Click in between point cloud to select pointcloud

Hi, I am an amateur at using three.js. I am currently working on a project where I have a set of points projected onto a surface in the shape of boxgeometries (with the center of the boxes being the vertex coordinates). All of these boxes are stored as a group geometry mesh. I would like to be able to select the entire mesh if the cursor clicks anywhere in between or on the mesh as shown in the picture. Any suggestion on how I can achieve this ?!

Note that I am already able to select the mesh if I click the mouse on the mesh boxes but I want to be able to extend this to mouse click even in between the boxes (that is in the grey area in between) . For this, I need to be able to acquire the boundary points of the mesh and if I can get only the boundary points then I can create a non visible mesh from this boundary and use it to be able to select the mesh points itself but I don’t know how to acquire the boundary points given a set of points.

The problem then boils down to a mathematical problem: Given a set of 2-D points, find the points that form an outline or boundary. I am hoping this is not the same as a Convex Hull problem as I could have points taking weird alignments too such as the one here: