[mkgmap-dev] DEM: performance with bicubic interpolation

Wed Jan 24 12:45:02 GMT 2018

Hi,

I have added more algorithms for testing, patch is attached. Patched 
mkgmap recognize following values for x-dem-interpolation:
bilinear
bicubic
bicubic-spline
bicubic-catmull
bicubic-hermite

I have prepared new set for testing:
http://files.mkgmap.org.uk/download/408/interpolation2.7z

For me bicubic-catmull looks like bicubic. Bicubic-spline looks inferior 
and bicubic-hermite gives weird results, maybe something is wrong.

Still bicubic interpolation looks the best.

-- 
Best regards,
Andrzej
-------------- next part --------------
Index: src/uk/me/parabola/mkgmap/build/MapBuilder.java
===================================================================

--- src/uk/me/parabola/mkgmap/build/MapBuilder.java	(revision 4081)
+++ src/uk/me/parabola/mkgmap/build/MapBuilder.java	(working copy)
@@ -227,6 +227,12 @@
 		case "bicubic-spline": 
 			demInterpolationMethod = InterpolationMethod.BicubicSpline;
 			break;
+		case "bicubic-catmull": 
+			demInterpolationMethod = InterpolationMethod.BicubicCatmull;
+			break;
+		case "bicubic-hermite": 
+			demInterpolationMethod = InterpolationMethod.BicubicHermite;
+			break;
 		case "bilinear":
 			demInterpolationMethod = InterpolationMethod.Bilinear;
 			break;
Index: src/uk/me/parabola/mkgmap/reader/hgt/HGTConverter.java
===================================================================
--- src/uk/me/parabola/mkgmap/reader/hgt/HGTConverter.java	(revision 4081)
+++ src/uk/me/parabola/mkgmap/reader/hgt/HGTConverter.java	(working copy)
@@ -47,10 +47,11 @@
 	private int statRdrNull;
 	private int statRdrRes;
 	private InterpolationMethod interpolationMethod = InterpolationMethod.Bicubic;
+	private double[][] interpolationMatrix = Cubic.BSPLINE;
 
 
 	public enum InterpolationMethod {
-		Bilinear, Bicubic, BicubicSpline
+		Bilinear, Bicubic, BicubicSpline, BicubicCatmull, BicubicHermite
 	};
 	
 	/**
@@ -139,7 +140,7 @@
 				if (InterpolationMethod.Bicubic.equals(interpolationMethod)) {
 					h = (short) Math.round(bicubicInterpolation(eleArray, qx, qy));
 				} else {
-					Cubic interpolator = new Cubic(Cubic.BSPLINE, eleArray);
+					Cubic interpolator = new Cubic(interpolationMatrix, eleArray);
 					h = (short) Math.round(interpolator.eval(qx, qy));
 				}
 				statBicubic++;
@@ -675,5 +676,17 @@
 
 	public void setInterpolationMethod(InterpolationMethod interpolationMethod) {
 		this.interpolationMethod = interpolationMethod;
+		switch (interpolationMethod) {
+		case BicubicCatmull: 
+			this.interpolationMatrix = Cubic.CATMULL_ROM;
+			break;
+		case BicubicHermite: 
+			this.interpolationMatrix = Cubic.HERMITE;
+			break;
+		case BicubicSpline: 
+		default:
+			this.interpolationMatrix = Cubic.BSPLINE;
+			break;
+		}
 	}
 }
