Efficient graphical element top surface rendering in digital map

A non-transitory computer readable storage medium having instructions encoded thereon that, when executed by one or more processors, cause the one or more processors to:

• receive, 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, from the mapping server, non-flat terrain data describing elevation values corresponding to ground points on the map tile;
• render the map tile, the rendering comprising:
• selecting a sample point on the map feature, wherein the sample point is a ground point within the geometric base represented by the set of vertices;
• determining a sample ground elevation value of the sample point using the non-flat terrain data;
• determining a top surface elevation value of the map feature based on a sum of the sample ground elevation value and the height value;
• determining a set of vertex ground points corresponding to the set of vertices on the map tile;
• determining vertex ground elevation values of the set of vertex ground points corresponding to the set of vertices using the non-flat terrain data, 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;
• determining vertex height values of the set of vertices using the vertex ground elevation values and the top surface elevation value;
• and
• rendering 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 a top surface shown as a graphical element of the map feature having an elevation corresponding to a sum of the sample ground 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 the rendered map tile on an electronic display.

A system, comprising:

• one or more processors;
• and
• a non-transitory computer-readable storage medium comprising instructions that, when executed by the one or more processors, cause the one or more processors to perform operations, the instructions comprising instructions to:
• receive, 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, from the mapping server, non-flat terrain data describing elevation values corresponding to ground points on the map tile;
• render the map tile, the rendering comprising:
• selecting a sample point on the map feature, wherein the sample point is a ground point within the geometric base represented by the set of vertices;
• determining a sample ground elevation value of the sample point using the non-flat terrain data;
• determining a top surface elevation value of the map feature based on a sum of the sample ground elevation value and the height value;
• determining a set of vertex ground points corresponding to the set of vertices on the map tile;
• determining vertex ground elevation values of the set of vertex ground points corresponding to the set of vertices using the non-flat terrain data, 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;
• determining vertex height values of the set of vertices using the vertex ground elevation values and the top surface elevation value;
• and
• rendering 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 a top surface shown as a graphical element of the map feature having an elevation corresponding to a sum of the sample ground 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 the rendered map tile on an electronic display.