4 Types Of Geospactial Data Explained
1. Aerial Surveys – Orthophoto & Stereo Photography
Orthophoto
When an aerial photograph is geometrically corrected for distortions caused by topographic relief, lens distortion and camera tilt, it becomes ortho rectified.
Who uses orthophoto and for what?
Orthophotos have a uniform scale, providing an accurate representation of the earth’s surface and it is used to measure true distances. This makes the imagery easily integrated into a GIS platform and other mapping applications.
Orthophoto is used as a base layer in GIS programs. Ortho is made from aerial surveys (fixed wing or drone), or a satellite survey. An orthophoto is the rectified product of the raw acquired data and it has been corrected for differences in terrain height – this happens after flying.
Because it is highly accurate, companies use the imagery to measure and plan projects without having to go into the field. It’s used to digitize new or update land features like roads or changes in river systems. Forestry uses ortho to calculate the number of hectares cultivated the previous year and decide where to cut next year
Ortho rectified imagery is a valuable source of data for any project involving land use and planning.
Stereo Photography & Aerial Triangulation
Tarin’s aerial surveys are flown with a minimum 60% forward and 30% side overlap. This ensures that all of the imagery has full stereo capabilities. We supply the raw imagery and aerial triangulation results for incorporation into the most commonly used 3D viewing or softcopy photogrammetry environments. Using the raw imagery, people can map in 3D. This is used in wetland mapping or for mining. Looking at the data in 3D lets you accurately map roads, wetlands, water systems, building footprints and more.
2 . Satellite Imagery
High resolution satellite imagery is a valuable, economical product for many organizations. It is used for large area reconnaissance and smaller scale mapping projects.
A common question is, “What is the difference between free satellite imagery and paid services?” The difference is quality and accuracy. For example, the data on Google Earth is georeferenced, but not ortho rectified. So, if you use this data to plan, you could be off up to +/- 15m. Companies like Tarin can sell the data seen on Google Earth. If a client provides a scene, we supply that scene orthorectified, therefore, accuracy can be assured.
Tarin has access to a variety of high-resolution satellite imagery, from 5.0-meter RapidEye and 1.5 meter SPOT, to 0.6 meter QuickBird and 0.3-0.5 meter WorldView, and 0.5 meter Pleiades. These images are available in Panchromatic, False Color Infra-Red, and Pansharped Color. Tarin can provide archived data or task new acquisition.
The entire Western Canadian Sedimentary Basin is updated annually with new 1.5-meter Color SPOT satellite imagery, which is a valuable, economical product for large area reconnaissance, as well as, smaller scale mapping projects up to a scale of 1:5,000.
3. Elevation Data
Elevation data is a collection of points that have an elevation assigned to them, which can be used to visualize a project in 3D. For ease of use, the data is often converted to a surface representation frequently referred to as a DEM or DTM, which stands for Digital Elevation or Terrain Model. Simply put, it is a representation of the topographical surface of the earth.
Elevation Data used for:
Watershed analysis
Precision Farming and Agriculture
Archaeology
Infrastructure and Construction
Flight simulations
Emergency and relief planning
Airflow and Water flow predictions
Sight-line analysis
Rectification of orthophoto imagery
4. LiDAR
LiDAR (Light Detection And Ranging) is a non-traditional, cost effective method for obtaining very accurate and highly detailed topographic information. LiDAR data is fully digital and can be processed to provide diverse and highly detailed elevation products for bare earth surface and the features that protrude above the surface, like vegetation and man-made structures. Merging this data with current orthophoto imagery can provide a very accurate and detailed visual representation of the type of land cover within a project area.
Who uses LiDAR and for what?
LiDAR is used to aid in land use planning, as well as, engineering or seismic exploration. Just like imagery, it gives you a look at the ground without having to send someone out. You can make measurements of stockpiles, help decide what type of equipment will be needed, or where you should design a new road. Recently, LiDAR is responsible for discovering hidden Roman roads in England and a massive ancient city in Guatemala
At Tarin, extensive archived LiDAR data is available for most of Alberta and NE British Columbia. We also facilitate the acquisition of new data every year on a proprietary basis. While much of the data is available for “off the shelf” delivery via our Spatial Data Store and through our Subscription Services, please check the Coverage Map or contact orderdesk@tarin.ca for more information.