03- elevation data Stored in a geotiff 

Created: January10, 2024  Updated: January10, 2024

What is a Geotiff ?

GeoTIFFs files are raster image file types that are commonly used to store satellite and aerial imagery data, along with geographic metadata that describes the location in space of the image. GeoTIFFs are compatible with nearly all CAD and GIS applications and maintain their quality when compressed, edited, and transferred. In drone mapping workflows, GeoTIFFs can contain both orthophotos and digital elevation models (DEMs).

When it comes to georeferenced imagery used in digital mapping—like drone-collected survey data, for instance—there’s no greater vessel than the GeoTIFF. This trusted, widely-used file format is used to store, transfer, and display large image files that also contain contextual geographic information.

What is a GeoTIFF metadata file ?

The contained metadata tags in GeoTiffs help describe the actual location that each and every pixel represents. When uploaded to a GIS application, like ArcGIS or QGIS, they make it possible to position the image in context of the real world.

Information included in these metadata tags include:

Coordinate systems: The grid of X and Y units (and Z if three-dimensional) used to describe the location of each point on a map.

Ellipsoids and geoids: Ellipsoids are estimated models of the Earth’s shape (not accounting for changes in elevation) that are used in determining horizontal coordinates. Geoids are more dynamic models of the earth that do consider the undulations of the planet’s surface and are used to determine elevation. (Check out our complete explainer on ellipsoids and geoids.)

Datums: Horizontal datums pin an ellipsoid to a specific location in space. Vertical datums take the surface of a geoid (or the Mean Sea Level) and establish it as a zero-point for elevation. (And here’s where we break down datums in full detail.) Projection: Mathematical rules for taking data for a three-dimensional space and transforming it into a two-dimensional display (aka a map).

Essentially, GeoTIFF files contain information about your data’s coordinate reference system (CRS). Think of CRSs as languages that help geospatial datasets speak together. If you try to use multiple datasets that have been referenced through different CRSs together in a GIS package, their coordinates will not line up, making measurements between them useless.

What is a DEM file ?

DEMs represented as a single band variation of the GeoTIFF format where each point or pixel having an elevation value. In this case, the single value per pixel is interpreted as vertical elevation and used to build and display a 3D digital elevation model. 

What is a Grayscale GeoTIFF file ?

Single-band raster data contains a single value per pixel. This translates to an array of values that can be interpreted as colors to create an image or elevation value to build a terrain model. While there are a few ways in which a single value pixel can be interpreted and used, the most basic is a grayscale image. 

Data in GeoTIFF format is stored as binary values at different scales. A grayscale GeoTIFF image can be generated in Global Mapper using 1-bit, 8-bit, 16-bit, or 32-bit values. Bit values work in binary, a base two system, so a single bit image has  21 possible values, an 8-bit image has 28, a 16-bit image has 216, and so on. Overall, the higher the bit value for the file the more possible values can be assigned to individual pixels. The most common variants are  8- or 16-bit images that contain values 0 to 255 or 0 to 65535 respectively. 

What is a Multiband GeoTIFF file ?

While there are many ways to utilize and analyze single-band raster data, the GeoTIFF format is able to store multiple bands of data in a single file. Multiband data contains multiple values per pixel, which effectively compresses multiple single-band layers into a single layer. Combining multiple data values per pixel in a single file allows the values to be combined for data display. 

GIS Terrain Loader Pro is able to read elevation + metadata from three GeoTiff's formats:

• DTM Geotiff                   (Download Example)

• GrayScale Geotiff          (Download Example)

• Multi-Bands GeoTiff      (Download Example)