Terrain Changes Photographed For Mapping Revisions

By Andrew Gorosko

As Lemuel Golden Johnson, Jr, sees it, it’s a matter of “perspective.”

Or, more properly, a matter of dual perspectives.

By converting copious aerial photos, which are taken from two viewpoints, Mr Johnson is able to manufacture mapping that is sold to governments and businesses.

Golden Aerial Surveys, Inc, of Mt Pleasant Road in Hawleyville is in the business of aerial photography and photogrammetric engineering.

“Photogrammetry is the art and science of creating topographic maps from aerial photography,” explained Mr Johnson, the firm’s president.

Topographic maps symbolize the earth’s surface relief through curving contour lines that graphically link points of equal elevation.

Because sequentially exposed aerial photos contain overlapped images, stereoscopic instruments may be used to derive the topographic contour lines that symbolize three dimensionality. 

As part of the town’s plans to update its existing planimetric mapping, Golden Aerial had a Pennsylvania aerial photography firm produce a series of about 900 color digital aerial photos of Newtown last April.

Such aerial photos provide the base of visual information from which true-scale planimetric maps are created with photogrammetric tools. The aerial photos are geometrically corrected to eliminate various types of photographic distortion.

Planimetric maps are the graphical foundation of the town’s computerized geographic information system (GIS).

Film-based aerial photos were produced for the town in 2007 and in 2002, in color and in black and white, respectively. Using the digital color photos that were taken last April, Golden would revise the town’s planimetric mapping to accurately reflect current local surface features. The town’s existing planimetric maps are based on the 2002 photos.

The 900 aerial photos taken of the town in April will be electronically joined to form a seamless photomosaic image, which when viewed on a computer monitor appears to be one huge photo.

Those aerial photos were taken at a time of year when vegetation was dormant, providing overhead views unobstructed by foliage. The photos were taken when shadows were minimal to maximize the illuminated detail.

Taxing Work

Property tax assessment is a primary purpose for the town’s planimetric mapping.

Planimetric maps may show features such as topographic contour lines, roads, parking lots, buildings, stone walls, fences, streams, railroads, bodies of water, the edges of wooded areas, stormwater catch basins, and utility poles, among various other features.

Because such GIS mapping is computerized, various “layers” of detail, which contain specific sets of features, may be electronically switched on and off, as needed, to create customized images.

The web address maps.newtown-ct.gov provides public access to the town’s multilayered GIS.

The 2012 digital color aerial photos of the town provide much more visual detail than was provided by the 2002 black and white photos, making the identification of surface features simpler, Mr Johnson said.

Also, the 2012 aerial photos have finer detail than the state government’s aerial photography of Connecticut, which is available for use by municipalities, he said.

Some of the most notable local terrain changes during the past several years occurred at the town-owned core campus at Fairfield Hills.

Fairfield House, Bridgewater House, Greenwich House, Litchfield House, and Yale Laboratory have been demolished by the town. In those respective locations, now exist a baseball field, Newtown Youth Academy, parking lots, and vacant lots.

Steven Birney, the town’s GIS software specialist, said that the town plans to revise its planimetric mapping, as needed, to reflect the physical changes that have occurred on local terrain since 2002.

It is yet unclear how much of the town’s mapping will need to be updated, he said. The new photos will be compared to the older photos to identify the local areas that need revised mapping, he said.

Places such as the Upper and Lower Paugussett State Forests along the west bank of Lake Lillinonah and Lake Zoar, respectively, would not need to be updated, he said.

However, areas where development has occurred will be reviewed closely, he said.

After it is determined what areas need revised mapping, Golden would determine costs for such work, Mr Birney said.

Golden

“We’ve built our reputation on doing very accurate and complete work for clients,” Mr Johnson said of Golden’s photogrammetric specialty.

Mr Birney said, “His reputation is excellent. He does quality work,” adding that the local firm provides the town with good service.

Mr Johnson started the firm in 1984 in Southbury, moving to Hawleyville in 1989.

While in high school, Mr Johnson studied landscape planning, drafting, and cartography. He later worked as a civilian mapmaker for the US Army Corps of Engineers. He later decided that he wanted to work for himself and began his own photogrammetry firm.

“It’s been a very satisfying field for me. I’ve been in it 48 years,” he said.

The mapping produced by Golden for the town is used by many town agencies in their decisionmaking, Mr Birney said. The town’s Technology and GIS Department typically receives about 25 requests per month for GIS mapping or data, Mr Birney said.

Good data is needed for sound decisionmaking, Mr Johnson said.

When the town was planning its central sanitary sewer system about 20 years ago, Golden produced the mapping required for sewer construction.

In the event that a customer needs certain maps made quickly, Golden has had aerial photos taken of the entire state to have reference photos available for mapmaking projects, Mr Johnson said. Those photos were taken from 2001 to 2004.

The aerial photos of Newtown taken last April will be added to the 2007 and 2002 aerial photos now posted on the town’s GIS website. The GIS, which is cross-indexed, contains a variety of information on more than 11,000 local real estate parcels.