“To the Point” Geomatics Newsletter Fall 2020

By Seth Goucher, Director of Geomatics

This summer has seen many changes to typical everyday tasks, and as the world continues to change, Sebago’s Geomatics Team has spread its wings and expanded the breadth of technical services to the sky. Over the last few months, the Team has been refining the integration of UAV data information into terrestrial laser scan and traditional survey datasets. Incorporating UAV data has given the Team a new perspective on completing projects and the updated means and methods which the Team now deploys to effectively collect more site data, while further reducing time onsite. The Team has completed multiple flight missions for several challenging site projects this year.

Geomatics Newsletter
UAV flight & data capture of 8,000+ linear feet of beach for a loss or gain of sand baseline study – York, Maine

Waterville Arts Center

Location: Waterville, Maine
Client: OPAL Architecture, Belfast, Maine
Summary: In Waterville, an historic 30,000+ square foot arts center was slated for renovation as part of the City’s overall plan to revitalize the downtown area.

The multi-story building and attached City Hall were collected utilizing high definition laser scanning and digital models were generated from the resulting point cloud. The modeling included exterior detailing such as the iconic signage, architectural window details, and masonry detailing. The models will be used in the development of the renovation plans for the existing building and speed up the design process by providing an accurate and complete base model for the project design team.

Holland Tunnel Overhead Gantry

Location: Georgetown Fabrication Shop, Massachusetts
Client: Cianbro Fabrication Facility
Summary: Connecting New York City and New Jersey, the Holland Tunnel is a subterranean vehicle tunnel that runs under the Hudson River. Originally constructed in 1927, the tunnel was in need of updated toll collection methods to accommodate rises in traffic over recent years. The new toll gantry arms were fabricated and mocked up off-site by the Cianbro Fabrication Shop in Georgetown, Massachusetts to prevent unnecessary shutdowns of traffic, while the layout of the new mounting brackets took place.

With a required tolerance of 1/8” or less, Sebago Technics was retained by the fabricator to layout the location of a dozen mounting brackets on the assembled gantry. The steel construction, which is over 3’ in diameter and 129’ long, sits on baseplates that are 3” thick. This heavy-duty foundation allows the 18’+ tall vertical posts to accommodate the massive weight, as well as resist wind forces from passing cars and trucks. The mockup was fully assembled in an environment that simulates the exact field conditions at the Holland Tunnel in New York. Once complete, Sebago utilized High Definition Surveying to collect an accurate record of the gantry assembly to ensure that the fabrication met design standards and would function on site, as anticipated.

Brewer Bulkhead Facility Bathymetric Survey

Location: Brewer, Maine
Client: Cianbro Constructors, Brewer Maine
Summary: Sebago Technics was retained by Cianbro Constructors to produce an existing conditions plan of the Brewer facility for the existing site condition topography of the waterfront area, onsite Berth/bulkhead area, eroded shoreline cribbing, and under water riverbed topography out to 100 feet from the high-water line.

Using the methods of UAV photogrammetry, constrained with onsite GPS control and bathymetric surveying, Sebago Technics was able to document the site effectively within a single tide cycle. Photogrammetry was used to accurately measure features on and above the surface of the site, while GPS located bathymetric survey data was used to map underwater features and depth of the Penobscot river.

In order to perform the photogrammetric UAV survey, Sebago Technics utilized a Phantom IV UAV with onboard RTK and PIX 4D software to convert the collected aerial images into a point cloud format. Our high definition scanning team extracted the existing site condition geometry from the comfort of the office. The data used to create the bathymetric river bed surface comes from an echosounder (sonar), which is mounted beneath or over the side of a boat and “pings” a beam of sound downward at the seafloor or from the FURUNO sounding unit connected by remote GPS system.

Once both sets of data have been collected, they are combined into an AutoCAD surface and ultimately a PDF topography plan that the client will utilize for a shoreline erosion mitigation sheet pile wall design. A 3D digital surface is created from the combined bathymetric and photogrammetric data, which Sebago collected. This surface provided the client with a record of the site topography and accurately demonstrates the current condition of the riverbed, rather than an older depth chart or sounding navigation chart, which may not reflect an up-to-date depth of the Penobscot River.

Incorporated UAV and Terrestrial laser scan
Incorporated UAV and Terrestrial laser scan data above waterline elevation coupled with below waterline bathymetric sounding data.

For more information, please contact:
Seth Goucher
Director of Geomatics