Circle display on openlayers map (client-side vs server-side)

Question

I'm developing a webGIS website where I draw circles from two sources:

• a mapserver mapfile that "draws" them from PostGIS (red circles in image). The circles are created with ST_Buffer, eg

  ST_Buffer(ST_GeomFromText('POINT(A B)', 4326), 0.072414686825054, 'quad_segs=32')

My mapfile serves in 4326 and 3857.

• Via Openlayers (blue concentric circles in image), either via

  var wgs84Sphere = new ol.Sphere(6378137);
  new ol.Feature(ol.geom.Polygon.circular(wgs84Sphere, GPS_pos_4326, i * 5 * 1852, 64).transform('EPSG:4326', 'EPSG:3857'));

or via turf, then creating an OL polygon, by using turf's destination function.

I understand that projecting a circle in "Google Mercator" should produce ellipses when not on the equator, so the behavior is expected.

But how could I do the same thing via OL?

Answer 1

It seems that in web mercator circles must appear as circles (their only peculiarity being that they appear larger when moving to the poles). This is explained here: Tissot's indicatrix and for OL here: OL Tissot's indicatrix example

The way I overcame the problem was to insert all my geometries into PostGIS in web mercator and have the mapfile read them as such.

For this I used ST_Translate, eg

ST_Buffer(ST_Transform(ST_GeomFromText('POINT($lon $lat)', 4326), 3785), $rad, 'quad_segs=32');