Extract specific Data from topic

edit

Hello there,

I have a node in ros publshing data of type Measurement2 which is used for RN Sensors. The problem wit the Datatype is that it publishes several different Values like you can see here:

header: 
  seq: 36
 stamp: 
    secs: 1531906243
    nsecs:  20823955
  frame_id: "wifi_adapter"
device_name: "simulated"
device_designation: "wifi_adapter"
classification: "W"
values: 
  - 
    sensor: "Elrob-RN-1"
    source: "wifi signal strength"
    type: "wifi signal strength"
    value: [-30.0]
    unit: "dBm"
    min: 0.0
    avg: 0.0
    max: 0.0
    alert_level: 0
    alert_explanation: ''
    substance: []
    info: "Freq. 2.457 GHz mode: Master address: 08:EA:44:7A:FA:55 quality: 70/70 signal: -30.0"

I want to filter out the value of the signal and frequency from the broadcasted topic and then show it in rviz at the current position of my robot but I havent found a way yet how to extract the data and modify it so I can show it colorcoded on the created map in rviz

edit: thanks for editing the post to look better I somehow didnt get it to look straight

EDIT1:

My setup is a roboter with Laserscanners and RGBD Cameras to create a 2D and 3D map of its surroundings. Now I have to make something like a heatmap to show where strong signals occur on this generated maps. For this I need to extract specific Data from the topicoutput shown above. Especially i need the signalstrength and frequency data from the whole dataset.