12. Generate the Map

Mapping

So far, you’ve coded the Occupancy Grid Mapping algorithm in C++ and generated an occupancy grid map 2D vector. Now, you'll code a visualization function that will loop through each cell. Then, you'll differentiate between occupied, free, and unknown cells depending on their log odds value. And, finally, you'll plot each cell on a graph to generate the map.

Udacity Workspace

For this quiz, you will need to use the Udacity Workspace . So, move to the next concept, enable the GPU, and Go To Desktop. Then follow these instructions:

Clone the Lab from GitHub 

$ cd /home/workspace/
$ git clone https://github.com/udacity/RoboND-OccupancyGridMappingAlgorithm

Next, edit main.cpp

Code the visualization function which will plot the state of each grid cell using the matplotlib python library 

void visualization()
{
    //TODO: Initialize a plot named Map of size 300x150

    //TODO: Loop over the log odds values of the cells and plot each cell state. 
    //Unkown state: green color, occupied state: black color, and free state: red color 

    //TODO: Save the image and close the plot 
}

Here are some helpful commands you can use to generate plots with the matplotlib library:

  • Set Title : plt::title("Your Title");
  • Set Limits : plt::xlim(x-axis lower limit, x-axis upper limit );
  • Plot Data : plt::plot({ x-value }, { y-value }, "Color and Shape");
  • Save Plot : plt::save("File name and directory") ;
  • Close Plot : plt::clf() ;

Check out this link for more information on the matplotlib C++ library. For information regarding the plot color and shape refer to the LineSpec and LineColor section of the MATLAB documentation.

Then, compile the program 

$ cd RoboND-OccupancyGridMappingAlgorithm/
$ rm -rf Images/* #Delete the folder content and not the folder itself!
$ g++ main.cpp -o app -std=c++11 -I/usr/include/python2.7 -lpython2.7

Finally run the program 

$ ./app

If you get a warning regarding the matplotlib library, just ignore it.

Now, wait for the program to generate the map and store it in the /home/workspace/RoboND-OccupancyGridMappingAlgorithm/Images directory!

Generated Map

Map Legend

  • Green: Unkown/Undiscovered zone
  • Red: Free zone
  • Black: Occupied zone

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