an image appointment unit that receives user appointment of at least one position in a building existing within a single optical 2D image to designate the at least one position as part of a building region;

a polygon extraction unit adapted to utilize the single optical 2D image exclusively, to extract at least one pixel from pixels within the building region based on a result of discriminating a color of the pixels around the building region to compare whether the pixels are within a color variance of a predetermined discrimination threshold, to set the building region to include extracted pixels as a portion of an extracted building region, and to repeat the extract and set operations to expand the extracted building region with more extracted pixels, and then to extract plural polygon lines of the extracted building region; and

a structural analysis and integration unit adapted to utilize the polygon lines which were extracted by the polygon extraction unit using the signal optical image exclusively, to detect a boundary of the building region and lines inside the building region, and to compare between a shape of detected lines and a predetermined shape pattern of cross lines;

wherein the structural analysis and integration unit estimates the building region based on the compared shape of the detected lines in a case where the lines inside the building region correspond to any predetermined integration patterns, and terminates a process for integrating the building structure in a case where there exist no lines corresponding to any of the integration patterns, and

wherein the polygon extraction unit generates a vector of a polygon line of the extracted building region which was estimated by the structural analysis and integration unit.