1. A system for three-dimensional vector extraction from remotely sensed imagery of the earth's surface, comprising: a vector extraction engine stored and operating on a workstation computer; wherein the vector extraction engine: builds a cost raster; builds a plurality of digital surface model rasters based at least in part on the cost raster; combines the rasters to form a new three-dimensional cost raster; identifies image features in at least one of the rasters; computes instantaneous values for the identified features; calculates a vector based at least in part on the instantaneous values; and projects the vector onto the new three-dimensional raster.