I am having GPS and SFM (Structure for motion) trajectory in UTM coordinates. I wanted to convert the both trajectory to NED (North East Down).

Method 1

In First step: I converted the data from UTM ---> Lat, Long, Height

In second step: Lat, Long, Height ----> NED.

Method 2:

As another method I took the first data from SFM in UTM coordinate as reference. Then I subtracted the first data [easting, northing, height] from all other points. So, I got the data in meters.

The same data point [easting, northing, height] again subtracted from GPS data points. The GPS data is in now meters.

The plots looks as following:

Which method is correct for conversion of data to NED??

Because method 2 data is matching what the plot should look like in UTM!!

Whereas method 1 might have precision problem due to two conversions, that's why the both data are close and seems overlapping each other. But that is not the case with original data.

Can somebody please suggest the best method to convert UTM to NED frame??