Refactor SMRF code

* only write intermediate rasters for debugging when optional output directory is provided

* make program args more consistent with the paper

* revert from TPS interpolation back to average of 8 nearest neighbors

* use iterative morphological operations and diamond structuring element for speedup

* remove the classify/extract args, always classify, and extract with range filter if desired

doc/stages/filters.smrf.rst

@@ -6,20 +6,6 @@ filters.smrf
 Filter ground returns using the Simple Morphological Filter (SMRF) approach
 outlined in [Pingel2013]_.
 
-.. note::
-
-  Our implmentation of SMRF is in an alpha state. We'd love to have you kick
-  the tires and provide feedback, but do not plan on using this in production.
-
-The current implementation of ``filters.smrf`` differs slightly from the
-original paper. We weren't too happy with the performance of (our implementation
-of) the inpainting routine, so we started exploring some other methods.
-
-Some warts about the current implementation:
-
-* It writes a bunch of intermediate/debugging outputs to the current directory
-  while processing. This should be made optional and then eventually go away.
-
 .. [Pingel2013] Pingel, T.J., Clarke, K.C., McBride, W.A., 2013. An improved simple morphological filter for the terrain classification of airborne LIDAR data. ISPRS J. Photogramm. Remote Sens. 77, 21–30.
 
 Example
@@ -34,9 +20,12 @@ returns, writing only the ground returns to the output file.
       "pipeline":[
         "input.las",
         {
-          "type":"filters.smrf",
-          "extract":true
+          "type":"filters.smrf"
         },
+        {
+          "type":"filters.range",
+          "limits":"Classification[2:2]"
+        }
         "output.laz"
       ]
     }
@@ -47,20 +36,20 @@ Options
 cell
   Cell size. [Default: **1.0**]
 
-classify
-  Apply classification labels (i.e., ground = 2)? [Default: **true**]
-
 cut
   Cut net size (``cut=0`` skips the net cutting step). [Default: **0.0**]
 
-extract
-  Extract ground returns (non-ground returns are cropped)? [Default: **false**]
+outdir
+  Optional output directory for debugging intermediate rasters.
+
+scalar
+  Elevation scalar. [Default: **1.25**]
 
 slope
   Slope (rise over run). [Default: **0.15**]
 
 threshold
-  Elevation threshold. [Default: **0.15**]
+  Elevation threshold. [Default: **0.5**]
 
 window
-  Max window size. [Default: **21.0**]
+  Max window size. [Default: **18.0**]