add support for .tif.ovr external overviews (#6)

README.md

@@ -35,12 +35,22 @@ go install github.com/airbusgeo/cogger/cmd/cogger@latest
 
 ### Binary
 
+#### With internal overviews
+
 ```bash
 gdal_translate -of GTIFF -co BIGTIFF=YES -co TILED=YES -co COMPRESS=ZSTD -co NUM_THREADS=4 input.file geotif.tif
-gdaladdo --config GDAL_NUM_THREADS 4 geotif.tif 2 4 8 16 32
+gdaladdo --config GDAL_NUM_THREADS 4 --config COMPRESS_OVERVIEW ZSTD geotif.tif 2 4 8 16 32
 cogger -output mycog.tif geotif.tif
 ```
 
+#### With external overviews
+
+```bash
+gdal_translate -of GTIFF -co BIGTIFF=YES -co TILED=YES -co COMPRESS=ZSTD -co NUM_THREADS=4 input.file geotif.tif
+gdaladdo -ro --config GDAL_NUM_THREADS 4 --config COMPRESS_OVERVIEW ZSTD geotif.tif 2 4 8 16 32 #creates geotif.tif.ovr
+cogger -output mycog.tif geotif.tif geotif.tif.ovr
+```
+
 ### Library
 
 The cogger API consists of a single function:

cogger_test.go

@@ -6,36 +6,41 @@ import (
 	"io"
 	"os"
 	"testing"
+
+	"github.com/google/tiff"
 )
 
-func testCase(t *testing.T, filename string) {
+func testCase(t *testing.T, expected_filename string, filenames ...string) {
 	t.Helper()
-	f, err := os.Open("testdata/cog_" + filename)
+	f, err := os.Open("testdata/" + expected_filename)
 	if err != nil {
 		t.Fatal(err)
 	}
 	hasher := md5.New()
 	_, _ = io.Copy(hasher, f)
 	srchash := hasher.Sum(nil)
 	f.Close()
-	f, err = os.Open("testdata/" + filename)
-	if err != nil {
-		t.Fatal(err)
-	}
-	defer f.Close()
 
-	_, _ = f.Seek(0, io.SeekStart)
+	files := make([]tiff.ReadAtReadSeeker, len(filenames))
+	for i := range filenames {
+		f, err = os.Open("testdata/" + filenames[i])
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer f.Close()
+		files[i] = f
+	}
 
 	buf := bytes.Buffer{}
 
 	hasher.Reset()
-	_ = Rewrite(&buf, f)
+	_ = Rewrite(&buf, files...)
 	_, _ = io.Copy(hasher, &buf)
 
 	coghash := hasher.Sum(nil)
 
 	if !bytes.Equal(coghash, srchash) {
-		t.Errorf("mismatch on %s: %x / %x", filename, srchash, coghash)
+		t.Errorf("mismatch on %v: %x / %x", filenames, srchash, coghash)
 	}
 }
 
@@ -49,6 +54,11 @@ func TestCases(t *testing.T) {
 		"rgb.tif",
 	}
 	for i := range cases {
-		testCase(t, cases[i])
+		testCase(t, "cog_"+cases[i], cases[i])
 	}
 }
+
+func TestMultiFiles(t *testing.T) {
+	testCase(t, "cog_ext_ovr.tif", "exttest.tif", "exttest.tif.ovr")
+	testCase(t, "cog_ext_multi.tif", "exttest.tif", "exttest.tif.2", "exttest.tif.4")
+}

loader.go

@@ -8,8 +8,7 @@ import (
 	"github.com/google/tiff"
 )
 
-func loadMultipleTIFFs(tifs []tiff.TIFF) (*cog, error) {
-	cog := new()
+func loadMultipleTIFFs(tifs []tiff.TIFF) ([]*ifd, error) {
 	ifds := make([]*ifd, 0)
 	for it, tif := range tifs {
 		tifds := tif.IFDs()
@@ -18,41 +17,22 @@ func loadMultipleTIFFs(tifs []tiff.TIFF) (*cog, error) {
 			if err != nil {
 				return nil, err
 			}
-			if ifd.SubfileType&subfileTypeReducedImage == subfileTypeReducedImage {
-				return nil, fmt.Errorf("cannot load multiple tifs if they contain overviews")
-			}
 			if it != 0 {
+				//check that the additional files are smaller than the first, i.e. that they represent an overview
+				if ifd.ImageLength >= ifds[0].ImageLength || ifd.ImageWidth >= ifds[0].ImageWidth {
+					return nil, fmt.Errorf("provided tiff %d size %dx%d is larger than first tiff size %dx%d. when using multiple files, the subsequent ones must be overviews of the first one",
+						it, ifd.ImageWidth, ifd.ImageLength, ifds[0].ImageWidth, ifds[0].ImageLength)
+				}
+				//force to overview
 				ifd.SubfileType |= subfileTypeReducedImage
 			}
 			ifds = append(ifds, ifd)
 		}
 	}
-	sort.Slice(ifds, func(i, j int) bool {
-		//return in order: fullres, fullresmasks, ovr1, ovr1masks, ovr2, ....
-		if ifds[i].ImageLength != ifds[j].ImageLength {
-			return ifds[i].ImageLength > ifds[j].ImageLength
-		}
-		return ifds[i].SubfileType < ifds[j].SubfileType
-	})
-	if ifds[0].SubfileType != 0 {
-		return nil, fmt.Errorf("failed sort: first px=%d type=%d", ifds[0].ImageLength, ifds[0].SubfileType)
-	}
-	cog.ifd = ifds[0]
-	curOvr := cog.ifd
-	l := curOvr.ImageLength
-	for _, ci := range ifds[1:] {
-		if ci.ImageLength == l {
-			curOvr.AddMask(ci)
-		} else {
-			curOvr.AddOverview(ci)
-			curOvr = ci
-			l = curOvr.ImageLength
-		}
-	}
-	return cog, nil
+	return ifds, nil
 }
-func loadSingleTIFF(tif tiff.TIFF) (*cog, error) {
-	cog := new()
+
+func loadSingleTIFF(tif tiff.TIFF) ([]*ifd, error) {
 	tifds := tif.IFDs()
 	ifds := make([]*ifd, len(tifds))
 	var err error
@@ -62,29 +42,7 @@ func loadSingleTIFF(tif tiff.TIFF) (*cog, error) {
 			return nil, err
 		}
 	}
-	sort.Slice(ifds, func(i, j int) bool {
-		//return in order: fullres, fullresmasks, ovr1, ovr1masks, ovr2, ....
-		if ifds[i].ImageLength != ifds[j].ImageLength {
-			return ifds[i].ImageLength > ifds[j].ImageLength
-		}
-		return ifds[i].SubfileType < ifds[j].SubfileType
-	})
-	if ifds[0].SubfileType != 0 {
-		return nil, fmt.Errorf("failed sort: first px=%d type=%d", ifds[0].ImageLength, ifds[0].SubfileType)
-	}
-	cog.ifd = ifds[0]
-	curOvr := cog.ifd
-	l := curOvr.ImageLength
-	for _, ci := range ifds[1:] {
-		if ci.ImageLength == l {
-			curOvr.AddMask(ci)
-		} else {
-			curOvr.AddOverview(ci)
-			curOvr = ci
-			l = curOvr.ImageLength
-		}
-	}
-	return cog, nil
+	return ifds, nil
 }
 
 func loadIFD(r tiff.BReader, tifd tiff.IFD) (*ifd, error) {
@@ -121,18 +79,45 @@ func Rewrite(out io.Writer, readers ...tiff.ReadAtReadSeeker) error {
 	if err != nil {
 		return fmt.Errorf("consistency check: %w", err)
 	}
-	var cog *cog
+	var ifds []*ifd
 	if len(tiffs) > 1 {
-		cog, err = loadMultipleTIFFs(tiffs)
+		ifds, err = loadMultipleTIFFs(tiffs)
 		if err != nil {
 			return fmt.Errorf("load: %w", err)
 		}
 	} else {
-		cog, err = loadSingleTIFF(tiffs[0])
+		ifds, err = loadSingleTIFF(tiffs[0])
 		if err != nil {
 			return fmt.Errorf("load: %w", err)
 		}
 	}
+	sort.Slice(ifds, func(i, j int) bool {
+		//return in order: fullres, fullresmasks, ovr1, ovr1masks, ovr2, ....
+		if ifds[i].ImageLength != ifds[j].ImageLength {
+			return ifds[i].ImageLength > ifds[j].ImageLength
+		}
+		return ifds[i].SubfileType < ifds[j].SubfileType
+	})
+	if ifds[0].SubfileType != 0 {
+		return fmt.Errorf("failed sort: first px=%d type=%d", ifds[0].ImageLength, ifds[0].SubfileType)
+	}
+	cog := new()
+	cog.ifd = ifds[0]
+	curOvr := cog.ifd
+	l := curOvr.ImageLength
+	for _, ci := range ifds[1:] {
+		if ci.ImageLength == l {
+			err = curOvr.AddMask(ci)
+			if err != nil {
+				return err
+			}
+		} else {
+			curOvr.AddOverview(ci)
+			curOvr = ci
+			l = curOvr.ImageLength
+		}
+	}
+
 	err = cog.write(out)
 	if err != nil {
 		return fmt.Errorf("mucog write: %w", err)