topic Re: Convert geographic units (decimal degrees) to meters in ArcObjects SDK Questions

Convert geographic units (decimal degrees) to meters

DimaShats — Tue, 02 Aug 2011 13:03:43 GMT

Hi,

My application uses ArcEngine 10.0. The spatial reference of the data is WGS84 Geo.
I need to calculate the distance between objects in meters. For this purpose i use pe_geodesic_distance function from pe.dll.
I need to perform queries "find all objects in 100 meters distance and azimuth 45 degrees" also.
For converting meters to map units (degrees) i use pe_geodesic_coordinate function from pe.dll.
I define the center point of calculation and find another point in given azimuth. After this action i calculate the distance in map units (degrees) between two points (simple Euclidean distance).

If i convert some distance from meters to map units and reverse (even if i define the same start point and azimuth) i get different values of input and output.

Am i wrong when i use simple Euclidean distance while meters->degree conversion?
Did anybody implement something like this?

Thanks advance,

Dima Shats ??? GIS Software Infrastructure Team Leader
Ness Technologies

Re: Convert geographic units (decimal degrees) to meters

DubravkoAntonic — Tue, 02 Aug 2011 18:31:23 GMT

Something is strange here, computers are deterministic, if you user same input and get different outputs.:confused:
Verify that points you use are using same spatial reference, use SnapToSpatialReference to be sure coordinates are within resolution and on the map grid.

Other approach is to create Line by points and get Length from line.

regards Dubravko

Re: Convert geographic units (decimal degrees) to meters

DimaShats — Thu, 04 Aug 2011 14:17:16 GMT

I said "If i convert some distance from meters to map units and reverse (even if i define the same start point and azimuth) i get different values of input and output."
It means when i convert 10000 meters to degrees and reverse i don't get 10000 meters as a result.

Off course the results i get is deterministic.

Re: Convert geographic units (decimal degrees) to meters

DubravkoAntonic — Thu, 04 Aug 2011 18:24:08 GMT

That is deterministic enough 🙂
Transformation and rounding at decimal places takes therir price.