DTM ESTIMATION METHOD, DTM ESTIMATION PROGRAM, DTM ESTIMATION DEVICE, AND METHOD FOR CREATING 3-DIMENSIONAL BUILDING MODEL, AS WELL AS REGION EXTRACTION METHOD, REGION EXTRACTION PROGRAM, AND REGION EXTRACTION DEVICE

In relation to DTM estimation, pixels in which no data is present within a unit grid in a predetermined range are linked and a river region is extracted

a first maximum allowable slope value (e.g., 3 degrees) is set and a provisional DTM is estimated for data excluding the river region

a localized slope is calculated from the estimated DTM

and when the slope exceeds a predetermined value, a second maximum allowable slope value (e.g., 4.5 degrees) greater than the first maximum allowable slope value is set, and the DTM is estimated again. In relation to region extraction, when a building region is extracted on the basis of data such as an aerial photograph, a plurality of different discretization widths are set

and for each discretization width, the brightness values of the data are discretized into a plurality of values that have been discretely set using the discretization width. Also, in a discretized image obtained by discretization, pixels having identical values are linked, and a region having a shape similar to that of a rectangle is extracted as a candidate building region. Then, from among a plurality of region groups extracted for each different discretization width, a region having a shape that is most similar to that of a rectangle is used as the building region.