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I've created some polygons with Google Earth which I'd like to convert to my flat map's coordinate system.

I've loaded a few shapefiles into QGis of a county's roads, parcels, etc. The coordinate system for these points is projected using the "NAD83(HARN) / South Carolina (ft)" or "EPSG:3361" standard.

Next I load a kml file into QGis created using Google Earth Pro which is composed of a Polygon of geographic (lon/lat) points.

QGis is clever and has perfectly overlaid the geographic-points polygon directly where it should be on the flat/projected-points polygon. I can hover my mouse around and see the projected coordinate points where my polygon's exterior ring resides.

I want to export the points of my geographic-polygon into the projected coordinate system that the rest of my qgis map is based on. This is because all of my county data shapefiles are projected, that and PostGIS doesn't seem to allow me to do spatial joins of two geographic polygons...

Anyway, I right click on the imported vector layer (Google Earth-gen'd polygon) and click 'Save As'. (I've already enabled 'On the Fly CRS Transformation')

The plan is to export the polygon into projected coordinates, so I choose 'Selected CRS' and locate my proj4 code which is for SRID:EPSG-3361.

Exporting this does not accomplish my goal. The exported kml still contains geographic coordinates. QGis seems very capable of doing what I want to do, its overlaid two layers from entirely different coordinate systems. How might I go about transforming this clearly-understood (by qgis) polygon into the projected coordinate system upon which it apparently lies?

UPDATE 1: - I created a second layer whose chosen CRS is the projected one, redrew a similar polygon on top of the imported one, and tried to export it, using, again, the projected coordinate system. IT ALSO got exported into geographic coordinates!

UPDATE 2: I exported a shapefile of the county this time and IT TOO got exported into geographic coordinates!!! This tells a lot about the nature of the problem. Everything is being exported into geographic coordinates. Could it just be the fact that I'm using kml?

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1 Answer 1

Kml has always degrees as units, so you will have no luck with that format.

Exporting as shapefile should work. Note that you have to choose the CRS again (QGIS does not remember it from the last export).

Can you add the shapefile to the canvas, and look up the extent under properties, metadata tab? Furthermore, you can open the .prj file that was created along with the shapefile. It should contain the projection data for NAD83(HARN) / South Carolina (ft).

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In PostGIS use ST_Transform(geometry g1, integer srid) to convert between srids. –  simplexio Aug 16 '13 at 6:47
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In QGIS , select layer , right click , "Save as" and just under "Encoding" change "layer CRS" to "Selected CRS" and choose new srid –  simplexio Aug 16 '13 at 6:51

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