Computing contour map using topological cases and classifier cases

A method for use with a computing device, the method comprising:

• receiving raster data including a plurality of raster data values;
• obtaining classifier grid data including a plurality of classification values selected from among two or more classes;
• generating a contour map at least in part by:
• for each of the classes, generating a set of contour segments connecting respective pairs of grid locations included in the raster data, wherein generating the set of contour segments includes:
• computing respective topological cases of a plurality of cells of a superimposed grid, wherein:
• the superimposed grid includes a plurality of cells of the raster data that are associated with respective classification values included in the classifier grid data;
• and
• for each of the cells of the superimposed grid, the corresponding topological case indicates which of the raster data values included in the cell are greater than a current contour level;
• computing respective classifier cases of the cells of the superimposed grid, wherein, for each of the cells of the superimposed grid, the corresponding classifier case includes four Boolean flags that indicate which of four neighboring-cell classification values are equal to the classification value of the cell;
• and
• computing the contour segments based at least in part on the topological cases and classifier cases of the cells;
• combining the contour segments into a plurality of contours;
• and
• computing the contour map as a visual representation of the plurality of contours;
• and
• outputting the contour map for display at a display device.

A computing device comprising:

• one or more processing devices configured to:
• receive raster data including a plurality of raster data values;
• obtain classifier grid data including a plurality of classification values selected from among two or more classes;
• add a padding value border to the classifier grid data;
• generate a contour map at least in part by:
• computing a superimposed grid in which the classifier grid data is offset from the raster data by half a pixel along both a horizontal axis and a vertical axis, wherein:
• the superimposed grid includes a plurality of cells of the raster data that are associated with respective classification values included in the classifier grid data;
• and
• each of the cells of the superimposed grid has a height of two raster data values and a width of two raster data values;
• for each of the classes, generating a set of contour segments connecting respective pairs of grid locations included in the raster data, wherein generating the set of contour segments includes:
• computing respective topological cases of a plurality of cells of the superimposed grid, wherein, for each of the cells of the superimposed grid, the corresponding topological case indicates which of the raster data values included in the cell are greater than a current contour level;
• computing respective classifier cases of the cells of the superimposed grid wherein, for each of the cells, the corresponding classifier case includes four Boolean flags that indicate which of four neighboring-cell classification values are equal to the classification value of the cell;
• and
• computing the contour segments based at least in part on the topological cases and classifier cases of the cells;
• combining the contour segments into a plurality of contours;
• and
• computing the contour map as a visual representation of the plurality of contours;
• and
• output the contour map for display at a display device.