View from above: MnDOT to map Highway 10
At the beginning of April, if the snow is gone that is, the Minnesota Department of Transportation will begin placing targets along Highway 10 from the airport to Acorn Lake in preparation for aerial mapping.
This specific mapping on this 11-mile stretch is being done for two reasons, but the MnDOT photogrammetric office in St. Paul actually flies about 300 miles on average a year throughout the nine districts in Minnesota.
"In the new construction, it's what we call an as-built to document what was built," Jeremy Erickson, senior land surveyor in the Detroit Lakes office, said of the completed Highway 10 realignment project in that area.
"Also in that area, the city of Detroit Lakes is going to be developing some of those areas, and we would have mapping then that will be available to the city of Detroit Lakes or the county for any future development they do in those areas."
The mapping goes to Acorn Lake because last year MnDOT flew the area from Acorn Lake to Perham, and this way there won't be any gaps in the documented mapping.
Pete Jenkins, photogrammetric unit supervisor in St. Paul, said each district throughout Minnesota looks through its program as part of the planning process and decides which project areas need to be flown for aerial photography.
"There are two purposes for aerial photography," he explained. "One is what we call non-mapping and the other is mapping -- in other words, where we control the aerial photography flight we can produce a map. Or, if we just want pictures for documentation."
Both of those purposes are being used in the Becker County mapping. (There are four other mapping projects taking place in this district of MnDOT, which includes Becker County.)
The project runs three miles west of Highway 59 and eight miles east of Highway 59.
"That's flight miles because we over-extend, so it's a little more than road miles," Jenkins said.
The few miles west of Highway 59 is for planning due to the growth west of Detroit Lakes.
"We're anticipating more anyway. Development leads to additional things with the highway," Erickson said. "There isn't a specific plan now. With this mapping, it takes a year to get this mapping back to us. We want to have this stuff done ahead of the projects so when we start developing a project, we have the mapping up front to use as a tool in planning."
'X' marks the spot
"A target layout map is provided by Pete Jenkins' office. They give us a coordinate file. They look at topographic mapping from the USGS, and they try to place the targets on roads," Erickson.
The size of the "X" or "V," something that has an identifiable point that can be determined as the coordinate, depends on the height of the aircraft.
"If it's doing an engineering scale product or construction, they're generally about four to six inches wide, by two to three feet long -- each leg of the cross," Jenkins said. The lower you fly, the more accurate product you're going to get."
The office in St. Paul does all the contract work for the flying; they coordinate with the district surveyors to put the targets down. Surveyors will contact landowners if a target needs to be placed on their property.
"Aerial photography is far less obtrusive than having a survey crew tramp all through somebody's property. That can be a little unnerving," Jenkins said.
"Because you have to have the targets every so often and maybe don't have road, some will end up in someone's yard or on the edge of a field. But we try and keep them on roads if at all possible or in ditches," Erickson said.
All aerial mapping is done to a national standard. Accuracy is relatively good -- 95 percent of all test shots meet the national standard of 6 inches or less.
"Generally, we produce maps that are between about 25/100ths and 4/10ths. That's generally our range," Jenkins said.
The process is also very economical.
"If you were to send surveyors out to grab the amount of information we're going to do with aerial photography, the time savings is incredible," Jenkins said. He added that ground surveying is obviously more appropriate for small lots, but aerial mapping is better for big projects.
The surveyors of each district control the project based on the coordinate system they want to use, he said.
"We produce a map for their design, for what they want to do."
Some targets, like ones used for a Farmer Service flight, were much greater in size.
In 2008, Minnesota first participated in an absolute accuracy mapping for the farm agency -- flying at about 20,000-30,000 feet, "so those targets are huge."
During the Farmer Service Agency aerial, MnDOT actually partnered with the Land Management Information Center, so this was a multi-governmental agency effort. It was also a partnership with the counties -- 76 of 87 counties participated.
"It was one of the biggest multi-governmental partnerships that was done in recent history, all in an effort to basically check the accuracy of the Farm Service Agency. That had never been done in Minnesota before," Jenkins said.
"We do more than just supply photography for this. Because we are the only photogrammetric shop in all of the state agencies, we provide advice to other agencies as well.
Mapping a purpose
"Aerial photography is the base for all the maps that are created for construction plans," Jenkins said.
Many years before the Highway 10 project through Detroit Lakes, Jenkins' crew flew the job and shot the base map.
"From the photogrammetric base map, all other aspects of MnDOT add to that to create whatever it is they need. Whether it's the engineers drawing their lines for proposed roads, or whether it's the surveys base map that adds all of the property lines, whether it's the bridge base map to show all the bridge detail information," he said.
"Everybody adds to the photogrammetical base map, which is the very first map created so that everybody builds their information upon my product."
In some states, aerial photography is not done unless that specific project is authorized. In Minnesota though, the district makes the decision based on several factors. The district can either wait until the project is authorized and use the money dedicated for that project, or they can take a "little risk before the project is authorized in hope of getting money," he explained.
With the stimulus bill, for example, if a district has a small project they may have on the shelf but think there's a chance of some money coming for it, the district can advance the project by already having the mapping done.
"That's one of the great things about MnDOT's non-centralized version of the DOT. In some states, they have one office that takes care of everything statewide. With MnDOT having it diversely set, those people in the (districts) make the decision for their local folks," Jenkins said.
"Now, they don't go crazy, but they do selective projects ahead of schedule. Often times it's maybe just one project a year extra. It's not like it's crazy spending."
The recent stimulus package will go for projects that districts have wanted to do but put off for whatever reason.
"A lot of things that you wished you could get done but just couldn't are probably going to get done through this stimulus money. That's just my overall general feeling."
Photography usually starts in the southern part of the state first because the snow is gone sooner. Contract work is being done now while snow is still on the ground, so targeting and the flying can be done before the May 20 date, when farmers want their fields cleared of any targets for planting.
Weather is a big factor as well.
"We can only fly on clear days. There's got to be void of clouds. Planes have to fly when the sun's angle is close to being vertical, because you want to minimize the shadows," he said.
A camera is installed in the belly of the airplane, and there's a hole where the lens sticks through, or a sensor if it's done digitally.
Generally, Jenkins said, everything is still done with film. They then scan the film and do everything digitally from there. MnDOT is in the process of switching to digital, but file sizes for digital are so huge, it places too much strain on current computers and storage.
The photogrammetric department has been asked to continue with film until the infrastructure can handle digital. With all the economic issues though, it might be a couple years until that happens.
"We haven't reached the emergency level yet," he said with a laugh. "We can still do our jobs and still do it the same way, so they're asking us to continue until they take care of other needs first. We'll comply."