System and method for approximating cartographic projections by linear transformation

A computing device comprising:

• processing units including (i) a central processing unit (CPU) and (ii) a graphics processing unit (GPU),
• a tangible computer-readable memory storing thereon instructions that, when executed on the processing units, cause the processing units to:
• (i) render 3D geometry of a geographic area according to a selected perspective of a virtual camera in a 3D coordinate system,
• (ii) receive a map element, parameterized in a 2D coordinate system, to be applied to the 3D geometry,
• (iii) determine an approximate distance between the virtual camera and the 3D geometry, and
• (iv) select a degree of precision for transformation of coordinates between the 2D coordinate system and the 3D coordinate system based on the approximate distance, including:
• compare the determined distance to a threshold value,
• select a linear transformation between the 2D coordinate system and the 3D coordinate when the approximate distance is smaller than the threshold value, including:
• (a) concatenate, using a central processing unit (CPU) that supports double precision operations, a matrix chain to generate a single matrix for transforming coordinates between the 2D coordinate system and the 3D coordinates, wherein the matrix chain includes a first matrix to transform coordinates between the 2D coordinate system of the map element and a global 2D geographic coordinate system, a second matrix to transform coordinates between the global 2D geographic coordinate system and the 3D coordinate system, and a third matrix to transform coordinates between the 3D coordinate system and an eye relative coordinate system, and (b) carry out calculations in single precision on a graphics processing unit (GPU) that does not support double precision calculations, and
• select a non-linear transformation between the 2D coordinate system and the 3D coordinate system when the approximate distance is larger than the threshold value,
• (v) transform the map element to the 3D coordinate system according to the selected degree of precision;
• and
• (vi) render the map element in accordance with the transformation to the 3D coordinate system using 3D geometry map data in order to improve mapping applications by providing 3D geometry interactive scenery on a mapping display.

A method in a computing system for transforming points from a 2D coordinate system in which map data describes a geographic projection onto a plane to a 3D coordinate system in which 3D geometry of a geographic area is defined, the method comprising:

• receiving an indication of a position of a virtual camera in the 3D coordinate system, wherein the 3D geometry is rendered according to the indicated position, and wherein the position corresponds to approximate distance d between the virtual camera and a target point in the 3D geometry;
• and
• transforming the points from the 2D coordinate system to the 3D coordinate system, including:
• applying a curvature factor to account for the curvature of the Earth when the distance d is greater than a threshold value, including applying a non-linear transformation between the 2D coordinate system and the 3D coordinate system and
• not applying the curvature factor when the distance d is less than a threshold value, including:
• concatenating, using a central processing unit (CPU) that supports double precision operations, a matrix chain to generate a single matrix for transforming coordinates between the 2D coordinate system and the 3D coordinates, wherein the matrix chain includes (a) a first matrix to transform coordinates between the 2D coordinate system of the points and a global 2D geographic coordinate system, (b) a second matrix to transform coordinates between the global 2D geographic coordinate system and the 3D coordinate system, and (c) a third matrix to transform coordinates between the 3D coordinate system and an eye relative coordinate system, and
• carrying out calculations in single precision on a graphics processing unit (GPU) that does not support double precision calculations;
• and
• rendering the points in accordance with the determined transformation data in order to improve mapping applications by providing 3D geometry interactive scenery on a mapping display.