Digital Elevation Model (DEM) Data

About DEM Data

Mission information

A DEM is a digital model or 3D* representation of a terrain's surface. With a DEM you are able to obtain and analayse heights within your area of interest, and integrate the data in 3D applications. The data can also be used for the orthorectification of satellite imagery (e.g., Sentinel 1). Sentinel Hub supports Mapzen's DEM, available through Amazon Web Services (AWS) through EU-Central-1 and US-West-2 regions, and Copernicus DEM, available through AWS EU-Central-1 region.

Mapzen DEM is based on SRTM30 (Shuttle Radar Topography Mission) and other sources. Bathymetry data is taken from ETOPO1. It is a static collection and does not depend on the date. More information: Mapzen's documentation.

Copernicus DEM is based on WorldDEM that is infilled on a local basis with the following DEMs: ASTER, SRTM90, SRTM30, SRTM30plus, GMTED2010, TerraSAR-X Radargrammetric DEM, ALOS World 3D-30m. We provide two instances named COPERNICUS_30 and COPERNICUS_90, with worldwide coverage. COPERNICUS_90 uses COP-DEM GLO-90, which has 90 meters resolution. COPERNICUS_30 uses COP-DEM GLO-30 Public, which has 30 meters resolution, where it's available, and for the rest is uses GLO-90. Tiles that are missing from GLO-30 Public are not yet released to the public by Copernicus Programme. Both instances are static and do not depend on the date. We return a homogeneous DEM with zeros in regions where there are no source tiles (e.g. in ocean areas). More information here.

*Actually, we should say "2.5D" to be more precise. The terrain surface embedded in 3D space is modeled in a way that precisely one height is assigned to each pixel. This brings limitations as not all 3D shapes (e.g., overhangs, vertical walls, caves) can be fully modeled.

Attribution and use

For Mapzen DEM, see terms here.

For Copernicus DEM GLO-90, check the terms at the bottom, where it says "Licence for COP-DEM-GLO-90-F Global 90m Full, Free & OpenLicence for the use of the Copernicus WorldDEM™-90".

For Copernicus DEM GLO-30 Public, check the license and terms here.

Accessing DEM Data

To access data you need to send a POST request to our process API. The requested data will be returned as the response to your request. Each POST request can be tailored to get you exactly the data you require. To do this requires setting various parameters which depend on the collection you are querying. This chapter will help you understand the parameters for DEM data. To see examples of such requests go here, and for an overview of all API parameters see the API Reference.

Endpoint Locations

Data type identifier: dem

Use dem (previously DEM) as the value of the input.data.type parameter in your API requests. This is mandatory and will ensure you get DEM data.

Filtering Options

This chapter will explain the input.data.dataFilter object of the DEM process API.

demInstance

Sets the used DEM. By default, when it's not set, it uses Mapzen's DEM.

Processing Options

This chapter will explain the input.data.processing object of the DEM process API.

Available Bands and Data

Information in this chapter is useful when defining input object in evalscript. A string listed in the column Name can be an element of the input.bands array in your evalscript.

*dataMask has no source resolution as it is calculated for each output pixel.

Units

The data values for each band in your custom script are presented in the units as specified here. In case more than one unit is available for a given band, you may optionally set the value of input.units in your evalscript setup function to one of the values in the Sentinel Hub Units column. Doing so will present data in that unit. The Sentinel Hub units parameter combines the physical quantity and corresponding units of measurement values. As such, some names more closely resemble physical quantities, others resemble units of measurement.

The Source Format specifies how and with what precision the digital numbers (DN) from which the unit is derived are encoded. Bands requested in DN units contain exactly the pixel values of the source data. Note that resampling may produce interpolated values. DN is also used whenever a band is derived computationally (like dataMask); such bands can be identified by having DN units and N/A source format. DN values are typically not offered if they do not simply represent any physical quantity, in particular, when DN values require source-specific (i.e. non-global) conversion to physical quantities.

Values in non-DN units are computed from the source (DN) values with at least float32 precision. Note that the conversion might be nonlinear, therefore the full value range and quantization step size of such a band can be hard to predict. Band values in evalscripts always behave as floating point numbers, regardless of the actual precision.

The Typical Range indicates what values are common for a given band and unit, however outliers can be expected.

For DEM, DN (digital numbers) are the default and only unit. DN values equal elevation.

*Occasionally FLOAT32 for MAPZEN and always FLOAT32 for Copernicus DEM.

Scene Object

The evalscript evaluatePixel scene object is not returned/is null when requesting DEM.

Collection specific constraints

DEM values are in meters and can be negative for areas which lie below sea level (e.g. ocean areas or much of the Netherlands). When requesting a DEM a simple way to mitigate this is to set the output format in your evalscript to sampleType: SampleType.FLOAT32. More about output formats can be found here.

For output formats sampleType: SampleType.UINT8 and sampleType: SampleType.UINT16 be careful as negative values can be misinterpreted due to signedness issues as well as potential problems due to integer overflow. For example:

• sampleType: SampleType.UINT8 - a height of 256 meters will be encoded as 0 in such a file due to overflow. A height of -1 meter will be encoded as 255.
• sampleType: SampleType.UINT16- a height of -15 meters for instance will be encoded as 65520.

One way to handle this adjustment is to ensure there are no negative values in the output by adding a constant to DEM values, e.g. 12000 (the minimum value in DEM is not smaller than -11000 m). If you need actual DEM values (i.e. heights), the constant 12000 must be subtracted from the output values outside of Sentinel Hub.

//VERSION=3

function setup() {
  return {
    input: ["DEM"],
    output:{
        id: "default",
        bands: 1,
        sampleType: SampleType.UINT16
    }
  }
}

function evaluatePixel(sample) {
  return [sample.DEM + 12000]
}

Examples

DEM examples