[Map] question about its basic 2d map structure~

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Hi all

I have some questions about the 2d map built by the map_server from the Nav_msgs::Occupancy Grid. There are few points unclear.

a)could I assume the origin of the map represent the (0,0) point, the lower-left corner of the 2d map?

b)could I assume that map.info.width contains the information of size of ENTIRE map?

c) could I assume the resolution is in meter/cell?

***Occupancy grid structure*:**
# This represents a 2-D grid map, in which each cell represents the probability of
# occupancy.


Header header 

#MetaData for the map
MapMetaData info

# The map data, in row-major order, starting with (0,0).  Occupancy
# probabilities are in the range [0,100].  Unknown is -1.
int8[] data

--------------------------------
***MapMetaData structure***
# This hold basic information about the characterists of the OccupancyGrid

# The time at which the map was loaded
time map_load_time
# The map resolution [m/cell]
float32 resolution
# Map width [cells]
uint32 width
# Map height [cells]
uint32 height
# The origin of the map [m, m, rad].  This is the real-world pose of the
# cell (0,0) in the map.
geometry_msgs/Pose origin