Overview ¶

The author needed to convert coordinate reference system (CRS) parameters for a TileMill project intended for use within QGIS as a tile layer. The conversion involved transforming bounding box data from EPSG:4326 (Geographic coordinates) to EPSG:3857 (Spherical Mercator projection).

Solution ¶

According to the post, “It really is quite trivial to do arbitrary once-off things in QGIS if you roll up your sleeves and get to grips with the python API!”

The author provided this Python code for the QGIS console:

box = QgsRectangle(-19.6875,-37.9962,59.0625,37.4400)
source_crs = QgsCoordinateReferenceSystem(4326)
dest_crs = QgsCoordinateReferenceSystem(3857)
transform = QgsCoordinateTransform(source_crs, dest_crs)
new_box = transform.transformBoundingBox(box)
new_box.toString()

Output ¶

u'-2191602.4749925746582448,-4578889.0142234507948160 : 6574807.4249777207151055,4500615.8633687794208527'

The demonstration illustrates how QGIS’s Python capabilities enable straightforward geospatial coordinate transformations without external tools.