| GIS Advances Hydrographic Survey
US Army Corps of Engineers lauds transition results
By Kevin P. Corbley The U.S. Army Corps of Engineers is saving taxpayers millions of dollars by making the transition to a completely digital GIS environment for its surveying and map production projects in the Atchafalaya River basin of Louisiana.
The Atchafalaya is a 182-mile-long, navigable distributary of the Mississippi River with a basin covering more than one million acres. The Corps' New Orleans District built and maintains a series of levees that protect the alluvial valley and surrounding communities against flooding by confining flow to the leveed channel.
The District also built and operates the Old River Control and Auxiliary Control Structures which regulate the volume of water flowing out of the Mississippi and into the Atchafalaya. The District has overseen production and publication of an Atchafalaya River Hydrographic Survey book on a 10-year cycle since the 1950s, and the Atchafalaya Navigation Folio every 2-years since 1987. Both have traditionally been published in hard copy formats similar to travel atlases, and each required resurveying and mapping of appropriate river features prior to publication.
"In 1991, the Corps went digital with its Mississippi Hydro book," said Ralph Scheid, a civil engineer in the District's Engineering Systems and Programming Section. "It was a big success in terms of the substantial reuse of digital data files for other projects."
When it came time to update the Atchafalaya hydro book in 1996, the Corps selected the contractor, 3001 Inc. of New Orleans, not only to perform digital mapping but also to create an entire GIS database for the river. By developing a complete GIS, the Corps gave itself the ability to update its map base continuously and generate revised map products as needed instead of on a strict 2- or 10-year cycle.
The savings in tax dollars will be realized most dramatically in the preparation of map products. The Corps will utilize an automated GIS feature extraction and map generation software package from Intergraph Corp. of Huntsville, Alabama, to create future editions of the maps after 3001 delivers the initial set.
To put the cost savings into perspective, the Corps spent $2.2 million for the surveying, mapping and publication of the Atchafalaya Hydro book alone in 1986 using traditional surveying and cartographic procedures. Beginning in 1996, the Corps budgeted a total of only $3.5 million for development of the GIS and creation of four separate map products, including the new hydro book.
"With a cost index applied to the 1986 project, it would have cost $3.37 million in 1996 dollars," said Scheid. "So with this project, it's as if we are spending the same amount of money, and we not only get a digital version of our hydro book, but three additional map products and a free GIS."
He added that, "Once it is finished, we will have created the definitive GIS of the Atchafalaya, and if we are efficient and keep updating it, we will never have to do another full-scale mapping or complete reproduction of the hydro and navigation books." Defining the Project
In 1996, the District awarded the project contract to 3001, a full-service mapping and GIS firm known for utilizing new and innovative surveying and cartographic techniques. The contract called for 3001 to develop an Atchafalaya Basin GIS compliant with Corps standards and four other hard- and soft-copy map products:
¥ Hydrographic Survey Book containing 137 cross-section and plan view maps of the river indicating exact depth measurements and showing precise locations of all natural and man-made river features associated with Corps' management of the river. Primarily used internally by the Corps, this product has become popular with engineering firms building marinas, docks, and moorings along the river.
¥ River Navigation Folio including 42 line maps detailing channel bottom and other river features affecting ship transportation along the river, such as wrecks, navigation lights, and buoy locations. These highly accurate maps are required in commercial vessels.
¥ River Basin Levee Base maps including 185 line maps representing a complete resurvey of monuments and stations along the entire Atchafalaya levee system.
¥ Orthorectified Photo Mosaic of the basin totaling 24 orthophotos and line maps.
Standards by which the Atchafalaya GIS has been developed were first devised by the Corps' Mississippi Valley Division for its Mississippi River database. The Division created a framework, called Regional Engineering and Environmental GIS (REEGIS), that dictates how the GIS will be populated.
The REEGIS schema is built around the Intergraph MGE GIS software and is becoming the defacto standard for GIS development within the Corps. It already has been adopted by six other Corps districts in the Eastern United States and is also being fully incorporated into a data dictionary effort called the Tri-Spatial Data Standards. "REEGIS enabled us to provide 3001 with a data dictionary, or template, so they knew exactly what layers and attributes to include in the GIS," said Scheid.
3001's Vice President of GIS Services, Jay Arnold, confirmed that REEGIS facilitates GIS population, "It tells us what feature should be collected, which GIS level it will be stored on, what color it will be depicted as, and what shape will represent it on the basemap." Mapping the Atchafalaya
"It made no sense to develop this new GIS by digitizing the old paper maps of the river," said Jeremy Conner, 3001 marketing director. "The river changes too much, which meant we had to conduct all new surveying and mapping for the entire basin."
Prior to the project, the New Orleans District had purchased complete aerial photographic coverage for the river basin. These were provided to 3001 for orthorectification and used in creating the Photo Mosaic product. The up-to-date photos also assisted 3001 in directing its field mapping efforts, which were complicated due to the harsh basin environment.
"The basin is essentially a swampy willow forest," said Stephen Hebert, senior vice president at the firm. "We had to use a mix of old and new mapping techniques."
To complete the hydrographic survey, the firm used a fleet of 20- and 40-foot vessels equipped with GPS and sonar. The boats traversed the river perpendicular to the channel while the sonar took 10 soundings per second off the river bottom to determine its depth. The GPS was tied into the sonar and tracked the boat location, creating a continuous map of the muddy floor.
The survey boat stopped at each buoy, light, mooring, wreck, and hazard to record its exact location by GPS for inclusion in the database.
Crews used traditional leveling equipment to survey from the surface of the river, up the bank and into the surrounding marshlands. This was called the overbank survey. Traditional survey equipment was employed instead of GPS for much of the overbank work because the density of the vegetation in the wetlands made adequate GPS reception difficult.
"We are developing an airborne LiDAR (Light Detection and Ranging) system for topographic surveying in these inaccessible environments," said Hebert. "It could reduce the cost of a survey by 75% and cut the field time from 1-year to 1-week."
The Corps also requested that the contractor resurvey the station markers on the levees which had been rebuilt and regraded several times in 25 years. Most markers were lost, so 3001 drove All-Terrain Vehicles equipped with Trimble dual-frequency GPS receivers along the tops of all levees to establish new coordinates and markers.
Data from each of the survey phases were entered into the appropriate levels of MGE, building the GIS database piecemeal as the mapping progressed. Generating Map Products
The existence of a multi-feature Atchafalaya River GIS has enabled the Corps and 3001 to completely automate the map production phase of the project. All of the features needed to create the four different types of map products are contained within the GIS database.
"We have more than 400 individual maps to make, and the GIS has dramatically accelerated the workflow," said Jeff Lower, 3001's Operations Manager.
3001 has integrated Intergraph's Map Finisher and Map Publisher software into the GIS to give the system a built-in cartographic output capability. The Corps will continue to use these functions for periodic generation of updated maps long after the first sets of digital maps are delivered by the contractor in the summer of 1998.
"This elevates the system beyond a mere GIS and converts it into a high-level cartographic production system," said Lower. "This really gives the Corps some options it didn't have before."
3001 technicians have written customized routines in Map Finisher to search the GIS and extract just those features needed for any given map. To create a Navigation Folio sheet, for instance, Map Finisher would retrieve river bottom depths, channel dimensions, buoy locations, and other information captains need to guide their ships safely down the river.
"Without the automated extraction, we would have to go through each DGN file in the GIS and manually extract features one by one," said Lower. "The real time savings is that we can run the batch program overnight to extract maps for the next day's production."
In addition to pulling the appropriate features out of the database, the software allows the technicians to add grids, ticks, labels, and map legends directly to the feature output file and change symbology and shapes as desired for the final map. Another script then converts each map feature vector into a raster file.
"Once the raster files are made, we batch process them through Map Publisher to create the final lithographic separates," said Lower.
Map Publisher software arranges the raster files into their proper layers, colors and patterning. It outputs digital files that are the equivalent of color film separates used for mass printing. The Corps plans to ship the digital lithographic files to a U.S. Government Printing Office for generation of future hard copies. More Products Planned
The Corps has traditionally made hardcopy versions of the Navigation Folio and Hydrographic Survey Book available for sale to the general public. Many end users, such as river boat captains and civil engineering firms, have recently converted to digital environments as well, which has prompted the New Orleans District to consider adding digital product lines as well.
"The Corps anticipates preparing the map products on CDs for distribution," said Scheid, "and we will put the entire GIS on CD for distribution to electronic chart vendors who create value-added navigation products for ship captains."
Another option the District may pursue is publishing all or part of the Atchafalaya GIS data on an intranet or Internet. That would make the information available to other Corps offices as well as to the general public.
"We are really optimistic this investment will pay for itself many times in the future because the GIS allows us to reuse data," said Scheid. About the Author:
Kevin Corbley is a freelance writer and consultant specializing in GIS, remote sensing and GPS. He is located in Denver, Colorado, and may be reached at 303-722-0312 or by email at [email protected]. Back |
