This project is read-only.

What is a "projected X (or Y) map coordinate"?

Jun 17, 2015 at 1:32 PM
Hello,
I understand what are Longitude and Latitude, what are coordinates in pixels, but what is a "projected X (or Y) map coordinate"?
For example I take a point with Longitude = 37.731 and Latitude 55.709 and axMap.DegreesToProj gives me X = 4200195.70 and Y = 7500702.55.
But what are these numbers? Are they some meters, millimeters or what? )
I did not find an answer in MapWinGis documentation.
Thank you.
Jun 17, 2015 at 3:52 PM
They are units defined by coordinate system & projection of map (see AxMap.GeoProjection.ExportToWkt()), which in turn is usually borrowed from the first datasource which is added to the map. If it's WGS84, they are degrees. For UTM or Web Mercator they are meters. In your case they are most likely meters. It's rather uncommon to see units other than decimal degrees or meters.

The important thing is that these coordinates are projected, which means that because of the distortions introduced by projection they often aren't equal to the units on the ground. If you are using correct UTM zone they will be close to the reality, but Web Mercator, for example, introduce larger distortions the further from the equator you go. Therefore for correct calculations of distance and area it's recommended to use AxMap.GeodesicDistance, AxMap.GeodesicArea.

Hope it helps,
Sergei
Marked as answer by Swift62 on 6/17/2015 at 8:48 AM
Jun 17, 2015 at 4:03 PM
Thank you, Sergei!