Completed my first flight, aerial Mosaic seems to be 30 ft off other georeferenced imagery?


#1

I was kind of hoping it would be alittle more accurate than this, is it something that I may be overlooking?

I did my flight plan and bought it into ArcMap, the existing aerial imagery basemaps show that my drone imagery is about 30 ft off to the North of the existing imagery.

See image here of the difference http://i63.tinypic.com/2i1fred.jpg

Is there something that I am overlooking that would account for such a big difference?

I was using a Mavic Pro, no ground control points


#2

Hi @LukeEdAllen,

Thanks for finding our Forum and posting your question! The accuracy you see is expected without adding Ground Control Points to your map. The accuracy of your map also depends on the type of drone, camera, lens, altitude, overlap, and a number of other factors. For your own reference, Mavic Pro’s GPS is not the best for capturing accurate data compared to say, the Phantom 4 Pro. I encourage you to check out our guide on Accuracy to learn more about the factors affecting your accuracy.

Feel free to reply if you have any additional questions after reviewing our guides. :slight_smile:

Best,
Stephanie


#3

You can use ArcMap or Google Earth Pro to create 3m accurate GCP’s using existing objects/structures. This would greatly increase the horizontal positioning accuracy of your maps. You might also try QGIS.


#4

Thank you for your responses!

Chaco, I sent you a pm about making cps in arcmap to your inbox, hope this is ok!

Thanks again,

Luke


#5

@chascoadmin @stephanie

Thanks for the info on the limitations of the Mavic GPS, and the suggestion to use Google Earth “to create 3m-accurate ground control points using existing objects /structures.”

Would getting GCPs from Google Earth simply be a mater of to find the lat/long of a handful of suitable objects/structures, and entering them as the lat /long for the GCPs?

I would be grateful for any additional information you might provide that could help me to do this quickly and correctly. Thanks!


#6

@ntres

You could use Google Earth the way you described, and the maps would be great overlays if you wanted to put them back in Google Earth as KML/KMZ files, but as you said it would be at best +/- 3 meter accuracy at best. I would suggest using the website below and either get a true elevation benchmark form an Engineer and Municipality or use the elevation from the site and run an auto-level. You can get elevations for all of your points from the site, but I haven’t tried that so I don’t know how accurate it would be and how it compares to Google Earth. Makes sure you set it up to give you the decimal DDMMSS so you don’t have to do any conversions besides the ft to m elevations.

Things like manholes, inlets, corners of concrete structures and tract property fence posts (the bigger ones) are all great markers that should stand the test of time. Just make sure you pick the bottom of the post.

https://www.gps-coordinates.net/


#7

Oh, and on the site put the middle of the hand over the point you want. I wish it had a cursor that was more conducive to picking points, but I don’t think they meant it for accuracies like we are trying to achieve. I tried to click the same spot several times and all were within 18 inches of each other. You can also use this site to measure between two Lat/Lon sets of coordinates to double-check in the field.

https://www.movable-type.co.uk/scripts/latlong.html