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How to adjust z coordinate for GNSS derived drone DTM

DavidGodfrey2

Hi there,

I am in the process of learning how to work with UAV derived data in ArcGIS scenes, i ahve encountered a Z axis offset issue and was wondering how i can resolve this? The data is from a Lidar UAV and is GNSS WGS84 but when i view the data in a Scene there is a big offset as per the picture below! How do is resolve this?

This is the spatial reference i am using from the UAV DTM which is set as ground in a local scene

Thanks in advance - be kind please I'm quite new to this!

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JustinJohnston

I have had this issue in the past and it was a result of coordinate system difference between the scene and UAV data. For instance, the map might be in feet and the LiDAR in meters.

Also, not sure if it makes a difference, but I see you are using the UTM Zone Transverse Mercator projection. Not sure that is the same as the WGS 1984 Web Mercator that scenes uses. Others may know better than I.

Cheers,

Justin

DavidGodfrey2

Thanks Justrin for the quick reply - I have been using the define projection and trying different options but no luck!

The last iteration now looks like the below for the layer

JustinJohnston

What coordinate system is your scene using?

ThomasHoman

What is the difference in elevations? Were you expecting 1000 and got 3000?

JustinJohnston

It really looks like your LiDAR was created with the Z in feet and is being expressed with the Z in meters. The other change is whether it was made using MSL or Height Above the Ellipsoid vs WGS 1984. All of those mess with it. When I do photogrammetry, I make sure the products coming out of the processing software (DroneDeploy, Drone2Map, Pix4D, Site Scan, etc) are setup to create them using the WGS 1984 for Z.

Cheers,

Justin

DavidGodfrey2

Thomas @JustinJohnston

The diference is about 50m, i am reporcessing the data using new coordinate systems icnlduing one for z

I shall see how this goes and update!

DavidGodfrey2

Justin

Thanks - defo onto the issue here the Z was set at default so reprocessing now !

Dve

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