Precision Geocor System

Turning Images into Maps

As the final program run in the ITRES Standard Processing chain, Geocor geometrically corrects sensor image data by mapping it onto a chosen coordinate system (e.g. UTM).

Geocor brings together three data streams acquired during sensor operation:

  1. Image data from an ITRES sensor
  2. Attitude (roll, pitch, heading) data
  3. Position (X, Y, Z) data

The latter two data streams are referred to collectively as navigation data and are provided by a precision GPS/IMU. Geocor also incorporates Lidar or Ifsar Digital Elevation Models (DEMs) and sensor alignment corrections to improve image positional accuracy.

Bundle Adjustment Input

Multiple sensors (imaging sensor, GPS antenna, & IMU) are installed in the aircraft. Installation-related linear and angular offsets between each sensor are measured and corrected for using pbsbund, a program run once on imagery acquired over an established geometric calibration site. Pbsbund generates a set of coefficients used to correct the navigation (attitude & position) data from future datasets, which are then input to Geocor. Doing so results in substantial positional accuracy improvement to the output imagery without the use of project-specific GCPs and tie points.

Geocor Sensor Compatibility

Geocor works with data from all ITRES sensors (CASI, SASI, MASI, TASI and TABI).

Georeferencing Accuracy

Formal assessments of the georeferencing accuracy of datasets from ITRES sensors processed using Geocor have been undertaken by independent third parties, including NOAA. Typically these show RMS errors of +/- 1 pixel for 1 m pixels when incorporating a Lidar-based DEM and bundle adjustment. The accuracy and resolution of the DEM and quality of the navigation data often provide the largest influence on positional accuracy.

Geocor Specifics

  • Imagery 16-bit, Unsigned Integer, BIP format (native), BSQ, BIL (ENVI, PCI & ERDAS Imagine compatible)
  • (For thermal imagery) 32-bit float or 16 bit signed, BIP format (native), BSQ, BIL (ENVI, PCI * ERDAS Imagine-compatible)
  • Minimize nadir option during mosaicking to reduce off-nadir view
    angle effects
  • Supports UTM (native), 3TM, British National Grid, and State Plane Coordinate systems, other coordinate systems are available
  • Via formnav program, supports map projections other than Transverse Mercator (native) and datums other than NAD83 or WGS84
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