use an interface function node_extent instead of GI.extent

This allows us to perform any STI compatible algorithm on trees that do not have extents but some other kind of extent like thing....like spherical caps!

Author: asinghvi17

src/utils/SpatialTreeInterface/SpatialTreeInterface.jl

@@ -6,7 +6,7 @@ import Extents
 import GeoInterface as GI
 import AbstractTrees
 
-# public isspatialtree, getchild, nchild, child_indices_extents
+# public isspatialtree, getchild, nchild, child_indices_extents, node_extent
 export query, do_query
 
 # ## Interface
@@ -66,11 +66,29 @@ isleaf(node) = error("isleaf is not implemented for node type $(typeof(node))")
 Return an iterator over the indices and extents of the children of a node.
 
 Each value of the iterator should take the form `(i, extent)`.
+
+This can only be invoked on leaf nodes!
 """
 function child_indices_extents(node)
     return zip(1:nchild(node), getchild(node))
 end
 
+"""
+    node_extent(node)
+
+Return the extent like object of the node.  
+Falls back to `GI.extent` by default, which falls back
+to `Extents.extent`.  
+
+Generally, defining `Extents.extent(node)` is sufficient here, and you
+won't need to define this
+
+The reason we don't use that directly is to give users of this interface
+a way to define bounding boxes that are not extents, like spherical caps 
+and other such things.
+"""
+node_extent(node) = GI.extent(node)
+
 # ## Query functions
 # These are generic functions that work with any spatial tree type that implements the interface.
 
@@ -92,7 +110,7 @@ function do_query(f::F, predicate::P, node::N) where {F, P, N}
         end
     else
         for child in getchild(node)
-            if predicate(GI.extent(child))
+            if predicate(node_extent(child))
                 @controlflow do_query(f, predicate, child)
             end
         end
@@ -156,20 +174,20 @@ function do_dual_query(f::F, predicate::P, node1::N1, node2::N2) where {F, P, N1
         end
     elseif isleaf(node1) # node2 is not a leaf, node1 is - recurse further into node2
         for child in getchild(node2)
-            if predicate(GI.extent(node1), GI.extent(child))
+            if predicate(node_extent(node1), node_extent(child))
                 @controlflow do_dual_query(f, predicate, node1, child)
             end
         end
     elseif isleaf(node2) # node1 is not a leaf, node2 is - recurse further into node1
         for child in getchild(node1)
-            if predicate(GI.extent(child), GI.extent(node2))
+            if predicate(node_extent(child), node_extent(node2))
                 @controlflow do_dual_query(f, predicate, child, node2)
             end
         end
     else # neither node is a leaf, recurse into both children
         for child1 in getchild(node1)
             for child2 in getchild(node2)
-                if predicate(GI.extent(child1), GI.extent(child2))
+                if predicate(node_extent(child1), node_extent(child2))
                     @controlflow do_dual_query(f, predicate, child1, child2)
                 end
             end