uses various sampling strategies to create dummy nodes for the tnss_tree

```
tnss_dummies(
xy,
root,
circ = TRUE,
line = TRUE,
diag = TRUE,
grid = FALSE,
rand = FALSE,
ncirc = 9,
rcirc = 2,
nline = 10,
ndiag = 50,
ngrid = 50,
nrand = 50
)
```

- xy
coordinates of "real" nodes

- root
root node id

- circ
logical. create circular dummy nodes around leafs.

- line
logical. create dummy nodes on a straight line between root and leafs.

- diag
logical. create dummy nodes diagonally through space.

- grid
logical. create dummy nodes on a grid.

- rand
logical. create random dummy nodes.

- ncirc
numeric. number of circular dummy nodes per leaf.

- rcirc
numeric. radius of circles around leaf nodes.

- nline
numeric. number of straight line nodes per leaf.

- ndiag
numeric. number of dummy nodes on diagonals.

- ngrid
numeric. number of dummy nodes per dim on grid.

- nrand
numeric. number of random nodes to create.

coordinates of dummy nodes

```
# dummy nodes for tree rooted in California
xy <- cbind(state.center$x,state.center$y)
xy_dummy <- tnss_dummies(xy,4)
```