From fc21a30d6754f37923b92ee4fe26c557ff6d9378 Mon Sep 17 00:00:00 2001
From: Blayne Chard <blayne@chard.com>
Date: Sun, 26 Nov 2023 17:33:12 +1300
Subject: [PATCH] feat: expose gdal's NO_DATA as a getter on the image (#1230)

---
 packages/core/src/__test__/cog.read.test.ts |  3 +++
 packages/core/src/tiff.image.ts             | 13 +++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/packages/core/src/__test__/cog.read.test.ts b/packages/core/src/__test__/cog.read.test.ts
index ac6ec337..e1c8a133 100644
--- a/packages/core/src/__test__/cog.read.test.ts
+++ b/packages/core/src/__test__/cog.read.test.ts
@@ -86,6 +86,9 @@ describe('CogRead', () => {
     assert.equal(im.value(TiffTag.SampleFormat), SampleFormat.Float);
     assert.equal(im.value(TiffTag.Photometric), Photometric.MinIsBlack);
 
+    assert.equal(im.value(TiffTag.GdalNoData), '-9999');
+    assert.equal(im.noData, -9999);
+
     assert.equal(im.tagsGeo.get(TiffTagGeo.GTCitationGeoKey), 'NZGD2000 / New Zealand Transverse Mercator 2000');
     assert.equal(im.tagsGeo.get(TiffTagGeo.GeodeticCitationGeoKey), 'NZGD2000');
     assert.deepEqual(await im.fetch(TiffTag.StripByteCounts), [8064, 8064, 8064, 8064, 8064, 8064, 8064, 5040]);
diff --git a/packages/core/src/tiff.image.ts b/packages/core/src/tiff.image.ts
index 67737744..3663d1fd 100644
--- a/packages/core/src/tiff.image.ts
+++ b/packages/core/src/tiff.image.ts
@@ -162,6 +162,19 @@ export class TiffImage {
     return this.tagsGeo.get(tag) as TiffTagGeoType[T];
   }
 
+  /**
+   * Load and parse the GDAL_NODATA Tifftag
+   *
+   * @throws if the tag is not loaded
+   * @returns null if the tag does not exist
+   */
+  get noData(): number | null {
+    const tag = this.tags.get(TiffTag.GdalNoData);
+    if (tag == null) return null;
+    if (tag.value) return Number(tag.value);
+    throw new Error('GdalNoData tag is not loaded');
+  }
+
   /**
    * Load and unpack the GeoKeyDirectory
    *