GeoTiff tags weren't being saved out until I added the GeoTiff tags to Tiff_DirInfo.cs

[stewienj]

I tried to create a Tiff file with some GeoTiff tags, but the GeoTiff tags weren't being saved out.

This was fixed by adding the following TiffFieldInfo objects to the tiffFieldInfo field in Tiff_DirInfo.cs, at the appropriate positions to maintain order:

new TiffFieldInfo(TiffTag.GEOTIFF_MODELPIXELSCALETAG, -3, -3, TiffType.DOUBLE, FieldBit.Custom, true, true, "GeoTiffModelPixelScale"),
new TiffFieldInfo(TiffTag.GEOTIFF_MODELTIEPOINTTAG, -3, -3, TiffType.DOUBLE, FieldBit.Custom, true, true, "GeoTiffModelTiePoint"),
new TiffFieldInfo(TiffTag.GEOTIFF_GEOKEYDIRECTORYTAG, -3, -3, TiffType.SHORT, FieldBit.Custom, true, true, "GeoTiffGeoKeyDirectory"),
new TiffFieldInfo(TiffTag.GEOTIFF_GEOASCIIPARAMSTAG, -3, -3, TiffType.ASCII, FieldBit.Custom, true, true, "GeoTiffGeoAsciiParams"),

Here's some sample code based on your Black and White sample for writing out a GeoTiff that should appear in the middle of Australia when loaded in a mapping program:

public record TiffTagDataType<DataType>(int TagId, DataType[] Data)
{
  public object[] AsObjectArray() => [TagId, Data];
}

public class TiffBlackAndWhiteWithGeo
{
  public static void Create(string fileName)
  {
    const int width = 32;
    const int height = 100;
    const int samplesPerPixel = 1;
    const int bitsPerSample = 8;

    var GEOTIFF_MODELPIXELSCALETAG = new TiffTagDataType<double>(
      // Size of data
      3,
      // East/West degrees per pixel, North/South degrees per pixel, 0
      [1.0/width, 1.0/height, 0.0]
    );

    var GEOTIFF_MODELTIEPOINTTAG = new TiffTagDataType<double>(
      // Size of data
      6,
      [
        // Just leave as zeros
        0.0, 0.0, 0.0,
        // West Edge, North Edge, 0.0
        135.0, -25.0, 0.0, 0.0
      ]
    );

    // This specifies what coordinate system we are using and some other meta data. Didn't look up all of it.
    // Note the data is in groups of 4
    var GEOTIFF_GEOKEYDIRECTORYTAG = new TiffTagDataType<ushort>(
      // Size of data
      32,
      [
        1, 1, 0, 7,
        1024, 0, 1, 2,
        1025, 0, 1, 1,
        2048, 0, 1, 4326,
        2049, 34737, 7, 0,
        2054, 0, 1, 9102,
        2057, 34736, 1, 1,
        2059, 34736, 1, 0
      ]
    );

    var GEOTIFF_GEOASCIIPARAMSTAG = new TiffTagDataType<byte>(
      // Size of data, which is 1 more than the data for some reason when adding ascii strings
      8,
      // The | character is converted to a zero later on
      "WGS 84|"u8.ToArray()
    );

    var GDAL_NODATA = new TiffTagDataType<byte>(
      // Size of data
      1,
      // A pixel value of zero means no data when we add a zero here
      [0]
    );

    using (Tiff output = Tiff.Open(fileName, "w"))
    {
      output.SetField(TiffTag.IMAGEWIDTH, width / samplesPerPixel);
      output.SetField(TiffTag.SAMPLESPERPIXEL, samplesPerPixel);
      output.SetField(TiffTag.BITSPERSAMPLE, bitsPerSample);
      output.SetField(TiffTag.ORIENTATION, Orientation.TOPLEFT);
      output.SetField(TiffTag.PLANARCONFIG, PlanarConfig.CONTIG);
      output.SetField(TiffTag.PHOTOMETRIC, Photometric.MINISBLACK);
      output.SetField(TiffTag.ROWSPERSTRIP, output.DefaultStripSize(0));

      output.SetField(TiffTag.GEOTIFF_MODELPIXELSCALETAG, GEOTIFF_MODELPIXELSCALETAG.AsObjectArray());
      output.SetField(TiffTag.GEOTIFF_MODELTIEPOINTTAG, GEOTIFF_MODELTIEPOINTTAG.AsObjectArray());
      output.SetField(TiffTag.GEOTIFF_GEOKEYDIRECTORYTAG, GEOTIFF_GEOKEYDIRECTORYTAG.AsObjectArray());
      output.SetField(TiffTag.GEOTIFF_GEOASCIIPARAMSTAG, GEOTIFF_GEOASCIIPARAMSTAG.AsObjectArray());

      // compression is optional
      output.SetField(TiffTag.COMPRESSION, Compression.ADOBE_DEFLATE);

      // fill samples array
      byte[][] buffer = new byte[height][];
      for (int j = 0; j < height; j++)
      {
        buffer[j] = new byte[width];
        for (int i = 0; i < width; i++)
          buffer[j][i] = (byte)(j * width + i);
      }

      for (int j = 0; j < height; ++j)
        output.WriteScanline(buffer[j], j);
    }
  }
}