Polygon inflated
Geometric functions polygon inflated
- polygon_iXd(polygon_data_item, inflatesize)
- polygon_iXhv(polygon_data_item, inflatesize)
These functions result in inflated versions of an original polygon_data_item.
There are different ways of inflating polygons related to how angles are treated.
Multiple functions are implemented, the figure shows 4 of these functions. See the differences in how the angles are rounded off.
X represents a user defined degree of roundness, which can be 4, 8 or 16.
The suffix 'd' or 'hv' is used for the kernel; diagonal (diamond shaped) or horizontal-vertical (square shaped).
For these inflations the Minkowski sum method is used.
The inflatesize parameter indicates with how many units in the coordinate system used the original polygon is inflated.
- attribute polygon_data_item and with an ipoint or spoint value type.
- parameter inflatesize with float64 value type.
- The composition type of the polygon_data_item needs to be polygon.
- The order of the points in the polygon_data_item needs to be clockwise for exterior bounds and counter clockwise for holes in polygons (right-hand-rule).
- The current implementation of these functions request coordinate values to be less than 67.108.864. Convert detailed coordinates (e.g. in mm) to cm/dm if your coordinate values exceed this number.
These functions result in problems for (integer) coordinates larger than 2^25 (after translation where the first point is moved to (0, 0)). If your integer coordinates for instance represent mm, 2^25[mm] = about 33 [km]. The reason is that for calculating intersections, products of coordinates are calculated and casted to float64 with a 53 bits mantissa (in the development/test environment of boost::polygon these were float80 values with a 64 bits mantissa). We advise to keep the size of your integer coordinates for polygons limited and for instance do not use a mm precision for country borders (meter or kilometer might be sufficient).
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attribute<ipoint> building_inflated_4D75 (polygon, source/bld) := polygon_i4D(bld/border, 75);
// inflates building borders with 75 units in the coordinate system
// angles are rounded off with 4 points per angle
// inflates using a diagonal kernel (diamond shaped).
attribute<ipoint> building_inflated_i_8D75 (polygon, source/bld) := polygon_i8D(bld/border, 75);
// inflates building borders with 75 units in the coordinate system
// angles are rounded off with 8 points per angle.
// inflates using a diagonal kernel (diamond shaped).
attribute<ipoint> building_inflated_i_16D75 (polygon, source/bld) := polygon_i16D(bld/border, 75);
// inflates building borders with 75 units in the coordinate system
// angles are rounded off with 16 points per angle.
// inflates using a diagonal kernel (diamond shaped).
attribute<ipoint> building_inflated_4HV75 (polygon, source/bld) := polygon_i4HV(bld/border, 75d);
// inflates building borders with 75 units in the coordinate system
// angles are rounded off with 4 points per angle
// inflates using a horizonal-vertical kernel (square shaped).
