Control Points for Landsat 7 Imagery

Description

Control Points for Landsat 7 Imagery consist of a set of georeferenced points that are readily identifiable at various map scales. Along with the Landsat 7 orthoimages, they comprise one of the two components of the GeoBase Data Alignment Layer (GDAL).

The control points were used for the geometric correction of Landsat 7 satellite imagery. They can also be used to correct vector data and for simultaneously displaying data from several sources prepared at different scales or resolutions.

The control data come from different sources; selection priority is given to the most accurate sources. The normal ranking in decreasing order is: Updated Road Network vector data, provincial vector data, accurate National Topographic Data Base (NTDB) data, federal aerotriangulation data, and other sources. Accuracy is assessed for each control point. The control data, which have been extracted from the sources indicated above, can be comprised of vector data from road intersections or centres of gravity of lakes and islands. In some cases, the intersection with the centre line of a river represented as a surface may have been used.

Each control point is unique and its position is determined to simultaneously cover the greatest possible number of Landsat 7 images (location in areas of image overlap). Control points are distributed homogeneously within the image depending on specific sectors. The sectors are located around the image perimeter, in the image's areas of lowest and highest elevation, as well as the areas in which adjacent images overlap.

A map context is also associated with each control point (control point context). The intersections of linear topographic features (road, railway, watercourse, etc.) and the perimeters of lakes and islands are extracted in order to facilitate identification of control points. The reference entities result from vectorization of perceptible topographic features extracted from Landsat 7 source images.

The control points will cover the entire Canadian landmass. Control point availability is directly related to the production of Landsat 7 orthoimages, which began in 1999 and will be completed in spring 2005.

Documentation

For more details on Control Points for Landsat 7 Imagery standards and specifications, see Control Points for Landsat 7 Imagery, Product Specifications [pdf 178 KB].

Metadata

For a complete description of collection metadata, see the Control Points for Landsat 7 Imagery, Collection Metadata.

Use and Restrictions

All distributed Control Points datasets should be accessed and used relatively to the GeoBase Unrestricted Use Licence Agreement.

Data Discrepancies

This product is subject to Discrepancies processing provided by the Centre for Topographic Information from Natural Resources Canada. A discrepancy is defined as any deviation from the product's Standards and Specifications. To explore the status of discrepencies related to National Road Network datasets, see the Discrepancies Web Site from the Centre for topographic Information.

Data Format

Control Points datafiles are available in both GML (Geography Markup Language) and ESRI Shapefiles.

Free Data Viewer

As a service to GeoBase users we are providing links to some free viewers. However, GeoBase does not endorse and does not provide any kind of support for any of these viewers.