[GIS] Lat, Long to Point geometry in cartoDB

carto

Could any one give me some good flow in diagram of how lat, long information from a csv file is changed into a point in cartoDB. I am assuming it is being done with the help of SQL queries, but still is there any architectural diagram of the data flow in cartoDB?

Best Answer

If you have LAT and LON as decimal degrees (WGS84 / EPSG:4326) in your CSV, CartoDB should automatically recognize those values when you upload your table.

If your data is another coordinate system, you might have to project your data to WGS84 first, then export to CSV, THEN upload to CartoDB.

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you could use CartoDB SQL API to get that data

http://USER.cartodb.com/api/v1/sql?q=select st_y(the_geom) as lat, st_x(the_geom) as lon from TABLE

for example, using jQuery ajax:

$.get("http://USER.cartodb.com/api/v1/sql?q=select st_y(the_geom) as lat, st_x(the_geom) as lon from TABLE", function(data) {
  for(var i = 0; i < data.rows.length; ++i) {
     var row = data.rows[i];
     console.log("point", row.lat, row.lon);
  }
});

[GIS] generate spatial geom from lat lon points for map in PostGIS

I'm assuming that your input lat-long are based on the WGS84 datum. Making a point geometry under this assumption is as easy as using the ST_MakePoint() function:

The problem with ST_MakePoint() is that the geometry that is created does not not have a spatial reference. We can set the spatial reference by using the ST_SetSRID() function.

So the simplest way of making a point geometry in the correct spatial reference is to chain both these function calls like this:

--Return point marked as WGS 84 long lat
SELECT ST_SetSRID(ST_MakePoint(-71.1043443253471, 42.3150676015829),4326);

I just noticed that you have a table with columns "lat, lon, value". In that case, you can use the following query to get a point and value

SELECT ST_SetSRID(ST_MakePoint(lon, lat),4326) as the_geom, value from mytable;

Best Answer

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