Mapping System

The Sensor Hub has a low-definition digital map of its operating area. That map is a directed graph of intersections. The files system on the SD card is organized at the original PC MS-DOS system: file names of up to 8 characters, a dot, and an extension of up to three characters.

The master files is named MAP_DEFS.TXT It may look like this:

47.758949, -122.190746, UWB_CAMP.TXT

47.6213 , -122.3509 , SEATTCEN.TXT

47.662 , -122.115 , MARYMOOE.TXT

47.660 , -122.185 , BRIDLETR.TXT

47.760854, -122.190033, UWB_SCCR.TXT

49, 8, CARLA.TXT

The first two numbers are the latitude and longitude of the origin of the map file. The third item is the name of the file. When the robot powers up, it will acquire a GPS fix for its present position. It will find the closest latitude and longitude to its position and load that file.

For instance, the first few entries of MARYMOOE.TXT are

 -775855,  -78948, 1 ,  END,  END,  END,  1, 1, 1, 1
 -598367,   16679, 0 ,   2 ,  END,  END,  1, 1, 1, 1
 -426121,  137882, 3 ,   17,   19,  END,  1, 1, 1, 1
 -345240,  149001, 4 ,   18,  END,  END,  1, 1, 1, 1
 -216431,  154561, 18,   15,  END,  END,  1, 1, 1, 1
 -34449,   174576, 4 ,   6 ,   14,  END,  1, 1, 1, 1
 89118,    116792, 5 ,   7 ,   13,  END,  1, 1, 1, 1
 148281,   165680, 6 ,   8 ,   12,  END,  1, 1, 1, 1

Each line corresponds to one of the numbered intersections (nodes) in the figure, starting at 0 and increasing by 1. The fist number is the distance north from the origin in millimeters (or distance south for a negative number). The second number is the distance east in mm if positive or distance west if negative. The third, forth, fifth and sixth numbers are the nodes connected to the present node, or "END" if none. An intersection of more than four ways can be handled by introducing a helper node at the same location.

The last four numbers are the relative costs of the paths linking the nodes. Path planning is done with A*, which makes the assumption that the distance between nodes is Euclidean. If this is not the case, due to road curvature or speed restriction, the multiplier should be modified.