Efficient graphical element top surface rendering in digital map

A non-transitory computer-readable storage medium comprising instructions that, when executed by a computer processor, cause the processor to perform operations, the instructions comprising instructions to:

• receive, by a client device from a mapping server, a map tile representing a geographic region, the map tile associated with a map feature having a geometric base and a height value, wherein the geometric base is represented by a set of vertices on the map tile;
• receive, by a client device from a mapping server, map non-flat terrain data including elevation values for points on ground of the map tile;
• determine, by the client device, whether all vertices of the map feature are in on the map tile;
• responsive to determining all vertices of the map feature are in the map tile, render the map tile by a graphics processing unit (GPU) of the client device, the rendering comprising:
• select a sample point on the map feature based on the set of vertices;
• determine, by the GPU, a sample ground elevation value for the sample point using the map non-flat terrain data;
• determine a top surface elevation value of the map feature based on a sum of the sample ground elevation value and the height value;
• determine, by the GPU, vertex ground elevation values for respective vertices in the set of vertices using the map non-flat terrain data;
• determine vertex height values for respective vertices in the set of vertices using the vertex ground elevation values and the top surface elevation value, wherein at least one vertex ground elevation value is different from the sample ground elevation value due to non-flat terrain around the map feature;
• and
• render the map tile with the map feature using the vertex ground elevation values, and the vertex height values, wherein the map feature is rendered in three dimensions with the top surface shown as a graphical element of the map feature having an elevation corresponding to a sum of the sample elevation value and the height value, and each vertex corresponding to a vertical edge of the map feature extending between the top surface and ground;
• and
• display, by the client device, the rendered map tile on an electronic display of the client device.

A system, comprising:

• a computer processor;
• and
• a non-transitory computer-readable storage medium comprising instructions that, when executed by the computer processor, cause the processor to perform operations, the instructions comprising instructions to:
• receive, by a client device from a mapping server, a map tile representing a geographic region, the map tile associated with a map feature having a geometric base and a height value, wherein the geometric base is represented by a set of vertices on the map tile;
• receive, by a client device from a mapping server, map non-flat terrain data including elevation values for points on ground of the map tile;
• determine, by the client device, whether all vertices of the map feature are in the map tile;
• responsive to determining all vertices of the map feature are in the map tile, render the map tile by a graphics processing unit (GPU) of the client device, the rendering comprising:
• select a sample point on the map feature based on the set of vertices;
• determine, by the GPU, a sample ground elevation value for the sample point using the map non-flat terrain data;
• determine a top surface elevation value of the map feature based on a sum of the sample ground elevation value and the height value;
• determine, by the GPU, vertex ground elevation values for respective vertices in the set of vertices using the map non-flat terrain data;
• determine vertex height values for respective vertices in the set of vertices using the vertex ground elevation values and the top surface elevation value, wherein at least one vertex ground elevation value is different from the sample ground elevation value due to non-flat terrain around the map feature;
• and
• render the map tile with the map feature using the vertex ground elevation values, and the vertex height values, wherein the map feature is rendered in three dimensions with the top surface shown as a graphical element of the map feature having an elevation corresponding to a sum of the sample elevation value and the height value, and each vertex corresponding to a vertical edge of the map feature extending between the top surface and ground;
• and
• display, by the client device, the rendered map tile on an electronic display of the client device.