Stereoscopic Imagery

Stereoscopic imagery is the method for enhancing an illusion of three-dimensional (3D) vision by displaying two slightly offset images separately to each eye. This duplicates the binocular vision of humans allowing one to observe depth and spatial relationships. Stereoscopic imagery is used in many applications within GIS such as photogrammetry, topographic mapping and environmental modeling.

Fundamentals of Stereoscopic Imagery

Stereopairs: Two images of the same area collected from different points like satellite or aerial photosystems and then do it from many angles and have them view it from different viewpoints, the variation of viewing angle introduces the parallax that you use for 3D reconstruction.

Parallax: This means the difference in the position of an object with respect to two observers. Parallax is also important to infer depth in stereoscopic imagery. The word parallax is not something captured in real life however it is a processing effect.

Stereoscopic Measurement: An approach for measuring relative elevation using stereopair where GIS professionals can measure the height of terrain features by locating corresponding points in left and right images. That work is usually automated through digital photogrammetry software.

Science behind Stereoscopic Imagery

Data Capture: Stereoscopic Imagery starts by capturing high-resolution data with remote sensing platforms such as satellites or aircraft. These platforms have cameras that can take photos are slight offset angles, to make it a stereopair.

Calibration and Orientation of Images: To extract precise 3D information, the image should be geographically rectified as well as oriented. This consists of interior and exterior orientation where the image is corrected for distortions caused by the camera lens and aligned to real-world coordinates respectively.

Parallax Measurement: The distance between two stereopair images is then measured by professionals where the parallax values are used to determine the elevation of various geographical points.

Digital Elevation Model (DEM): As stated earlier, one of the prime inputs of stereoscopic image handling to GIS is the Digital Elevation Model. A DEM shows the 3D topological surface of terrain that can be derived by interpolation of height data from each pair. On the other hand, DEMs have been utilized in superseding fields in GIS such as hydrology, land-use planning and risk management of natural disasters.

Applications of Stereoscopic Imagery

Topographic Mapping: It is one of the most traditional applications of stereoscopic imagery in GIS where better maps are created by extracting terrain data from stereopairs and generating contour lines, spot heights and many other relational attributes.

LULC Analysis: Land cover land use analysis allows detailed LCLU maps made achievable through Stereoscopic imagery. In Vegetation, Urban, Water Areas and other land cover classifications, GIS Specialists use the height and shape of features to derive different land cover types.

Urban Planning and Infrastructure Development: In city environments, stereoscopic imagery is employed to model buildings, roads and different infrastructure parts in 3-D. City planners and engineers use these models to assess the current state of development, plan for future growth and simulate the impacts of the latest infrastructure.

Disaster management: An important aspect of planning disaster risk reduction and response is the production of accurate 3D terrain models from stereoscopic imagery. For example, in areas prone to floods, DEMs created from stereopairs can assist in delineating areas threatened with flooding. Likewise, in areas of seismic activity, terrain models allow for the simulation of earthquake consequences and lay out possible evacuation paths.

Forestry / Agriculture: Stereoscopic Imagery is used to monitor forest canopy structure, estimate timber volume and detect deforestation. It is also being used to capture crop health analysis, growth patterns and optimize precise farmland techniques.

Environmental surveillance- Stereoscopic imagery is important for monitoring developments in the natural environment. These models help environmental scientists to study the effect of climate change on habitat and hence plan conservation efforts as well.

Tools and Technologies

Stereoscopic Viewing Systems: GIS specialists utilize a variety of stereo-based hardware for 3D viewing like stereoscopes and digital stereoscopic workstations which are used for displaying 3D views on computer screens with the help of polarized or anaglyph glasses.

Digital Photogrammetry Software: Tools for processing stereoscopic images include the digital photogrammetry software ERDAS IMAGINE, PCI Geomatics and Leica Photogrammetry Suite (LPS). They allow for automatic extraction of elevation data and DEM/orthophoto generation from stereopairs causing problems for many people.

LiDAR Integration: LiDAR is used to create high-detail 3D models. Using LiDAR (Light Detection and Ranging) data, you can combine it with stereoscopic imagery for stunning 3D modeling. LiDAR measures the delay time of laser pulses reflected surface and realizes accurate elevation data. Integration of LiDAR with stereoscopic imagery can provide higher resolution and more accurate DEMs.

Automated Feature Extraction: Recent GIS tools use machine learning and computer vision algorithms with stereoscopic imagery to extract things such as buildings, trees or roads. These algorithms which look at the parallax between stereopairs, identify and classify objects with little human input.

The GIS industry makes heavy use of stereoscopic imagery to develop thorough 3D models of the terrain on Earth. It has a myriad of applications including topographic mapping, urban planning, environmental monitoring and disaster management. As technology continues to improve, standards in stereoscopic imagery will also undoubtedly increase and with that the importance of it in GIS. Still, the problems of data processing costs and terrain complexity need to be resolved before realizing this potential fully.