Fixes #14. mtseeder and mtwebmapper now have command line flags -ymin=block and -ymax=block to limit the y range of mapping. Defaults to full range.

common/basetilecreator.go

@@ -18,10 +18,15 @@ const (
 	yOrderCapacity = 512
 )
 
+const (
+	MaxHeight = 1934
+	MinHeight = -1934
+)
+
 // To scan the whole height in terms of the y coordinate
 // the database is queried in height units defined in the tileDepths table.
 var tileDepths = [...][2]int16{
-	{1024, 1934},
+	{1024, MaxHeight},
 	{256, 1023},
 	{128, 255},
 	{64, 127},
@@ -40,7 +45,7 @@ var tileDepths = [...][2]int16{
 	{-128, -65},
 	{-256, -129},
 	{-1024, -257},
-	{-1934, -1025}}
+	{MinHeight, -1025}}
 
 var BackgroundColor = color.RGBA{R: 0xff, G: 0xff, B: 0xff, A: 0xff}
 
@@ -49,6 +54,8 @@ type BaseTileCreator struct {
 	colors     *Colors
 	renderer   *Renderer
 	yOrder     *YOrder
+	yMin       int16
+	yMax       int16
 	baseDir    string
 	update     bool
 	emptyImage []byte
@@ -57,15 +64,19 @@ type BaseTileCreator struct {
 func NewBaseTileCreator(
 	client *RedisClient,
 	colors *Colors,
+	yMin, yMax int16,
 	transparent bool,
 	baseDir string,
 	update bool) *BaseTileCreator {
 	renderer := NewRenderer(tileWidth, tileHeight, transparent)
+	yMin, yMax = Order16(yMin, yMax)
 	return &BaseTileCreator{
 		client:   client,
 		colors:   colors,
 		renderer: renderer,
 		yOrder:   NewYOrder(renderer, yOrderCapacity),
+		yMin:     yMin,
+		yMax:     yMax,
 		baseDir:  baseDir,
 		update:   update}
 }
@@ -95,8 +106,11 @@ func (btc *BaseTileCreator) CreateTile(x, z int16, i, j int) error {
 		X2: int16(tileWidth) - 1, Z2: int16(tileHeight) - 1}
 
 	for _, yRange := range tileDepths {
-		c1.Y = yRange[0]
-		c2.Y = yRange[1]
+		if yRange[0] > btc.yMax || yRange[1] < btc.yMin {
+			continue
+		}
+		c1.Y = max16(yRange[0], btc.yMin)
+		c2.Y = min16(yRange[1], btc.yMax)
 
 		nareas = btc.renderer.UncoveredAreas(nareas, oareas)
 

common/math.go

@@ -63,6 +63,20 @@ func Clamp32f(x, a, b float32) float32 {
 	return x
 }
 
+func Order(a, b int) (int, int) {
+	if a < b {
+		return a, b
+	}
+	return b, a
+}
+
+func Order16(a, b int16) (int16, int16) {
+	if a < b {
+		return a, b
+	}
+	return b, a
+}
+
 func Order64(a, b int64) (int64, int64) {
 	if a < b {
 		return a, b