Geospatial information creating system and geospatial information creating method

1. A geospatial information creating system for extracting a footprint of a house from an aerial photograph, comprising a processor for executing a program, a memory for storing data required for executing the program, and a storage unit for storing the aerial photograph, wherein the processor is configured to:

detect edges of an image based on a characteristic quantity of neighboring pixels in the aerial photograph stored in the storage unit;

extract an orientation of the house by analyzing directions of the detected edges;

generate a polygon of an outline of the house by using linear lines of the extracted orientation of the house;

receive specification of a position by an operator for the house to extract the footprint;

determine a house area by an extent covered by extracted edges by periodically extracting neighboring pixels more similar than a threshold before extraction of the edges; and

change the threshold by decreasing it, and extract again neighboring pixels more similar than the changed threshold in the case where the determined house area does not include the specified position.

2. The geospatial information creating system according to claim 1 , wherein the processor is further configured to:

determine straight line segments to which the detected edges fit;

define the orientation of the house based on angles of the determined straight line segments;

classify the determined straight line segments into those in the defined orientation of the house and those in a direction orthogonal thereto;

generate grids at positions at which the classified straight line segments exist; and

generate the polygon of the outline of the house according to the generated grids.

3. The geospatial information creating system according to claim 2 , wherein the processor is further configured to:

calculate a color spectrum in each grid cell segmented by the generated grids, and calculate a similarity index of neighboring grid cells based on the calculated color spectrum; and

merge grid cells having the calculated similarity index larger than a predetermined threshold to generate a rectilinear polygon patch corresponding to the footprint of the house surrounded by linear lines.

4. The geospatial information creating system according to claim 2 , wherein the processor is further configured to:

determine a first frequency of a position of the determined straight line segments which is weighted by a length of the determined straight line segments, and generate a grid line constructing the grid at a position having the first frequency larger than a predetermined threshold; and

calculate the first frequency so that the first frequency of a straight line segment close to the generated grid line is added to the first frequency of the generated grid line.

5. The geospatial information creating system according to claim 2 , wherein the processor is further configured to determine a second frequency of the angle of the determined straight line segments which is weighted by a length of the determined straight line segments, and define an angle high in the second frequency as the orientation of the house.

6. A geospatial information creating method for extracting a footprint of a house from an aerial photograph, the method being carried out by a computer system including a processor for executing a program, a memory for storing data required for executing the program, and a storage unit for storing the aerial photograph, the method comprising:

detecting edges of an image based on a characteristic quantity of neighboring pixels in the aerial photograph stored in the storage unit;

extracting an orientation of the house by analyzing directions of the detected edges;

generating a polygon of an outline of the house by using linear lines of the extracted orientation of the house;

receiving specification of a position by an operator for the house to extract the footprint;

determining a house area by an extent covered by extracted edges by periodically extract neighboring pixels more similar than a threshold before extraction of the edges; and

changing the threshold by decreasing it, and extracting again neighboring pixels more similar than the changed threshold in the case where the determined house area does not contain the specified position.

7. The geospatial information creating method according to claim 6 , further comprising:

determining straight line segments to which the detected edges fit;

defining the orientation of the house based on angles of the determined straight line segments;

classifying the determined straight line segments into those in the defined orientation of the house, and those in a direction orthogonal thereto;

generating grids at positions at which the classified straight line segments exist; and

generating the polygon of the outline of the house according to the generated grids.

8. The geospatial information creating method according to claim 7 , further comprising:

calculating a color spectrum in each grid cell segmented by the generated grids, and calculating a similarity index of neighboring grid cells based on the calculated color spectrum; and

merging grid cells having the calculated similarity index larger than a predetermined threshold to generate a rectilinear polygon patch corresponding to the footprint of the house surrounded by linear lines.

9. The geospatial information creating method according to claim 7 , further comprising:

determining a first frequency of a position of the determined straight line segments which is weighted by a length of the determined straight line segments, and generating a grid line constructing the grid at a position having the first frequency larger than a predetermined threshold; and

calculating the first frequency so that the first frequency of a straight line segment close to the generated grid line is added to the first frequency of the generated grid line.

10. The geospatial information creating method according to claim 7 , further comprising:

determining a second frequency of the angle of the determined straight line segments which is weighted by a length of the determined straight line segments, and

defining an angle high in the second frequency as the orientation of the house.