Second checkpoint

internal/raster/gdal.go

@@ -0,0 +1,58 @@
+// Package raster converts rasters to Cloud-Optimized GeoTIFFs and reads their
+// footprints using the GDAL command-line tools (gdal_translate, gdalinfo),
+// which must be installed in the worker environment.
+package raster
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"os/exec"
+	"strings"
+)
+
+// GDALConverter shells out to GDAL.
+type GDALConverter struct {
+	compression string
+}
+
+// NewGDALConverter returns a converter using DEFLATE compression.
+func NewGDALConverter() *GDALConverter {
+	return &GDALConverter{compression: "DEFLATE"}
+}
+
+// ToCOG converts the source raster to a Cloud-Optimized GeoTIFF at dst. The COG
+// driver builds internal tiling and overviews.
+func (c *GDALConverter) ToCOG(ctx context.Context, src, dst string) error {
+	cmd := exec.CommandContext(ctx, "gdal_translate",
+		"-of", "COG",
+		"-co", "COMPRESS="+c.compression,
+		src, dst,
+	)
+	var stderr strings.Builder
+	cmd.Stderr = &stderr
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("gdal_translate: %w: %s", err, strings.TrimSpace(stderr.String()))
+	}
+	return nil
+}
+
+// Footprint returns the raster's footprint as a GeoJSON polygon in EPSG:4326, or
+// nil if the raster has no spatial reference.
+func (c *GDALConverter) Footprint(ctx context.Context, src string) ([]byte, error) {
+	out, err := exec.CommandContext(ctx, "gdalinfo", "-json", src).Output()
+	if err != nil {
+		return nil, fmt.Errorf("gdalinfo: %w", err)
+	}
+
+	var info struct {
+		Wgs84Extent json.RawMessage `json:"wgs84Extent"`
+	}
+	if err := json.Unmarshal(out, &info); err != nil {
+		return nil, fmt.Errorf("parse gdalinfo: %w", err)
+	}
+	if len(info.Wgs84Extent) == 0 || string(info.Wgs84Extent) == "null" {
+		return nil, nil
+	}
+	return info.Wgs84Extent, nil
+}