Terrain Contour Matching ( Tercom ) Essay
709 Words Dec 2nd, 2015 3 Pages
TERCOM is an algorithm that analyses the mean absolute distance by matching the distance between the map depth and the measured depth, as explained by (Carreno, 2010). With TERCOM, the measurements from a certain profile along the trajectory are processed in batch, but it may also be run recursively. The method indirectly assumes constant position offsets from the INS position each time it is started.
Point Mass Filter (PMF)
PMF is a calculation that determines the position probability density function (PDF), as said by (N. Bergman, 1999). The point mass filter estimator the priori position distributions together with the error models of the depth measurements and the map to produce a posteriori probability density function, which is used for the position by means of Bayes’ theorem. (Golden, 1980) Once a PDF for the position has been generated, an estimate of the position can be found as the mean, the median or the highest point. In addition the covariance can also be computed from the PDF, this implies that the PMF has a check for convergence, which TERCOM does not have. On the other hand, it is computationally more intensive and requires knowledge of the errors that can occur in the sensors and the DTM.
The PMF can be run both recursively, processing single measurements, or as a batch processing algorithm, processing several measurements at the time. Batch processing is for MBE or 3D sonar.
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