Merge pull request #454 from geotiffjs/feat-ifd-improvements

feat: keep a separate map of tag IDs to parsed IFD values in `ImageFileDescriptor` object

Author: constantinius

package.json

@@ -143,7 +143,7 @@
     "lint:fix": "npm run lint -- --fix",
     "prepare": "npm run build",
     "pretest": "npm run lint",
-    "test": "mocha --full-trace test/geotiff.spec.js"
+    "test": "mocha --full-trace test/*.spec.js"
   },
   "author": "Fabian Schindler",
   "browser": {

src/geotiff.js

@@ -175,12 +175,20 @@ function getValues(dataSlice, fieldType, count, offset) {
 }
 
 /**
- * Data class to store the parsed file directory, geo key directory and
+ * Data class to store the parsed file directory (+ its raw form), geo key directory and
  * offset to the next IFD
  */
 class ImageFileDirectory {
-  constructor(fileDirectory, geoKeyDirectory, nextIFDByteOffset) {
+  /**
+   * Create an ImageFileDirectory.
+   * @param {object} fileDirectory the file directory, mapping tag names to values
+   * @param {Map} rawFileDirectory the raw file directory, mapping tag IDs to values
+   * @param {object} geoKeyDirectory the geo key directory, mapping geo key names to values
+   * @param {number} nextIFDByteOffset the byte offset to the next IFD
+   */
+  constructor(fileDirectory, rawFileDirectory, geoKeyDirectory, nextIFDByteOffset) {
     this.fileDirectory = fileDirectory;
+    this.rawFileDirectory = rawFileDirectory;
     this.geoKeyDirectory = geoKeyDirectory;
     this.nextIFDByteOffset = nextIFDByteOffset;
   }
@@ -372,6 +380,7 @@ class GeoTIFF extends GeoTIFFBase {
     }
 
     const fileDirectory = {};
+    const rawFileDirectory = new Map();
 
     // loop over the IFD and create a file directory object
     let i = offset + (this.bigTiff ? 8 : 2);
@@ -414,8 +423,12 @@ class GeoTIFF extends GeoTIFFBase {
         value = fieldValues;
       }
 
-      // write the tags value to the file directly
-      fileDirectory[fieldTagNames[fieldTag]] = value;
+      // write the tags value to the file directory
+      const tagName = fieldTagNames[fieldTag];
+      if (tagName) {
+        fileDirectory[tagName] = value;
+      }
+      rawFileDirectory.set(fieldTag, value);
     }
     const geoKeyDirectory = parseGeoKeyDirectory(fileDirectory);
     const nextIFDByteOffset = dataSlice.readOffset(
@@ -424,6 +437,7 @@ class GeoTIFF extends GeoTIFFBase {
 
     return new ImageFileDirectory(
       fileDirectory,
+      rawFileDirectory,
       geoKeyDirectory,
       nextIFDByteOffset,
     );

src/globals.js

@@ -213,6 +213,25 @@ for (const key in fieldTypeNames) {
   }
 }
 
+/**
+ * Registers a new field tag
+ * @param {number} tag the numeric tiff tag
+ * @param {string} name the name of the tag that will be reported in the IFD
+ * @param {number} type the tags data type
+ * @param {Boolean} isArray whether the tag is an array
+ */
+export function registerTag(tag, name, type = undefined, isArray = false) {
+  fieldTags[name] = tag;
+  fieldTagNames[tag] = name;
+
+  if (type) {
+    fieldTypes[name] = type;
+  }
+  if (isArray) {
+    arrayFields.push(tag);
+  }
+}
+
 export const photometricInterpretations = {
   WhiteIsZero: 0,
   BlackIsZero: 1,

test/globals.spec.js

@@ -0,0 +1,35 @@
+/* eslint-disable global-require, no-unused-expressions */
+import { expect } from 'chai';
+
+import { registerTag, fieldTags, fieldTagNames, fieldTypes, arrayFields } from '../src/globals.js';
+
+describe('registerTag()', () => {
+  it('shall register simple tags', () => {
+    registerTag(0xBEA1, 'TestTag');
+    expect(fieldTags).to.have.property('TestTag');
+    expect(fieldTagNames).to.have.property(String(0xBEA1));
+    expect(fieldTypes).to.not.have.property('TestTag');
+    expect(arrayFields).to.not.include(0xBEA1);
+  });
+  it('shall register tags with type', () => {
+    registerTag(0xBEA2, 'TestTagRational', 'RATIONAL');
+    expect(fieldTags).to.have.property('TestTagRational');
+    expect(fieldTagNames).to.have.property(String(0xBEA2));
+    expect(fieldTypes).to.have.property('TestTagRational');
+    expect(arrayFields).to.not.include(0xBEA1);
+  });
+  it('shall register array tags', () => {
+    registerTag(0xBEA3, 'TestTagArray', undefined, true);
+    expect(fieldTags).to.have.property('TestTagArray');
+    expect(fieldTagNames).to.have.property(String(0xBEA3));
+    expect(fieldTypes).to.not.have.property('TestTagArray');
+    expect(arrayFields).to.include(0xBEA3);
+  });
+  it('shall register typed array tags', () => {
+    registerTag(0xBEA4, 'TestTagArrayTyped', 'LONG', true);
+    expect(fieldTags).to.have.property('TestTagArrayTyped');
+    expect(fieldTagNames).to.have.property(String(0xBEA4));
+    expect(fieldTypes).to.have.property('TestTagArrayTyped');
+    expect(arrayFields).to.include(0xBEA4);
+  });
+});