Network Rail, the authority responsible for the UK’s railway network, opened what then was the landmark new London Blackfriars station to provide better interchange between national rail and London Underground services. The project’s aim also was to make London’s Bankside and South Bank areas more accessible to passengers. The project, whose surveying was performed by Murphy Surveyors, was part of the Thameslink Program, a 5.5 billion British pounds effort to improve travel running north to south through London.
During redevelopment of the Blackfriars station, Murphy Surveyors performed a laser scan survey to verify the positions of existing signage throughout the ticket halls to the north and south of the station and in the platform areas. Network Rail used the data to study the visibility of signage and to identify other areas of the station that could be improved. The data also was valuable for use alongside an existing design model so that a visual simulation of the passenger’s travel experience could be accomplished.
Level Loop Tolerance Check Added
Murphy Surveys performed a closed loop traverse to extend the existing control network within Blackfriars Station. A survey traverse was performed down the stairs into the northern and southern ticket halls of the stations and back up alternate routes and onto the station platform. This enabled Murphy Surveys to create the needed closed loop. Additional cross-bracing measurements were also made to strengthen the network. These measurements were processed with STAR*NET, after which each newly installed railway station was given a level loop tolerance check to ensure accuracy. The leveling data was fed into STAR*NET so it could be included in the adjustment (in the new STAR*NET version 8.1, a new Level Loop Tolerance Check allows users to instantly verify the vertical closure of level loops or traverses).
More Streamlined Workflow
For the Blackfriars Station survey, Murphy Surveys used a Leica 6200 HDS laser scanner at numerous locations to capture sufficient data. Also used was a Nodal Ninja bracketing system and a single-lens reflex camera to color the scans. Murphy Surveys delivered the scanned data with light intensity and DWG TrueView as required by Network Rail and as part of a full survey report that also contained witness diagrams, traverse adjustments, etc.
Projects like Blackfriars Station are now easier to measure using STAR*NET 8.1 because the software gives consistent measurements over the lifecycle of a project from field to finish, which could take from months to years. “During construction of a project, points are destroyed and replaced,” Durnin explained. “STAR*NET allows us to keep the network consistent and homogenous. For construction with a BIM, the ability to retain the spatial data capture and stake out consistent course of the project is key.” For example, Durnin added, a network of stations that are all linked to the original control and from which the design is based is crucial. “Maintaining consistency in the control network and monitoring the quality of measurements during stake-out or as-built survey (i.e., TPS, GNSS, or HDS) is key to successful survey results and a streamlined workflow that reduces risk,” Durnin said. Least squares adjustment produces this kind of result.