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Is there a legend or key for the DSMs and DTMs?
Is there a legend or key for the DSMs and DTMs?

How to interpret the color ramp display for the DSM and DTM products

Karen Joyce avatar
Written by Karen Joyce
Updated over a week ago

Drone mapping datasets are processed to create three key products - the orthomosaic, digital surface model (DSM). and digital terrain model (DTM) as below.

What do the colors mean?

DSM and DTM colors are displayed on a continuous scale from blue to green to yellow. This is known as the viridis color palette. While you might be used to seeing the rainbow used in other visualizations, viridis is far better for presenting data, and is friendly to those with color perception difficulties. You can learn more about that in our blog here if you're interested.

viridis color ramp from low values in dark blue through to green as medium and yellow as high

Each color ramp is specific and relative to the dataset it represents. This means that the color you see in one dataset will not necessarily represent the same elevation value in another.

For example, the color ramp above might represent 0-100 m elevation in one dataset, but 20-30 m in another.

If there is an outlier value in the dataset - either very high or very low - this can also skew the way your data are represented.

Extracting the DSM / DTM values

Most importantly, the actual values calculated in your DSM and DTM are retained in the pixel value, regardless of the color visualization on the platform. So if you need to know the values or want to change the color ramp, download the products and you will be able to work with their symbology in a GIS or image processing software.

Are the DSM / DTM values accurate?

The pixel values within these products should be considered as relative rather than absolute. This means that within any one dataset, you should be able to relatively compare one area of the scene to another to say one area is higher or lower in elevation. If you need absolute elevation values, it is important to include ground control points as part of your pre- or post processing routines.

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