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Services

 

 

Ground Control for Mapping

The photogrammetric process for creating accurate mapping from aerial imagery relies fundamentally on accurate ground control. Terrasurv has performed ground control surveys in all 50 states and internationally for projects ranging in size from a few acres to over 20,000 sq miles, and for a variety of scales from 3 cm GSD to 1 m and greater.

LiDAR projects require both accurate ground control points (GCP) and checkpoints (CP) to verify the accuracy of the delivered product. Terrasurv has extensive experience establishing ground control for Lidar in an accurate and economical manner for a variety of clients including numerous large USGS 3DEP projects in both urban and remote areas.

Mapping control surveys are typically performed using Real Time methods including RTK over cell, using a Virtual Reference Station (VRS) network, or Trimble Real Time eXtended (RTX) methodologies. 

 

Terrestrial Laser Scanning

Terrasurv has been performing Terrestrial Laser Scanning (TLS) projects since first acquiring a laser scanner in 2006. Current equipment includes a Trimble TX8, capable of performing high density/high accuracy scanning and A Trimble SX10 which is used when less point density is required. Processing of the point cloud data is done using Trimble Realworks. Typical transportation uses include bridge clearances, pavement slope analysis for drainage, and topographic map preparation. Other uses include deformation analysis and as-built documentation.

 

Hydrographic Surveys

Terrasurv has been performing small scale hydrographic surveys since 2006 using single beam fathometers and small watercraft. Projects range from small stilling basins using kayaks to lakes/ponds up to 100 or more acres using motorized boats. In addition, a remote controlled vessel is available for use in dangerous or contaminated locations

 

Deformation Surveys

Structures constructed by man such as dams, building, bridges, etc are subject to loads which can deform the structure and can lead to failure. A deformation survey is a survey to determine if a structure or object is changing shape or moving. The three-dimensional positions of specific points on an object are determined, a period of time is allowed to pass, these positions are then re-measured and calculated, and a comparison between the two sets of positions is made. Deformation surveys are performed at periodic intervals to monitor the stability of structures and to give early warning of any unexpected behavior. Terrasurv has performed more than 350 deformation surveys on more than 40 locks and dams operated by the US Army Corps of Engineers. These surveys are custom designed for each structure to best monitor potential movements and take into account the type of structure (concrete, earthfill) as well as the past history of each. A typical monitoring project consists of a site visit to determine existing conditions and to plan the network. Pre-Analysis of each structure is preformed using the simulation function in least squares programs to design the most economical network which meets project specifications. Typical design accuracies are ±3 mm for concrete structures and ±1 cm for earthen dams. This information is then used in the office to plan a scheme of observations that will meet the required accuracy. Next, the field observations are performed. This data is then processed and adjusted in the office to yield data that can be used as a baseline for future observations or to compare against previous surveys.

Another type of deformation survey is the monitoring of ground subsidence above mining operations, such as salt and coal mines. These surveys are done using a combination of precise leveling, high accuracy traverse/triangulation, and GNSS Surveys.

 

Geodetic Control Surveys

A geodetic control survey consists of establishing the horizontal and/or vertical positions of points for the control of a project site. Terrasurv uses multi-constellation/multi-frequency GNSS receivers, high accuracy total stations, and geodetic leveling equipment to establish control networks. Terrasurv has calibrated invar leveling rods and has executed multiple second order leveling networks, several of which were submitted to the National Geodetic Survey for inclusion in the National Spatial Reference System (NSRS). See the Bluebook Services below for more information. All total stations used by Terrasurv are calibrated yearly on NGS Calibration Baselines (CBL).

 

Least Squares Adjustments

Least Squares Adjustments are a fundamental part of achieving the highest possible accuracies when performing Geodetic Control Surveys and Deformation Surveys. We have more than 35 years of experience in performing least squares adjustments on surveys of all kinds, including historic tape traverse data, triangulation networks, and data collected by others. Custom programming facilitates the intake of data in any readable format. Software used included Geolab and Starnet.

 

Bluebook Surveys

A bluebook survey is a GNSS or leveling survey performed to certain specifications which is formatted and submitted to the National Geodetic Survey (NGS) for inclusion in the National Spatial Reference System (NSRS). Terrasurv has performed dozens of GNSS bluebook surveys ranging from a single station to countywide networks of more than 400 stations, as well as providing processing and adjustments for submittal of projects observed by other agencies and companies. Leveling projects from a single reset station to a 130 mile second order level run and subsidence monitoring projects have also been submitted.