Anatomy of a Digital Elevation Model

An elevation model is a digital twin of a landscape that creates a realistic context for analysis and design in a variety of applications. Autonomous drones now provide means of collecting elevation models frequently and with high level of detail. At the same time, cloud computing and web technology enables fast data processing and ubiquitous delivery of maps and analysis tools.

This article illustrates how the Voxxlr cloud application facilitates the analysis of digital elevation models collect by drones. Voxxlr runs entirely online and there is no need to install software. All data is processed and stored in the cloud and accessible on demand via a web browser. You can examine the map used in this article in a viewer or editor using Google Chrome.

Processing and Visualization

Voxxlr fuses color and elevation data into a multi resolution 2D map. Its scalable cloud infrastructure can process very large data sets consisting of billions of samples in a short period of time. For example, the map below contains a 2-kilometer section of an agricultural drainage canal consisting of 225,000 by 54,000 pixels at 9 mm resolution. While serving large maps online is not new, the high resolution achieved by a low flying drone and the short delay between data collection and delivery have only recently become possible.

The elevation data contained within each pixel enables a variety of useful 3D visualization techniques. Hill shading, for example, reveals small changes in topography which are otherwise indistinguishable. The different coloration of slope and altitude help to assess the state of the canal and identify areas which require further inspection. The left hand side of the image below clearly shows erosion into the adjacent field. The same breach is almost undetectable in the color image to the right.


Voxxlr provides simple geometric primitives such as lines, polygons and flood filled regions to extract a variety of metrics including distances, angles, areas, volumes and elevation profiles. Unlike most online map servers which generally apply spherical map projections to allow for seamless navigation across the globe, Voxxlr uses a planar projection that preserves distances and angles. Measurements are thus as accurate as the resolution of the original data allows.

Line Tool

A line measures distances and angles. It also plots the elevation along its path to create a profile of the underlying topography. The image below shows a straight line across the erosion including the corresponding elevation profile. The graph helps to assess the damage to the field and estimate repair efforts. The vertical green bar in the chart corresponds to the yellow control point on the line, allowing for close correspondence between the chart and the map.

A segmented line can produce a profile along a curved path. In the image below, this capability is used to measure the slope of the road as it turns around a bend. The chart reveals how the road evenly declines 11 meters over a distance of 150 meters. The vertical red lines in the chart indicate the split points corresponding to the green control points on the map.

Polygon Tool

In addition to distances and angles, a polygon also measures areas as well as the volume above or below the polygonal plane. The following image illustrates how the polygon tool computes the volume of the erosion in the canal. The blue control point locks the elevation of the plane to that of the underlying pixel, providing fine control over the region included in the calculation. The green scan line shows the current progress and the panel on the left contains the values computed so far.

This measurement covers only about a 10 by 10 meter section of the 2-kilometer long map. The entire elevation model can be accessed seamlessly at various levels of detail. As the map is decomposed of a multi-resolution hierarchy, the accuracy of a measurement depends on the current zoom level of the viewer. While the absolute error increases with the zoom level, the percentage error relative to the magnitude of the measurement remains constant.

Flood Fill

The Flood Fill widget computes the volume and area of connected regions below or above the height of an initial reference point. It is similar to a Magic Wand in a paint program, except that pixel height rather than color defines the selection threshold. In the image below, the flood fill widget measures the capacity of the canal within a specific region. Similar to the polygon, the blue elevation control point defines the initial search height.


The map used in this article was produced by INDrone Aero Systems. For an interactive demo, follow this link to the viewer or editor. Click on the viewpoints on the top right as well as the various information icons. In order to analyze your own data sets, visit and log in to access the upload screen. Always make sure to use Google Chrome to visit Voxxlr.

If you are interested in learning more about Voxxlr, connect or send an email to