trcloud.md

@@ -12,7 +12,8 @@ In the input file, set `ptracking = T`. The tracking cloud will be activated at
 
 The initial position of the tracking particles is determined by the injection box. Specify `trbox[xyz]min` and `trbox[xyz]max` for its extent. The box is filled either
  * **randomly:** Set `gridtrack = F` and `ntrp` for total number of particles.
- * **gridded:** Set `gridtrack = F` and `ntrp[xyz]` for the number of particles in each dimension.
+ * **gridded:** Set `gridtrack = T` and `ntrp[xyz]` for the number of particles in each dimension. This will create a simple cubic grid.  
+You can also set `trgrid_centerpt = T` to add an additional particle at the center of each particle cube, this will create a bcc-type grid and increase particle density by \~25%.
 
 #### Reference Values