Converting SRTM to XYZ, ORD, and GRD: Essential Techniques for Earth Science and GIS Applications

Decoding Earth: Turning SRTM Data into XYZ, ORD, and GRD – A Practical Guide

Ever wondered how we get those amazing 3D maps of the Earth? A big part of it comes from something called the Shuttle Radar Topography Mission, or SRTM for short. This mission gave us a near-global digital elevation model (DEM), which is basically a detailed height map of our planet. But raw data is rarely useful on its own. To really put this data to work in earth science and GIS (Geographic Information Systems), we need to know how to convert it into different formats like XYZ, ORD, and GRD. Think of it like translating languages – each format speaks to different software and has its own way of doing things. Let’s dive in!

SRTM: A Bird’s-Eye View (From Space!)

Back in February 2000, SRTM used some pretty cool space-based radar to map the Earth’s surface i. This wasn’t just any radar; it was Interferometric Synthetic Aperture Radar (InSAR), a fancy term for a technique that bounces radar signals off the ground and measures the reflections to figure out the elevation. The result? A super comprehensive DEM covering about 80% of the Earth, from 60 degrees North all the way down to 56 degrees South i. That’s a huge chunk of the planet! The C-band radar data was used to create near-global topographic maps of Earth called Digital Elevation Models (DEMs) i. Data from the X-band radar were used to create slightly higher resolution DEMs but without the global coverage of the C-band radar i.

The best part? SRTM data is available to everyone through various government and scientific websites i. You can download it and start playing around, which is awesome.

Understanding SRTM Flavors: Versions and Formats

Not all SRTM data is created equal. There are different versions, each with its own quirks and level of polish.

• Version 1: Think of this as the “raw” footage – almost untouched i.
• Version 2.1: A bit tidier than Version 1, with some processing errors fixed and water boundaries cleaned up. Still, it might have some “voids,” or missing data i.
• Version 3 (SRTM Plus or Void Filled): The most complete version. Here, the voids have been filled in using data from other sources, like ASTER GDEM i.

The data itself comes in 1°x1° tiles i. These tiles are zipped up, and inside each zip file, you’ll find an HGT file. The name of the HGT file tells you the coordinates of the southwest corner of the tile (e.g., N20E100.hgt covers the area from 20°N to 21°N and from 100°E to 101°E) i. Inside the HGT file are a bunch of 16-bit integers, which are basically the height of each point in meters, arranged in a grid i.

SRTM to XYZ: Making Points

The XYZ format is super simple: it’s just a list of points with their X (Longitude), Y (Latitude), and Z (Elevation) coordinates i. Converting SRTM to XYZ is a common task because it’s a flexible format that can be used in tons of different programs.

How to do it:

SRTM to ORD: A Different Beast

Okay, this one’s a bit of an outlier. The ORD file format isn’t typically used for geospatial data. It’s mostly associated with ILOG CPLEX, a mathematical optimization software i. In that world, an ORD file specifies priority orders for variables in a programming problem i. Variables that are not given an explicit priority or that do not appear in an ORD file are assigned 0 (zero) priority i.

So, you wouldn’t directly convert SRTM to ORD. Instead, you’d extract the elevation values from the SRTM data and use them as inputs in your optimization model.

SRTM to GRD: Grid It Up!

GRD is another format for gridded data, and it often refers to the ESRI ArcInfo ASCII grid format or the Golden Software Surfer grid format i. Think of it as a way to store raster data, like our elevation model.

Here’s how to convert to GRD:

Putting It All to Work: Real-World Applications

Once you’ve converted your SRTM data, the possibilities are endless. Here are just a few examples:

• Topographic Mapping: Creating detailed maps for hiking, urban planning, you name it i.
• Watershed and Hydrology Analysis: Figuring out where water flows, which is crucial for managing water resources and predicting floods i.
• Geological Surveys: Studying landforms and identifying potential hazards like landslides i.
• Infrastructure Development: Planning roads, pipelines, and other infrastructure projects i.
• Natural Disaster Management: Assessing flood risk and helping with disaster response i.
• Climate Research: Using topography data in climate models because topography determines factors like air and water flow i.
• Geomorphic Change Detection analysis: SRTM and ASTER DEMs are being used for Geomorphic Change Detection analysis because of its mission specified accuracy i.

The improved resolution of SRTM data has made a real difference in things like flood mapping and volcano hazard assessments i.

Final Thoughts

Converting SRTM data is a key skill for anyone working with geospatial data. While XYZ and GRD conversions are everyday tasks, ORD is more specialized. Get comfortable with these techniques, and you’ll be well on your way to unlocking the power of SRTM data for all sorts of exciting applications.