Got the basics of the snap program working.

cmd/snap/README.md

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+# Raster
+Raster is a raster tile server that takes a mapbox style files and generates raster tiles for it.
+
+
+# URLs that are supported by the application.
+
+
+
+## Raster Tile Server API
+
+```
+/styles/${style-name:string}/tiles/[${tilesize:int}/]${z:int}/${x:int}/${y:int}[@2x][.${file-extention:enum(jpg,png)}]
+```
+
+* style-name     [required] : the name of the style. If loaded via the command line the style name will be "default" (currently this 
+the only thing that is supported.) 
+* tilesize       [optional] : Default is 512, valid valus are positive multiples of 256. 
+* z              [required] : the zoom
+* x              [required] : the x coordinate (column) in the slippy tile scheme.
+* y              [required] : the y coordinate (row) in the slippy tile scheme.
+* @2x            [optional] : to serve hight definition (retina) tiles. Omit to serve standard definition tiles.
+* file-extension [optional] : the file type to encode the raster image in. Currently supported formats png, jpg. Default is jpg.
+
+## Static map server
+For generating an image of a map at a given point and zoom use the following url.
+
+```
+/styles/${style-name:string}/static/${lon:float},${lat:float},${zoom:float},[${bearing:float],[${pitch:float}]]/${width:int}x${height:int}[@2x][.${file-extention:enum(jpg,png)}]
+```
+
+* style-name     [required] : the name of the style. If loaded via the command line the style name will be "default" (currently this 
+the only thing that is supported.) 
+* lon       [optional] : Default is 512, valid valus are positive multiples of 256. 
+* lat       [required] : the zoom
+* zoom      [required] : the x coordinate (column) in the slippy tile scheme.
+* bearing   [required] : the y coordinate (row) in the slippy tile scheme.
+* @2x            [optional] : to serve hight definition (retina) tiles. Omit to serve standard definition tiles.
+* file-extension [optional] : the file type to encode the raster image in. Currently supported formats png, jpg. Default is jpg.
+
+## Health check
+
+If the server is up this url will return a 200.
+
+```
+/health
+```
+
+
+

cmd/snap/cmd/generate.go

@@ -0,0 +1,101 @@
+package cmd
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+
+	"github.com/spf13/cobra"
+)
+
+var cmdGenerateWidth int
+var cmdGenerateHeight int
+var cmdGeneratePPIRatio float64
+var cmdGeneratePitch float64
+var cmdGenerateBearing float64
+var cmdGenerateFormat string
+
+var cmdGenerate = &cobra.Command{
+	Use:     "generate",
+	Short:   "generate an image for given map coordinates.",
+	Aliases: []string{"gen"},
+}
+
+func ValidateGenerateParams() error {
+	if cmdGenerateWidth < 1 {
+		return errors.New("--width must be greater then or equal to 1")
+	}
+	if cmdGenerateHeight < 1 {
+		return errors.New("--height must be greater then or equal to 1")
+	}
+	if cmdGeneratePitch < 0 {
+		return errors.New("--pitch must be greater then or equal to 0")
+	}
+	if cmdGenerateBearing < 0 {
+		return errors.New("--bearing must be greater then or equal to 0")
+	}
+	cmdGenerateFormat = strings.ToLower(cmdGenerateFormat)
+	if cmdGenerateFormat != "" && (cmdGenerateFormat != "jpg" || cmdGenerateFormat != "png") {
+		return errors.New("--format must be jpg or png")
+	}
+	return nil
+
+}
+
+func IsValidLngString(lng string) bool {
+
+	f64, err := strconv.ParseFloat(strings.TrimSpace(lng), 64)
+	if err != nil {
+		return false
+	}
+	return -180.0 <= f64 && f64 <= 190.0
+}
+
+func IsValidLatString(lat string) bool {
+
+	f64, err := strconv.ParseFloat(strings.TrimSpace(lat), 64)
+	if err != nil {
+		return false
+	}
+	return -90.0 <= f64 && f64 <= 90.0
+}
+
+func genImage(center [2]float64, zoom float64, output string) error {
+	ext, err := getFormatString(output)
+	if err != nil {
+		return err
+	}
+	var out io.Writer
+
+	if output == "" {
+		out = os.Stdout
+	} else {
+		file, err := os.Create(output)
+		if err != nil {
+			return fmt.Errorf("error creating output file: %v -- %v\n", output, err)
+		}
+		defer file.Close()
+		out = file
+	}
+
+	if _, err := generateZoomCenterImage(out, RootStyle, cmdGenerateWidth, cmdGenerateHeight, cmdGeneratePPIRatio, cmdGeneratePitch, cmdGenerateBearing, center, zoom, ext); err != nil {
+		return fmt.Errorf("failed to generate image: %v", err)
+	}
+	return nil
+}
+
+func init() {
+	pf := cmdGenerate.PersistentFlags()
+	pf.IntVar(&cmdGenerateWidth, "width", 512, "Width of the image to generate.")
+	pf.IntVar(&cmdGenerateHeight, "height", 512, "Height of the image to generate.")
+	pf.Float64Var(&cmdGeneratePPIRatio, "ppiratio", 1.0, "The pixel per inch ratio.")
+	pf.Float64Var(&cmdGeneratePitch, "pitch", 0.0, "The pitch of the map.")
+	pf.Float64Var(&cmdGenerateBearing, "bearing", 0.0, "The bearing of the map.")
+	pf.StringVar(&cmdGenerateFormat, "format", "", "Defaults to the ext of the output file, or jpg if not provided.")
+
+	cmdGenerate.AddCommand(cmdGenerateBounds)
+	cmdGenerate.AddCommand(cmdGenerateCenter)
+}

cmd/snap/cmd/generate_bounds.go

@@ -0,0 +1,67 @@
+package cmd
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+
+	"github.com/go-spatial/geom/spherical"
+	"github.com/go-spatial/go-mbgl/internal/bounds"
+	mbgl "github.com/go-spatial/go-mbgl/mbgl/simplified"
+	"github.com/spf13/cobra"
+)
+
+var cmdGenerateBounds = &cobra.Command{
+	Use:   "bounds lng lat lng lat [output_file.jpg]",
+	Short: "generate image using bounds",
+	Long:  `use a bounds described as (lng lat lng lat) set of coordinates to generate the image.`,
+	Args: func(cmd *cobra.Command, args []string) error {
+		if len(args) < 4 {
+			return errors.New("requres at bounds( lng lat lng lat )")
+		}
+		if len(args) > 5 {
+			return errors.New("extra values provided")
+		}
+		if !IsValidLngString(args[0]) {
+			return fmt.Errorf("Longitude must be between -180.0 and 180.0 : given %v", args[0])
+		}
+		if !IsValidLatString(args[1]) {
+			return fmt.Errorf("Latitude must be between -90.0 and 90.0 : given %v", args[1])
+		}
+		if !IsValidLngString(args[2]) {
+			return fmt.Errorf("Longitude must be between -180.0 and 80.0 : given %v", args[2])
+		}
+		if !IsValidLatString(args[3]) {
+			return fmt.Errorf("Latitude must be between -90.0 and 90.0 : given %v", args[3])
+		}
+		return nil
+	},
+	Run: commandGenerateBounds,
+}
+
+func commandGenerateBounds(cmd *cobra.Command, args []string) {
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	mbgl.StartSnapshotManager(ctx)
+
+	// Already checked in the Args validation function
+	lng1, _ := strconv.ParseFloat(strings.TrimSpace(args[0]), 64)
+	lat1, _ := strconv.ParseFloat(strings.TrimSpace(args[1]), 64)
+	lng2, _ := strconv.ParseFloat(strings.TrimSpace(args[2]), 64)
+	lat2, _ := strconv.ParseFloat(strings.TrimSpace(args[3]), 64)
+	hull := spherical.Hull([2]float64{lat1, lng1}, [2]float64{lat2, lng2})
+	center, zoom := bounds.CenterZoom(hull, float64(cmdGenerateWidth), float64(cmdGenerateHeight))
+	output := ""
+	if len(args) == 5 {
+		output = args[4]
+	}
+	if err := genImage(center, zoom, output); err != nil {
+		fmt.Fprintf(os.Stderr, err.Error())
+		os.Exit(1)
+	}
+}

cmd/snap/cmd/generate_center.go

@@ -0,0 +1,77 @@
+package cmd
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+
+	mbgl "github.com/go-spatial/go-mbgl/mbgl/simplified"
+	"github.com/spf13/cobra"
+)
+
+var cmdGenerateCenter = &cobra.Command{
+	Use:   "center lng lat zoom [output_file.jpg]",
+	Short: "generate image using center and zoom",
+	Long:  `use a center point (lng lat) and a zoom to generate the image.`,
+	Args: func(cmd *cobra.Command, args []string) error {
+		if len(args) < 3 {
+			return errors.New("requres a center (lng lat) and a zoom.")
+		}
+		if len(args) > 4 {
+			return errors.New("extra values provided")
+		}
+		if !IsValidLngString(args[0]) {
+			return fmt.Errorf("Longitude must be between -180.0 and 180.0 : given %v", args[0])
+		}
+		if !IsValidLatString(args[1]) {
+			return fmt.Errorf("Latitude must be between -90.0 and 90.0 : given %v", args[1])
+		}
+		z64, err := strconv.ParseFloat(strings.TrimSpace(args[2]), 64)
+		if err != nil || z64 < 0 || z64 > 22 {
+			return fmt.Errorf("zoom (%v) must be a number from 0 - 22", args[2])
+		}
+
+		return nil
+	},
+	Run: commandGenerateCenter,
+}
+
+func getFormatString(file string) (ext string, err error) {
+	if cmdGenerateFormat != "" {
+		ext = cmdGenerateFormat
+	} else {
+		ext = strings.ToLower(strings.TrimPrefix(filepath.Ext(file), "."))
+		if ext == "" {
+			ext = "jpg"
+		} else if ext != "jpg" && ext != "png" {
+			return "jpg", fmt.Errorf("output format(%v) must be jpg or png", ext)
+		}
+	}
+	return ext, nil
+}
+
+func commandGenerateCenter(cmd *cobra.Command, args []string) {
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	mbgl.StartSnapshotManager(ctx)
+
+	// Already checked in the Args validation function
+	lng, _ := strconv.ParseFloat(strings.TrimSpace(args[0]), 64)
+	lat, _ := strconv.ParseFloat(strings.TrimSpace(args[1]), 64)
+	zoom, _ := strconv.ParseFloat(strings.TrimSpace(args[2]), 64)
+
+	output := ""
+	if len(args) == 4 {
+		output = args[3]
+	}
+	if err := genImage([2]float64{lng, lat}, zoom, output); err != nil {
+		fmt.Fprintf(os.Stderr, err.Error())
+		os.Exit(1)
+	}
+}

cmd/snap/cmd/root.go

@@ -0,0 +1,22 @@
+package cmd
+
+import "github.com/spf13/cobra"
+
+var RootCmd = &cobra.Command{
+	Use:   "snap",
+	Short: "snap is a raster tile server",
+	Long:  `snap is a raster tile server version: ` + Version,
+}
+
+const DefaultRootStyle = "https://raw.githubusercontent.com/go-spatial/tegola-web-demo/master/styles/hot-osm.json"
+
+var RootStyle string = DefaultRootStyle
+
+func init() {
+
+	RootCmd.PersistentFlags().StringVarP(&RootStyle, "style", "s", DefaultRootStyle, "style to use. Style name will be default")
+
+	RootCmd.AddCommand(cmdServer)
+	RootCmd.AddCommand(cmdVersion)
+	RootCmd.AddCommand(cmdGenerate)
+}