I created several functions to make regular grids based on the size of my document and a step to vary. See Let's Make Grids / neocarto / Observable. Now I want to overlay this grid on a world map and find out which cells overlap this world map (or simply which centroids are contained in the world map). See World Grids / neocarto / Observable. But it can’t work. Because my basemap is in geographic coordinates while the coordinates of my grid depend on the size of the page (because I want a regular grid whatever the projection). How to proceed? Any ideas would be welcome.
Is this what you are looking for? Examples · emeeks/d3-carto-map Wiki · GitHub
Not really. These materials are a bit old.
I sent you a suggestion. The idea is:
- use d3.polygonCentroid(gridCell) to compute the center of every grid cell (in pixels)
- use projection.invert([cx,cy]) to get the longitude and latitude for the grid cell center
- use geoContains to test if the center is in the land
geocontains can be very slow, see if you can draw the map once to canvas, and read the relevant pixels instead:
Thank you very much @Fil. I don’t have time to deal with it now. But I have added your comments to my notebook.