How to add metadata such as geokeydirectory, geoasciiparams, modelpixelscale and modeltiepoint to a compressed tiff image?

Adding Metadata to Compressed TIFF Images: A Human’s Guide

TIFF images – you’ve probably run into them if you’ve ever worked with anything from satellite imagery to scanned documents. They’re the workhorses of the raster graphics world, especially when you need to pack a lot of information into a single file. One of the coolest things about TIFFs is their ability to store metadata, that “data about data” that tells you everything you need to know about the image itself. And when it comes to geospatial data, that metadata is pure gold.

Think of geospatial metadata as the secret sauce for making sure your images know where they are in the world. We’re talking about things like georeferencing info, which is absolutely critical for anyone doing spatial analysis or mapping. So, how do you actually add this stuff – things like GeoKeyDirectory, GeoAsciiParams, ModelPixelScale, and ModelTiepoint – to a compressed TIFF? Let’s break it down.

First, a quick primer on those cryptic-sounding tags:

• GeoKeyDirectory: This is basically the GeoTIFF’s brain. It’s like a table of contents that points to all the other important geospatial info. Without it, your software is going to be lost.
• GeoAsciiParams: This is where you can stash any extra text that describes the image’s georeferencing. Projection names, datums, any little notes that help someone understand the image’s spatial context – it all goes here.
• ModelPixelScale: Ever wonder how big each pixel is in real-world units? This tag tells you! It defines the pixel size in meters (or feet, or whatever unit you’re using), so your software knows how to translate pixels into distances on the ground.
• ModelTiepoint: Imagine sticking pins into a map. That’s what ModelTiepoint does. It links specific pixels in your image to known locations on Earth. These tie points are what “anchor” your image to the real world.

Okay, so you know what these tags are. Now, how do you use them?

Well, you’ve got options. There are a bunch of tools out there, but here are a few of the big names:

• GDAL (Geospatial Data Abstraction Library): GDAL is like the Swiss Army knife of geospatial tools. It’s a command-line powerhouse that can read, write, and manipulate just about any geospatial data format you can throw at it, including TIFF. It might seem a little intimidating at first, but trust me, it’s worth learning.
• libtiff: This is a lower-level library specifically for working with TIFF images. If you’re a programmer and need fine-grained control over TIFF files, libtiff is your friend.
• ExifTool: Think of ExifTool as the metadata whisperer. It’s a command-line tool that can read and write metadata in tons of different file formats, including TIFF. It’s super easy to use, which makes it a great option for quick metadata edits.

For most people, GDAL is going to be the best choice. It’s powerful, flexible, and widely supported. So, let’s walk through an example using GDAL: