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I was finally able to get a clearer picture with settings at :

ISO : 100

Shutter : 1/640

Aperture : 6.3

Regarding GSD, If I am flying at 30m(100Ft) calculator is showing I’m getting GSD : .82. For manhole covers on the road, do you believe this GSD to be adequate. I own a Phantom 4 Pro.


Hi Steve,

Let me give you an example. A GSD of .82 cm means that the distance between 2 pixels (the center of two pixels) is 0.82 cm on the ground. So if the size of the manhole is more than that (8.2 mm) it would be adequate.

Whether the GSD is adequate depends on your needs. Is the image resolution sufficient for your applications? If so then yes it is adequate. 


Are you trying to locate the position of the manhole or read what is embossed on it? A typical manhole is cover is 34 inches (86 cm) diameter. Your GSD of .82cm will produced +/- 105 pixels across the lid. Plenty of coverage for position. You could fly much higher if you are just locating manholes. At GSD .82cm, you will be able to locate rocks a little over 1 inch wide. 

No one can answer your question, if we don’t what your requirements are for these manholes. Your drone at 305m (1,000ft) has a GSD of 9cm (3.54 inches). That would produce 9 pixels across a manhole. The bottom line is that the closer your are, the more detail you get. How much do you need?


The attached picture is a manhole at GSD 1.89cm (.74 inches). You can tell it is a manhole, but you can’t read what kind it is.

Tommy, I did provide some info regarding what I was needed. I needed to provide to the client the wording that was on top of the manholes. I was able to accomplish this by flying lower. I was previously flying 85 to 125 agl which did not produce the results. I had to fly at 50 feet to be able to create a ortho mosaic I could zoom to see what wording was on top of the manhole.


Have you started new posts regarding the manholes? Because all I see you asking in this post is if .82 is adequate enough for manholes.