topic Re: Is it possible to calculate 3D geodesic length of a line? in 3D Mapping Questions

Is it possible to calculate 3D geodesic length of a line?

LeeDavis1 — Tue, 20 Dec 2016 17:33:07 GMT

I have LIDAR coverage for a route which crosses multiple UTM zones. I want to calculate the length of this route as accurately as possible correcting for projection error, elevation, and curvature of the earth. I have figured out the first two parts but the curvature issue has stumped me. By modeling the Earth in AutoCAD using UTM WGS 84 parameters I've come up with a length multiplier of 1.000457002 to account for curvature but I'm not sure if that is correct, or if that can be multiplied with a 3D length to get the proper answer.

All thoughts are appreciated.

Thank you,

-Lee

Re: Is it possible to calculate 3D geodesic length of a line?

DanPatterson_Retired — Tue, 20 Dec 2016 18:02:34 GMT

Add Geometry Attributes—Help | ArcGIS Desktop includes LENGTH_GEODESIC
LENGTH_GEO: The geodesic length of the line.

a search in the help returns the available options... key search words 'geodesic length'

even in the field calculator Calculate Field examples—Help | ArcGIS Desktop

Re: Is it possible to calculate 3D geodesic length of a line?

LeeDavis1 — Tue, 20 Dec 2016 18:20:05 GMT

Good tool I have used that one. Notice how it returns LENGTH_GEO & LENGTH_3D as separate values. I am looking for a way to combine the effects of 3D and geodesic into a single length measurement.

Could be possible to use this to get the % length added by geodesic and add that to the length 3d.

Thanks

Re: Is it possible to calculate 3D geodesic length of a line?

DanPatterson_Retired — Tue, 20 Dec 2016 18:27:32 GMT

It would be an interesting exercise. I doubt that most people have lines with sufficiently dense vertices to accommodate such calculations over long distances while accounting for the possible range in elevation errors over those same differences.

Re: Is it possible to calculate 3D geodesic length of a line?

LeeDavis1 — Tue, 20 Dec 2016 19:10:18 GMT

It is a unique problem. I am in the engineering business and these differences in length correlate to differences in material quantities, so we are talking about millions of dollars. Our data gets very detailed over long stretches of terrain.

Thanks,

Re: Is it possible to calculate 3D geodesic length of a line?

DanPatterson_Retired — Tue, 20 Dec 2016 21:19:04 GMT

It would be an interesting comparison to extract an elevation profile from a seamless DEM between two points at some distance and compare that to planar and geodesic length assuming flat terrain. A line of latitude or longitude (over 3, 6 ... degrees) would standardize the calculations from coordinates.