How to convert latitude and longitude to x y coordinates (in meters)

Question

I had an excel spreadsheet that included latitude and longitude coordinates for a series of points. I created a shapefile in QGIS from this data and selected the correct CRS (NAD83 / Massachusetts Mainland / EPSG:26986 / units = meters).

Now I want to export the data back into a CSV Excel file with the coordinates listed in meters (not latitude and longitude). But every time I right-click the vector file and Save-As, the WKT coordinates are displayed as latitude and longitude.

Is there something I'm doing wrong in QGIS?

Answer 1

What I would do is create the shapefile first in WGS84. This creates a shapefile with geometry in WGS84 Decimal Degrees, and a good starting point for any dataset that originates from decimal degree coordinates.

Then, create a new copy of your data in EPSG:26986 by right-clicking the layer, Save as > then set the CRS to EPSG:26986.

Then when you save the projected layer back out as a CSV, your WKT coordinates will be in EPSG:26986.

Answer 2

Maybe not the answer you are looking for if you are strict about doing this in QGIS, but I do these kind of conversions in PostgreSQL/PostGIS. It is easy to install if you don't have it and makes life much easier when dealing with geometry, at least for me.

First create schema data as you don't want to put your data in public schema:

CREATE SCHEMA data;

Then create the table:

    CREATE TABLE data.table_name
(
  id serial NOT NULL,
  lat double precision,
  lon double precision,
  other_field text,
  geom geometry(Point,26986),
  CONSTRAINT table_name_pkey PRIMARY KEY (id)
)

You can include more fields according to your input file, just use correct types. Next step is to import the data into the table:

COPY data.table_name(lat,lon,other_field) FROM '/home/dejan/test.csv'  DELIMITER ',' CSV HEADER;

Of course, use your fields and path. Use HEADER if you have header in your input, like in my sample:

lat,lon,other_field
23,-79,test1
23.5,-79.5,test2

Create the geometry with desired EPSG:

UPDATE data.table_name set geom=ST_Transform(ST_SetSRID(ST_MakePoint(lon, lat),4326),26986);

And now you can convert to any EPSG available in PostGIS or custom added and export the coordinates:

select ST_X(geom) as long, ST_Y(geom) as lat, other_field from data.table_name;

pgAdmin can help you with some of these steps through graphical interface.