LibTiff C# - Getting coordinates

Question

I am using the LibTiff.NET library to load GeoTiff data in C# (inside Unity). **NOTE - I looked at GDAL also, but faced similar issues as outlined below, and would much prefer to use LibTiff if possible.

I would ultimately like to be able to take a lat/long value and have a function that returns a chunk of pixel data for a 50m area around that point, streamed from a GeoTiff image on disk (not storing whole image in RAM).

I have a test file that is representative of what my software will be given in production.

I am trying to figure out how to read or compute the lat/long extents of the test file image, as I can't find a good tutorial or sample online which contains this functionality.

I can read the width+height of the file in the TiffTags, but many other values that seem critical for computing the extents such as X and Y resolutions are not present. It also appears like the lat/long extents (or a bounding box) are not present in the tags.

At this point I am led to believe there may be more tags or header data that I am not familiar with because when I load the test file into Caris EasyView I can see a number of properties that I would like to read or compute from the file:

Is it possible to obtain this data using LibTiff? Or is there a better system I should use? (wrapped GDAL maybe?)

** NOTE: I cannot link the test file due to NDA, plus it's enormous

Answer 1

This is for a 32-bit geotiff:

int width = tiff.GetField(TiffTag.IMAGEWIDTH)[0].ToInt();
int height = tiff.GetField(TiffTag.IMAGELENGTH)[0].ToInt();

int samplesPerPixel = tiff.GetField(TiffTag.SAMPLESPERPIXEL)[0].ToInt();
int bitsPerSample = tiff.GetField(TiffTag.BITSPERSAMPLE)[0].ToInt();
int bytesPerSample = bitsPerSample / 8;

byte[] scanline = new byte[tiff.ScanlineSize()];
float[] scanline32Bit = new float[tiff.ScanlineSize() / 4];//divide by 4 for byte word 

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

FieldValue[] modelPixelScaleTag = tiff.GetField(TiffTag.GEOTIFF_MODELPIXELSCALETAG);
byte[] modelPixelScale = modelPixelScaleTag[1].GetBytes();
double pixPerLong = BitConverter.ToDouble(modelPixelScale, 0);
double pixPerLat = BitConverter.ToDouble(modelPixelScale, 8) * -1;