Accuracy issues between data in QGIS and Google Earth

Question

Wondering if anyone can answer this question. I have a kml in Google Earth. When I import it to QGIS, and then import the Google Earth images they are in slightly different places. I used a QGIS plugin so maybe that is the issue. Potentially the plugin imports the terrain images incorrectly.

Google Earth - Original Zone 18M 209551.00 m E 9131622.00 m S

QGIS - First import (note, Zone 18M is not an option in QGIS...potential answer?) 209581.516575, -868393.873839 *I think the incorrect Y coordinate has to do with zone datum points, which typically have large offsets if I remember right. But look at the X coordinate, its 30 meters off! This is the main part of my question. Why are the x and y coordinates changing?

QGIS - Coordinates given at bottom of screen -77.633805064386,-7.847746027456, which when plotted on Google earth line up where the original google earth point was.

One last issue. I imported water data from divaGIS for rivers, and the river is definitely a km or so to the east of the google earth image river. Should I trust divaGIS data? They have a suspicious quantity available for free.

http://www.diva-gis.org/gdata

Thanks!

Answer 1

If you set the project CRS in QGIS to EPSG:32718 (UTM zone 18), you get the same coordinates as reported by Google Earth. You might get different results if you have chosen another CRS. There are several CRS that are called UTM 18S (=South), but only one is based on the WGS84 ellipsoid.

The negative Y coordinate looks like a UTM 18N (=North) CRS. For QGIS, only North/South is relevant, the other letters (like M) of the UTM system are not used.

For the diva-gis data: The data from there is heavily generalized, suited for continet scale maps. If you want morer accurate data, look into OpenStreetMap data sources.