Adding processing option to classify 16bit rasters using scaled value…

…s instead of raw values. (#5834)

Added processing option to classify 16bit rasters based on scaled value - includes a basic test.

mapdrawgdal.c

@@ -1933,6 +1933,9 @@ msDrawRasterLayerGDAL_16BitClassification(
   int lastC;
   struct mstimeval starttime={0}, endtime={0};
 
+  const char *pszClassifyScaled;
+  int bClassifyScaled = FALSE;
+
   if(layer->mask) {
     int ret;
     layerObj *maskLayer = GET_LAYER(map, msGetLayerIndex(map,layer->mask));
@@ -1996,6 +1999,13 @@ msDrawRasterLayerGDAL_16BitClassification(
     }
   }
 
+  /* -------------------------------------------------------------------- */
+  /*      Fetch the scale classification option.                          */
+  /* -------------------------------------------------------------------- */
+  pszClassifyScaled = CSLFetchNameValue( layer->processing, "CLASSIFY_SCALED" );
+  if( pszClassifyScaled != NULL )
+    bClassifyScaled = CSLTestBoolean(pszClassifyScaled);
+
   /* -------------------------------------------------------------------- */
   /*      Fetch the scale processing option.                              */
   /* -------------------------------------------------------------------- */
@@ -2104,12 +2114,17 @@ msDrawRasterLayerGDAL_16BitClassification(
 
     cmap[i] = -1;
 
+    // i = (int) ((dfOriginalValue - dfScaleMin) * dfScaleRatio+1)-1;
     dfOriginalValue = (i+0.5) / dfScaleRatio + dfScaleMin;
 
     /* The creation of buckets takes a significant time when they are many, and many classes
        as well. When iterating over buckets, a faster strategy is to reuse first the last used
        class index. */
-    c = msGetClass_FloatRGB_WithFirstClassToTry(layer, (float) dfOriginalValue, -1, -1, -1, lastC);
+    if(bClassifyScaled == TRUE)
+      c = msGetClass_FloatRGB_WithFirstClassToTry(layer, (float) i, -1, -1, -1, lastC);
+    else
+      c = msGetClass_FloatRGB_WithFirstClassToTry(layer, (float) dfOriginalValue, -1, -1, -1, lastC);
+
     lastC = c;
     if( c != -1 ) {
       int s;

msautotest/gdal/class16_classify_scaled.map

@@ -0,0 +1,48 @@
+#
+# Simple test of classification methods on a floating point input. 
+#
+MAP
+
+NAME TEST
+STATUS ON
+SIZE 400 300
+EXTENT 0.5 0.5 399.5 299.5
+IMAGECOLOR 255 255 0
+
+IMAGETYPE png8_t
+
+OUTPUTFORMAT
+  NAME png8_t
+  DRIVER "GD/PNG"
+  IMAGEMODE PC256
+  TRANSPARENT ON
+END
+
+LAYER
+  NAME grid1
+  TYPE raster
+  STATUS default
+  DATA data/float.tif
+
+  PROCESSING "SCALE=0,28"
+  PROCESSING "SCALE_BUCKETS=256"
+  PROCESSING "CLASSIFY_SCALED=TRUE"
+
+  CLASS 
+    NAME "red"
+    EXPRESSION ([pixel] < 50)
+    COLOR 255 0 0 
+  END
+  CLASS 
+    NAME "green"
+    EXPRESSION ([pixel] >=50 and [pixel] < 150)
+    COLOR 0 255 0
+  END
+  CLASS 
+    NAME "blue"
+    EXPRESSION ([pixel] > 150)
+    COLOR 0 0 255
+  END
+END
+
+END # of map file