How to get GeoTiff world-positioning metadata using libtiff.net

I am trying to get the bounding-box of a GeoTiff file from the ALOS dataset (JAXA):

Tiff terrainTiff = Tiff.Open(@"Assets/Project/Heightmaps/" + "N046E007" + "/ALPSMLC30_" + "N046E007" + "_DSM.tif", "r");
                FieldValue[] modelPointTags = terrainTiff.GetField(TiffTag.GEOTIFF_MODELTIEPOINTTAG);
                foreach (FieldValue modelPointTag in modelPointTags)
                {
                    System.Type valueType = modelPointTag.Value.GetType();
                    Debug.Log(modelPointTag.Value.ToString());
                    Debug.Log(valueType);
                }

There are 2 values in modelPointTags: System.Int32 and System.Byte[]. How to I proceed reading world-positioning metadata?

Solution

how about using libtiff

 using (Tiff tiff = Tiff.Open(fileName, "r"))
        {
            //Image size
            int nWidth = tiff.GetField(TiffTag.IMAGEWIDTH)[0].ToInt();
            int nHeight = tiff.GetField(TiffTag.IMAGELENGTH)[0].ToInt();
            float[,] heightMap = new float[nWidth, nHeight];
            FieldValue[] modelPixelScaleTag = tiff.GetField(TiffTag.GEOTIFF_MODELPIXELSCALETAG);
            FieldValue[] modelTiePointTag = tiff.GetField(TiffTag.GEOTIFF_MODELTIEPOINTTAG);

            byte[] modelPixelScale = modelPixelScaleTag[1].GetBytes();
            double dW = BitConverter.ToDouble(modelPixelScale, 0);
            double dH = BitConverter.ToDouble(modelPixelScale, 8) * -1;

            byte[] modelTransformation = modelTiePointTag[1].GetBytes();
            double originLon = BitConverter.ToDouble(modelTransformation, 24);
            double originLat = BitConverter.ToDouble(modelTransformation, 32);

            double startW = originLon + dW / 2.0;
            double startH = originLat + dH / 2.0;

            FieldValue[] tileByteCountsTag = tiff.GetField(TiffTag.TILEBYTECOUNTS);
            long[] tileByteCounts = tileByteCountsTag[0].TolongArray();

            FieldValue[] bitsPerSampleTag = tiff.GetField(TiffTag.BITSPERSAMPLE);
            int bytesPerSample = bitsPerSampleTag[0].ToInt() / 8;

            FieldValue[] tilewtag = tiff.GetField(TiffTag.TILEWIDTH);
            FieldValue[] tilehtag = tiff.GetField(TiffTag.TILELENGTH);
            int tilew = tilewtag[0].ToInt();
            int tileh = tilehtag[0].ToInt();

            int tileWidthCount = nWidth / tilew;
            int remainingWidth = nWidth - tileWidthCount * tilew;
            if (remainingWidth > 0)
            {
                tileWidthCount++;
            }

            int tileHeightCount = nHeight / tileh;
            int remainingHeight = nHeight - tileHeightCount * tileh;
            if (remainingHeight > 0)
            {
                tileHeightCount++;
            }

            int tileSize = tiff.TileSize();
            for (int iw = 0; iw < nWidth; iw += tilew)
            {
                for (int ih = 0; ih < nHeight; ih += tileh)
                {
                    byte[] buffer = new byte[tileSize];
                    tiff.ReadTile(buffer, 0, iw, ih, 0, 0);
                    for (int itw = 0; itw < tilew; itw++)
                    {
                        int iwhm = ih + itw;
                        if (iwhm > nWidth - 1)
                        {
                            break;
                        }
                        for (int ith = 0; ith < tileh; ith++)
                        {
                            int iyhm = iw + ith;
                            if (iyhm > nHeight - 1)
                            {
                                break;
                            }
                            heightMap[iwhm, iyhm] =
                              BitConverter.ToSingle(buffer, (itw * tileh + ith) * 4);

                            Console.WriteLine(heightMap[itw, ith]);
                        }
                    }
                }
            }
        }