--- a/pkg/mesh/raster.go	Sat Aug 06 00:46:21 2022 +0200
+++ b/pkg/mesh/raster.go	Sat Aug 06 02:09:57 2022 +0200
@@ -26,6 +26,8 @@
 	"gemma.intevation.de/gemma/pkg/wkb"
 )
 
+// Raster represents a 2D cell raster with a given extend.
+// The cells are equally sized in X and Y direction.
 type Raster struct {
 	BBox     Box2D
 	CellSize float64
@@ -36,6 +38,8 @@
 
 const noData = -math.MaxFloat64
 
+// NewRaster creates a new Raster with the given extend
+// and cell size.
 func NewRaster(bbox Box2D, cellSize float64) *Raster {
 
 	width, height := bbox.Size()
@@ -61,6 +65,9 @@
 	}
 }
 
+// Rasterize fills the raster with the evaluation data
+// received via the given eval function. The cell values
+// 4x oversampled,
 func (r *Raster) Rasterize(eval func(float64, float64) (float64, bool)) {
 	var wg sync.WaitGroup
 
@@ -117,6 +124,9 @@
 	wg.Wait()
 }
 
+// Diff updates the cell values of the raster with difference
+// of this raster and the values from the gien eval function.
+// The data will 4x over-sampled.
 func (r *Raster) Diff(eval func(float64, float64) (float64, bool)) {
 	var wg sync.WaitGroup
 
@@ -181,6 +191,9 @@
 	wg.Wait()
 }
 
+// ZExtent returns the z-range of the raster.
+// The last return value is false if the raster
+// only consists of no data values.
 func (r *Raster) ZExtent() (float64, float64, bool) {
 	min, max := math.MaxFloat64, -math.MaxFloat64
 	for _, v := range r.Cells {
@@ -197,6 +210,8 @@
 	return min, max, min != math.MaxFloat64
 }
 
+// Trace generates contour lines of this raster given
+// the given class breaks.
 func (r *Raster) Trace(heights ClassBreaks) []wkb.MultiPolygonGeom {
 	start := time.Now()