X marks the spot for aerial maps
The Minnesota Department of Transportation has a small window of opportunity when it comes to aerial mapping, and that window is about to open.
The snow is about to melt away (hopefully) and the trees have yet to start budding, leaving a view from the sky wide open.
“MnDOT contracts for aerial photography most years to create a record of what is in place now,” District Land Surveyor Tom Harper said.
That photography could be used for future projects, determining drainage areas, wetlands and more.
“The engineers decide where projects are coming,” he said, adding that they look five years ahead on projects.
Survey crews then determine where the targets, or X’s, should be placed.
“The targets show up in the photographs and are then used to align and scale the photography” he said.
If the target happens to be on a paved surface, crews paint a large white X. If it’s not on a paved surface, in a ditch or in a field, then fabric X’s are put in place.
A survey crew then records the coordinate position and elevation of these targets and provides that information to the aerial photography company.
“We save a lot of time and money if we can do it by airplane,” Harper said.
Since it’s not feasible for MnDOT to own a plane and have someone who takes the pictures in the three week window of opportunity in the spring and about one week in the fall, the entity contracts for the service. Harper said the state office contracts with an aerial photographer to take the photos throughout the state as needed.
He said the photographers are usually from the south because they obviously have much more opportunity because of the better weather conditions.
“Whatever you see from 2,500 feet is what we get a picture of,” Harper said.
Not only does Harper send his mapping requests to the St. Paul office to get the aerial photos, the state office also tells the regional office where to put the targets for the project. The local office then checks the spot and adjusts it as needed if it interferes with someone’s property.
“We try to look at where we’re not being too intrusive,” he said.
That’s not to say a cloth target won’t end up in someone’s field. But, he said, they try to get the mapping done before the farmers need to be in their fields. If it doesn’t work out, the targets can be adjusted with a call to the MnDOT office.
The targets can be placed up to a quarter of a mile from the center of what is being photographed.
“By targeting the photographs, the aerial mapping created becomes much more accurate than that available through other free venues on the Internet,” Harper said.
He said MnDOT is adamant about getting the word out before the targets are in place because the one year they forgot, he got calls. One person even feared the Ku Klux Klan had placed the white cross (though it was an X) on their property.
When there is a major project completed, like the Highway 10 realignment in Detroit Lakes for example, MnDOT will take an “as built” aerial shot since there was such a large change from the original road to after the project.
There are other areas, he said, that aren’t photographed for years at a time because of little change over the years. While areas like Alexandria are done more frequently because of the frequent changes, places like Ulen may not be.
MnDOT workers will take the map with them and then “you can drive the road, look for changes and manually map the changes if needed.”
Upcoming aerial projects
Though this year there aren’t any mapping projects real close to Detroit Lakes, there are still several going on in the 12-county district the Detroit Lakes office covers.
Weather allowing, the targets will be placed near the end of March. Locations include:
- Highway 10 from Dilworth to Highway 9.
- Highway 12 from Highway 119 to Benson.
- Highway 27 from Traverse County Road 6 to Wheaton.
- Highway 28, Highway 29, Highway 55 and Highway 104 in the Glenwood and Starbuck areas.
- Highway 28 from Beardsley to Graceville.
- Highway 59 from Appleton to Highway 12.
- Highway 59 from Morris to the Grant County line.
- Highway 78 from Interstate 94 to Battle Lake.
MnDOT requests that landowners not remove or disturb the targets until the photography is completed. If a target must be moved, please contact MnDOT survey staff at 218-332-5644 or 800-657-3984.