Coordinate Systems and Drones


And now back to our regularly scheduled program… Have you heard of the drone invasion?

For those hiding under a rock because of the election, or other apocalyptic event,  drones have come to the forefront of data capture for many types of projects. Surveyors are actively digging into the technology to see how it can help them capture existing conditions quickly and at what quality they can capture.3DR and DJI are two companies that are offering drones to the commercial AEC industry.

For full disclosure, Synergis is now a partner with 3DR to provide the technology to our local customers.

The basic idea is the drone would fly a given area, take several pictures and upload that data to a cloud service to create composite imagery or elevation models. In order to accomplish this, All commercial drones have some sort of GPS recorder to stamp each image with coordinates. For clarity, this position stamp is rough in nature given the process described above and is typically within 5′ of the actual location. This is NOT acceptable to most survey firms for anything other than “napkin” sketched projects.

Many services have added the ability to add survey control to the process in order to tighten up the results. There is a best practices method to laying out the control over the capture area. According to 3DR, they can improve the location (x,y) accuracy of their data to within an inch!

In order to accomplish this correction, one bit of information is the need to have an EPSG code to identify the control’s coordinate system.Simply search by state or other information to find the EPSG code. For future reference, here are a few local codes to Pennsylvania and New Jersey.

 State  Coordinate System  Unit  EPSG Code
NJ  NAD83  Ft 3424
 NSRS2007  Ft  3616
 NAD83/2011  Ft  6527
PA NAD83 North  Ft  2271
NAD83 South  Ft  2272
NSRS2007 North  Ft  3650
NSRS2007 South Ft 3652

In case you need to transform your control coordinates, there is a great tool in that same website to re-project your coordinates from one system to another:

https://epsg.io/transform#s_srs=4326&t_srs=3857

Lastly, if you have Recap 360 Pro, there is a setting to specify the coordinate system. In that setting you use a portion of a typical code (PA83 for instance) and get results which also include the EPSG code.

snag-0216

Until next time…

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About Kevin
Hi… I am a husband, father, brother and neighbor. I am employed as a Civil Engineer and have enjoyed playing the drums for the last 30+ years.

2 Responses to Coordinate Systems and Drones

  1. Craig says:

    There is actually A LOT more that needs to happen then “just identifying the EPSG code.”

    EPSG is a voluntary registry of coordinate systems on a planetary scale. Having or NOT having the EPSG code has nothing to do with the quality of the horizontal control what so ever.

    How these vendors get away with making statements like “within an inch” of accuracy is mind boggling.

    Why authors and marketers continue to spew nonsense is also baffling.

    Like

    • Kevin says:

      Hi Craig. The EPSG code does not “correct” nor “make accurate” the data that’s collected. That is a separate discussion for sure. What i did not clearly describe in the article is how 3DR is re-positioning or rubbersheeting the data into the correct location. In fact, their adjustment is only 2D at this moment. If you were to take the photos and push them manually through recap pro, you could do a 3D adjustment.

      The quality of the photo, the placement of control, the overlap of imagery, etc. is what generates the stitched TIF or point cloud.

      While I do not qualify their accuracy claims, I would consider the data better than typical aerial topography flown at much higher elevations. Consider the tools and validate the output. That is the method with which we address ALL technological advances. Certainly blind trust is disastrous.

      Thanks for a great comment!
      Kevin

      Like

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