From 4d02d9ae47019abba6447123b8d3b402a6d4b46c Mon Sep 17 00:00:00 2001
From: Russell Stanley <russell@ausocean.org>
Date: Mon, 10 Jan 2022 10:08:54 +1030
Subject: [PATCH] add standard deviation function

---
 turbidity/plot.go           | 11 +++++++++++
 turbidity/turbidity.go      |  2 +-
 turbidity/turbidity_test.go |  4 ++--
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/turbidity/plot.go b/turbidity/plot.go
index 1c950ec1..f0e49c13 100644
--- a/turbidity/plot.go
+++ b/turbidity/plot.go
@@ -34,6 +34,17 @@ import (
 	"gonum.org/v1/plot/vg"
 )
 
+// standarDeviation will return the standard deviation of a float slice
+func standarDeviation(slice []float64) float64 {
+	mean := average(slice)
+	variance := 0.0
+
+	for _, i := range slice {
+		variance += math.Pow(i-mean, 2.0)
+	}
+	return math.Sqrt(variance / float64(len(slice)))
+}
+
 // Normalize values in a slice between 0 and 1.
 func normalize(slice []float64) []float64 {
 	max := -math.MaxFloat64
diff --git a/turbidity/turbidity.go b/turbidity/turbidity.go
index 6315ed39..d5757441 100644
--- a/turbidity/turbidity.go
+++ b/turbidity/turbidity.go
@@ -141,7 +141,7 @@ func (ts TurbiditySensor) minMax(img gocv.Mat, xStart, yStart, xEnd, yEnd int) (
 		for j := yStart; j < yEnd; j++ {
 			value := float64(img.GetUCharAt(i, j))
 
-			// Check max/min conditions, zero values are ignored.
+			// Check max/min conditions, zero values are ignoredt to avoid divison by 0.
 			if value > max && value != 0.0 {
 				max = value
 			}
diff --git a/turbidity/turbidity_test.go b/turbidity/turbidity_test.go
index 82f38643..830c4866 100644
--- a/turbidity/turbidity_test.go
+++ b/turbidity/turbidity_test.go
@@ -76,7 +76,7 @@ func TestImages(t *testing.T) {
 		// Evaluate camera burst.
 		sample_result, err := ts.Evaluate(imgs[i])
 		if err != nil {
-			t.Fatalf("evaluation Failed: %w", err)
+			t.Fatalf("evaluation Failed: %v", err)
 		}
 
 		// Add the average result from camera burst.
@@ -86,7 +86,7 @@ func TestImages(t *testing.T) {
 	// Plot the final results.
 	err = plotResults(results.Turbidity, normalize(results.Sharpness), normalize(results.Contrast))
 	if err != nil {
-		t.Fatalf("plotting Failed: %w", err)
+		t.Fatalf("plotting Failed: %v", err)
 	}
 
 	t.Logf("Sharpness: %v", results.Sharpness)