From 1552153a2fde15d5a6adcf465ef347f106cacc22 Mon Sep 17 00:00:00 2001
From: Thomas Bonfort <thomas.bonfort@airbus.com>
Date: Mon, 28 Jun 2021 18:35:52 +0200
Subject: [PATCH 1/4] add support for .tif.ovr external overviews

---
 cogger_test.go             |  32 ++++++++-----
 loader.go                  |  94 +++++++++++++++----------------------
 testdata/cog_ext_multi.tif | Bin 0 -> 4797 bytes
 testdata/cog_ext_ovr.tif   | Bin 0 -> 4797 bytes
 testdata/exttest.tif       | Bin 0 -> 2393 bytes
 testdata/exttest.tif.2     | Bin 0 -> 1299 bytes
 testdata/exttest.tif.4     | Bin 0 -> 889 bytes
 testdata/exttest.tif.ovr   | Bin 0 -> 2204 bytes
 8 files changed, 59 insertions(+), 67 deletions(-)
 create mode 100644 testdata/cog_ext_multi.tif
 create mode 100644 testdata/cog_ext_ovr.tif
 create mode 100644 testdata/exttest.tif
 create mode 100644 testdata/exttest.tif.2
 create mode 100644 testdata/exttest.tif.4
 create mode 100644 testdata/exttest.tif.ovr

diff --git a/cogger_test.go b/cogger_test.go
index d9eb19a..4977297 100644
--- a/cogger_test.go
+++ b/cogger_test.go
@@ -6,11 +6,13 @@ 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)
 	}
@@ -18,24 +20,27 @@ func testCase(t *testing.T, filename string) {
 	_, _ = 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")
+}
diff --git a/loader.go b/loader.go
index 5f759f2..98ac205 100644
--- a/loader.go
+++ b/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 +79,42 @@ 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 {
+			curOvr.AddMask(ci)
+		} else {
+			curOvr.AddOverview(ci)
+			curOvr = ci
+			l = curOvr.ImageLength
+		}
+	}
+
 	err = cog.write(out)
 	if err != nil {
 		return fmt.Errorf("mucog write: %w", err)
diff --git a/testdata/cog_ext_multi.tif b/testdata/cog_ext_multi.tif
new file mode 100644
index 0000000000000000000000000000000000000000..a36c8f4cd67c6f853c52465318379fd0b0e68e6c
GIT binary patch
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diff --git a/testdata/cog_ext_ovr.tif b/testdata/cog_ext_ovr.tif
new file mode 100644
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GIT binary patch
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From 428b53e565eb1037063599e41a2f2fd27a1acd7c Mon Sep 17 00:00:00 2001
From: Thomas Bonfort <thomas.bonfort@airbus.com>
Date: Mon, 28 Jun 2021 18:42:37 +0200
Subject: [PATCH 2/4] add missing error check

---
 loader.go | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/loader.go b/loader.go
index 98ac205..8a9c06d 100644
--- a/loader.go
+++ b/loader.go
@@ -107,7 +107,10 @@ func Rewrite(out io.Writer, readers ...tiff.ReadAtReadSeeker) error {
 	l := curOvr.ImageLength
 	for _, ci := range ifds[1:] {
 		if ci.ImageLength == l {
-			curOvr.AddMask(ci)
+			err = curOvr.AddMask(ci)
+			if err != nil {
+				return err
+			}
 		} else {
 			curOvr.AddOverview(ci)
 			curOvr = ci

From 1c24b61c9779f3000c36f747a72ae0286889128c Mon Sep 17 00:00:00 2001
From: Thomas Bonfort <thomas.bonfort@airbus.com>
Date: Mon, 28 Jun 2021 18:46:05 +0200
Subject: [PATCH 3/4] fixup readme

---
 README.md | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/README.md b/README.md
index 98a75f9..448f18e 100644
--- a/README.md
+++ b/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
 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 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:

From 06b078f7629fdfe1759d5c309505ca44b8eccb35 Mon Sep 17 00:00:00 2001
From: Thomas Bonfort <thomas.bonfort@airbus.com>
Date: Mon, 28 Jun 2021 19:03:50 +0200
Subject: [PATCH 4/4] fixup readme

---
 README.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index 448f18e..fea84cb 100644
--- a/README.md
+++ b/README.md
@@ -39,7 +39,7 @@ go install github.com/airbusgeo/cogger/cmd/cogger@latest
 
 ```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
 ```
 
@@ -47,7 +47,7 @@ cogger -output mycog.tif geotif.tif
 
 ```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 geotif.tif 2 4 8 16 32 #creates geotif.tif.ovr
+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
 ```