Common GIS Data Outputs

Orthomosaic / Orthophoto:

Also referred to as an Ortho, this is generated from thousands of images stitched together (left image below) to show one large high-resolution 2D image with measurable qualities (right image below).

The resolution of an Ortho is specified in GSD (Ground Sampling Distance). For example, a 5cm Ortho means that every pixel in the image represents 5cm on the ground. It is geometrically corrected to ensure a uniform and accurate scale, so it can be used to calculate accurate distances.

An ortho typically shows a top-down / birds-eye-view of a site and is most commonly used as the background to a topographic map which shows different features of the land and is an essential tool in planning and development.

Point Cloud:

A point cloud is a set of 3-dimensional data points (defined by x, y and z coordinates).

These points can be triangulated to produce a model of the surface based on each point’s elevation value i.e. Digital Surface Model. A classified point cloud means that natural and man-made objects have been categorised, and can be filtered out to reveal only the ground points i.e. Digital Terrain Model.

Digital Surface Model:

A digital surface model represents the surface of the land including all natural and built features (trees, rocks, buildings, machinery).

DSMs are useful in analysing terrain for urban planning – like checking how a proposed structure would obstruct views or detecting vegetation encroachment on power lines. They can also used for identifying mine stockpiles for volume calculations.

Digital Terrain Model:

When non-ground points (trees, buildings, structures etc) are filtered out leaving only bare-earth, a model of this surface is represented by a digital terrain model – a clear visual of the ground surface only.

A DTM is particularly useful in planning with respect to hydrology (flood & drainage analysis), soils and land-use/development.

DSM vs DTM:

This diagram shows the difference between a DSM and DTM surface.

DSM and DTM are different types of Digital Elevation Models (DEMs)

Contours:

Contours are lines that connect points of equal elevation values. The contour interval is the vertical distance between contour lines.

Contours visually depict the layout of the terrain- lines with wide spacing indicate flat areas while lines close together represent steeper slopes.

Contours are used to show topography on a map and to understand terrain elevations.

3D Model:

A 3D model is a representation of a real object or scene. 3D models show heights/elevations, not just the location of features and allow you to make highly accurate measurements off the digital model.

Depicting real world environments helps in planning and understanding patterns over time. A reality model of a structure or asset, also known as its digital twin, is useful in developing asset inventories, inspecting for defects or in planning further development of the asset.