# Gslam /tf coordinate problems

So I am using gmapping slam_gmapping base:=scan with rosstage and things are going nicely. (I am using rviz). There are two questions which I am sure are nooby, but I can't find the answers anywhere.

(I am putting the frames inside () because I am not sure how else to signify the difference)

1) The first problem is /tf (base_footprint) and /tf (base_link) and /tf (base_laser_link) all give me a believable value of 7.9, .83 (I let the robot move in a straight line for a little bit). However, if I am reading the gslam tutorial correctly, I should be using /tf (/map) for the transform in the map space. It is giving me the following values -0.004988, -0.01188 The size of the map is 4000,4000 and the resolution is .05. But I am not sure how to tranform these values into real world values.

2) I am hoping that the answer for the first question will answer the second one, but I am given an occupancy grid for a map that is 4000 X 4000 I need to be able to translate Slam coordinates (or real world coordinates) into this discrete space. Is this the same transfer function as the /tf(/map)?

Thank

~BM