QGIS – Reprojecting from EPSG:3857 to EPSG:28992

coordinate systemepsggeopandasqgis

I'm attempting to reproject a coordinate in EPSG:3857 to EPSG:28992. The problem I'm running into is as follows:

When I use GeoPandas (ie. df.to_crs(epsg=28992)) to reproject my coordinates I get a value similar to this for my coordinate: (-587791.60, -5732776.63)

But when I go to the same coordinates (manually) in QGIS (with CRS set to 28992), and right click to get coordinates, the coordinates provided (in CRS 28992) are similar to this: (172839.93,442692.96)

How can I reproject in GeoPandas (or in any other Python library) to get (172839.93,442692.96) instead of (-587791.60, -5732776.63).

When converting a Polygon in GeoPandas and putting it into QGIS all measure of distance is lost (ie, a polygon that was a few km2, becomes a few mm2), but I'm not sure what I'm doing wrong. I've been googling for a few hours and I think it might have something to do with how the Datum is transformed, but I'm not sure what exactly that is nor how I can do it properly.

When I change the CRS to 28992 (I drag in OpenStreetMaps), I get the following prompt, which might have something to do with why the coordinates in QGIS are different from GeoPandas (again supporting my Datum transformation theory):

Best Answer

I managed to solve the problem by converting from EPSG:4326 instead of from EPSG:3857.

My understanding is that EPSG:4326 is a "flattened/map" version of EPSG:3857, so they are equivalent.

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[GIS] How to change an existing srs in QGis

Are you sure that your Postgis and QGIS share the same +towgs84 parameters?

My QGIS 2.0.1 Dufour comes with this definition:

+proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889 +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel +towgs84=565.417,50.3319,465.552,-0.398957,0.343988,-1.8774,4.0725 +units=m +no_defs

while my PostgreSQL has this stored in table spatial_ref_sys

+proj=sterea +lat_0=52.15616055555555 +lon_0=5.38763888888889 +k=0.9999079 +x_0=155000 +y_0=463000 +ellps=bessel +towgs84=565.237,50.0087,465.658,-0.406857,0.350733,-1.87035,4.0812 +units=m +no_defs

If your QGIS has another proj definition for EPSG:28992, your installation might be broken. Have a look at the setup log if postinstall was broken somewhere.

One other point: Postgis uses this string for the WKT definition:

PROJCS["Amersfoort / RD New",
  GEOGCS["Amersfoort",
    DATUM["Amersfoort",
      SPHEROID["Bessel 1841",6377397.155,299.1528128,
      AUTHORITY["EPSG","7004"]],
    AUTHORITY["EPSG","6289"]],
    PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],
    UNIT["degree",0.01745329251994328,AUTHORITY["EPSG","9122"]],
    AUTHORITY["EPSG","4289"]],
    UNIT["metre",1,AUTHORITY["EPSG","9001"]],
  PROJECTION["Oblique_Stereographic"],
    PARAMETER["latitude_of_origin",52.15616055555555],
    PARAMETER["central_meridian",5.38763888888889],
    PARAMETER["scale_factor",0.9999079],
    PARAMETER["false_easting",155000],
    PARAMETER["false_northing",463000],
    AUTHORITY["EPSG","28992"],
    AXIS["X",EAST],
    AXIS["Y",NORTH]]

which references to Amersfoort datum, but no +towgs84 are stored for that. I am not sure if QGIS therefore sets +towgs84 to zero, instead of using its own EPSG values, or those from the Postgis proj4 string.

QGIS writes this .qpj output:

PROJCS["Amersfoort / RD New",
  GEOGCS["Amersfoort",
    DATUM["Amersfoort",
      SPHEROID["Bessel 1841",6377397.155,299.1528128,
      AUTHORITY["EPSG","7004"]],
    TOWGS84[565.417,50.3319,465.552,-0.398957,0.343988,-1.8774,4.0725],
    AUTHORITY["EPSG","6289"]],
    PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],
    UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],
    AUTHORITY["EPSG","4289"]],
PROJECTION["Oblique_Stereographic"],
  PARAMETER["latitude_of_origin",52.15616055555555],
  PARAMETER["central_meridian",5.38763888888889],
  PARAMETER["scale_factor",0.9999079],
  PARAMETER["false_easting",155000],
  PARAMETER["false_northing",463000],
  UNIT["metre",1,AUTHORITY["EPSG","9001"]],
  AXIS["X",EAST],
  AXIS["Y",NORTH],
  AUTHORITY["EPSG","28992"]]

[GIS] Reprojecting vector layer from EPSG 3857 to 4326

I am not totally sure if I understand what you want to do. But when calling writeFeatures on a format, you can specify the dataProjection (the projection you want to have in your output format) and the featureProjection (the projection of your features that you want to export). See ol.format.GeoJSON.writeFeatures.

So for example if your features are in 'EPSG:4326' and you want to have a GeoJSON in 'EPSG:3857', you would do:

var geoJson3857 = new ol.format.GeoJSON.writeFeatures(features4326, {
  dataProjection: 'EPSG:3857',
  featureProjection: 'EPSG:4326'
});

Best Answer

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