geotiff.net

A (WIP) port of geotiff.js to .Net.

This project adds native .Net handling of geotiff files, the benefits being:

• Easier cross platform compatibility (over GDAL which requires native dependencies to be compiled on the target platform)
• Asynchronous and streamed reads + writes
• Easier debugging
• Extensability in C# (e.g. define your own source types, decoders, sidecar file handlers)

Examples

Read everything as a 2D array from the first sample of the first image from a file:

var lonLatTif = Path.Combine(GetDataFolderPath(), "elevationData.tif");
await using var fsSource = new FileStream(lonLatTif, FileMode.Open, FileAccess.Read);
var geotiff = await GeoTIFF.FromStream(fsSource);
int count = await geotiff.GetImageCount();
var image = await geotiff.GetImage();
var readResult = await image.ReadRasters<int>();
var sampleResult = readResult.GetSampleResultAt(0).To2DArray();

Read data at the pixel at a coordinate from an AWS S3 bucket:

using var client = new AmazonS3Client(new AmazonS3Config { ... });
var gtAWSClient = new GeotiffAWSClient("testbucket", "modelOutputDataCOG.tif", client);
GeoTIFF? geotiff = await GeoTIFF.FromRemoteClient(gtAWSClient);
var image = await geotiff.GetImage();
var result = await image.ReadValueAtCoordinate<double>(lon, lat); 
var waterVelocityAtCoordinate =  result.GetSampleResultAt(0).FlatData.GetValue(0);
var waterDepthAtCoordinate = result.GetSampleResultAt(1).FlatData.GetValue(0);

Read data from a file that has external overviews in an .ovr sidecar file

var externalOverviewTifPath = Path.Combine(GetDataFolderPath(), "external_overviews.tif");
var ovrFilePath = externalOverviewTifPath + ".ovr";

await using var mainStream = File.OpenRead(externalOverviewTifPath);
await using var ovrStream = File.OpenRead(ovrFilePath);

var overviewMultiTiff = await MultiGeoTIFF.FromStreams(mainStream, new[] { ovrStream });
var imageCount = await overviewMultiTiff.GetImageCount();// 4; 1 from the main file and 3 from the overviews.
var hasOverviews = await overviewMultiTiff.HasOverviews(); // true

Alternatives libraries

Other than GDAL, there are several packages for reading (and possibly writing) geotiffs.

• GDAL through gdal.netcore - Quite low level. Synchronous. Packages up GDAL for you so you don't have to compile it + the C# bindings yourself.
• ImageSharp - Does not support geotiff tags, COGs or spatial operations, synchronous.
• Mission controller - Does not support COGs or spatial operations, synchronous. Tailored to the requirements of Ardupilot itself.
• DEM.NET - a wrapper around LibTiff.Net. Synchronous. Only filesystem files supported.

Contributing

This project is a WIP, new contributors are very welcome. If you’d like to get involved, please open an early PR or start a discussion to share your ideas. Some ideas of good items to work on:

Before release, the bare minimum:

• Handle case where the user does not know the type of the raster data before reading it, e.g. in cases where they are reading a user-passed tiff file.
• Image resampling
• User examples
• More friendly handling of NO_DATA values in general through MaskedGeoTIFFReader
• BigTIFF is working well, but needs some tests to cover it.
• Also some tests for cases where precision is important.
• Handle http servers that respond in different ways in GeotiffHTTPClient.cs - check todo comments in that file.
• Allow users to specify which samples they want to read rather than reading all of them.

Post initial release:

• Offer up a synchronous API too for legacy codebases and environments where that is preferred.
• Benchmarking
• Writing, particularly to COG format with overviews
• GeotiffAzureClient
• JPEG compression and decompression
• More spatial operation support - currently only ReadValueAtCoordinate is supported
• Support multi-threading/ parallel?

Compliance tests

The Compliance tests are a set of that compare the read tag and pixel read values between geotiff.js and geotiff.net. The tifs are not kept under version control, but are downloaded from OSGeo's website which is a good sample set to test against.