URSIM: Unique Region for Sketch map Interpretation and Matching (previously: Sketch Map Matching algorithms)

This programm is based from this paper to match sketch maps to equivalent metric maps. A previous method on this topic is also implemented in this repo (paper available here).

If you use this, please cite the URSIM method:

@article{Mielle_2019, 
	title={URSIM: Unique Regions for Sketch Map Interpretation and Matching}, 
	volume={8}, 
	ISSN={2218-6581}, 
	url={http://dx.doi.org/10.3390/robotics8020043}, 
	DOI={10.3390/robotics8020043}, 
	number={2}, 
	journal={Robotics}, 
	publisher={MDPI AG}, 
	author={Mielle, Malcolm and Magnusson, Martin and Lilienthal, Achim}, 
	year={2019}, 
	month={Jun}, 
	pages={43}}

and the previous study:

@inproceedings{mielle_using_2016,
	title = {Using sketch-maps for robot navigation: Interpretation and matching},
	doi = {10.1109/SSRR.2016.7784307},
	shorttitle = {Using sketch-maps for robot navigation},
	abstract = {We present a study on sketch-map interpretation and sketch to robot map matching, where maps have nonuniform scale, different shapes or can be incomplete. For humans, sketch-maps are an intuitive way to communicate navigation information, which makes it interesting to use sketch-maps for human robot interaction; e.g., in emergency scenarios. To interpret the sketch-map, we propose to use a Voronoi diagram that is obtained from the distance image on which a thinning parameter is used to remove spurious branches. The diagram is extracted as a graph and an efficient error-tolerant graph matching algorithm is used to find correspondences, while keeping time and memory complexity low. A comparison against common algorithms for graph extraction shows that our method leads to twice as many good matches. For simple maps, our method gives 95\% good matches even for heavily distorted sketches, and for a more complex real-world map, up to 58\%. This paper is a first step toward using unconstrained sketch-maps in robot navigation.},
	eventtitle = {2016 {IEEE} International Symposium on Safety, Security, and Rescue Robotics ({SSRR})},
	pages = {252--257},
	booktitle = {2016 {IEEE} International Symposium on Safety, Security, and Rescue Robotics ({SSRR})},
	author = {Mielle, M. and Magnusson, M. and Lilienthal, A. J.},
	date = {2016-10},
	keywords = {Buildings, Junctions, Measurement, Navigation, Robot sensing systems, Shape},
	file = {IEEE Xplore Abstract Record:/home/malcolm/.zotero/zotero/qwx8o4io.default/zotero/storage/WEKPNXGB/7784307.html:text/html;IEEE Xplore Full Text PDF:/home/malcolm/.zotero/zotero/qwx8o4io.default/zotero/storage/H83R9TWF/Mielle et al. - 2016 - Using sketch-maps for robot navigation Interpreta.pdf:application/pdf}
}

Dependencies:

• Opencv3
• BetterGraph
• VoDiGrEx
• Edit distance
• RSI

Old README for previous method:

What is the Sketch Map Matching ?

The Sketch Maker is a method to interpret sketches i.e transcription from drawing to topological map

What are sketch maps ?

Drawing that represent an indoor places. They are often innacurate and simplified version of the real environment. You can see some in the folder Test/GraphDB/Sketches/KTH.

How do I use the Sketch Maker ?

The simplest way to use this package is to use this UI. You only have to draw the sketch and to give it the model to see the result :D.

To use the sketch maker you need to compile using cmake .. in a build directory and then make. Then install the package with sudo make install

What are the dependencies of Sketch Maker ?

Sketch maker is based on OpenCV (v : 2.4.9) and Boost.

Under fedora those are the command needed to install those packages :

dnf install git cmake
dnf install opencv-devel
dnf install qt4-devel
dnf install boost-devel

Under Ubuntu just :

sudo apt-get install git cmake
sudo apt-get install libopencv-dev 
sudo apt-get install libboost-all-dev

It also depends on:

• BetterGraph
• VoDiGrEx
• Edit distance

Install

git clone the repo.

Then :

mkdir build
cd build
cmake ..
make

For debugging

mkdir debug
cd debug
cmake -DCMAKE_BUILD_TYPE=Debug ..
make

Questions you might have

I don't like the build in interpretor what can I do ?

Well, you could code your own. Every interpretor is based out of two abstract classes :

• Thinker : first step of interpretation of the map. Sort of a preprocessing. I know, it's not the clearest name.

• PlaceExtractor : extract a GraphPlace from a GraphList.

• GraphMatcherBase : match and compare two Graphplaces.

And the non abstract class :

• LineFollower. The line follower is the class that extract the graph from an image.

For now, as intersection types in the GraphLine, T crossing, X crossing and N (meaning any other number) crossing exist. The graph structure is stored as a Boost Graph. See this for more information on the library. In particular one can use a lot of alogorithm like Dikjstra or Astar. The graph extracted from the lines is a

typedef boost::adjacency_list<boost::listS, boost::listS, boost::undirectedS, topologicalmap::Intersection_Graph, boost::edge_weight_t, boost::no_property >

meaning that it's stored in vectors, it is undirected and the vertices are a Intersection_Graph object defined as :

struct Intersection_Graph{
	std::string type;
	cv::Mat mat;
	cv::Point2i point;
	int index;
};

For now, the edge got all the same weight but in the future an approximate distance might be added.

For the comparison a GraphPlace is used :

typedef boost::adjacency_list<boost::listS, boost::listS, boost::undirectedS, graphmatch::Place, graphmatch::Gateway_struct, boost::no_property > Graph_places;

It's stored in lists, it's undirected, the vertices are Place objects and the Edges and Gateway_struct.

Place is an important object since they include an element named Keypoint which is used for the comparison. It's easy to had new types of Place and different comparison methods thanks to their Keypoint elements.

The Keypoint class :

Create the Keypoints

The Keypoint class is the object used for every comparison between two graph places. It's fairly easy to had new type of keypoints and comparison method. Just follow those steps :

1. Create every class of vertex you want to use for the comparison algorithm. Every of those class must inheritate from Keypoint and reimplement the following functions :

   • Keypoint(const std::string& typet) : type(typet){} Keypoint() : type("notype"){ std::cout << "Using the constructor" << std::endl;}

   • //@brief return a one character representing the type virtual std::string getID() const

   • ///@brief return true if the graphmatch::VertexPlace is of *this type virtual bool isOfType(const graphmatch::VertexPlace& v)

   • ///@brief return a pointer to an element on this class if the vertex is determine to be of this class. virtual Keypoint* compare(const graphmatch::VertexPlace& v, const graphmatch::Graph_places& gp) const{

   • virtual Keypoint* makePointer() const

   • virtual cv::Scalar getColor(int channel) const

For every keypoint you want to use :

• Your keypoint types must define the whole space.

• No keypoint should return the same character ID

See JunctionAndDeadEnds.hpp for an example.

Create a Place extractor :

You then have to implement a class that inheritate from PlaceExtractorBase. The function that extract a GraphPlace with your keypoints from a GraphList is name extract and is the only function that you must implement. The results are stored in graphmatch::GraphPlace _graph.

Every PlaceExtractor should be associated with a class inheritating from AllKeypoints. The only function one would need to implement is init_all_types_of_keypoints() were you need to add a list of Keypoint pointers to the _all_types_of_keypoints attribute of the class.

This class is used during the place extraction. Mainly, the function compare is used to see if one of the Keypoint stored in the onject inheritating from AllKeypoints correspond to the vertex inputed. If yes, a new pointer to an Object of the same Keypoint is return and must be stored in the input vertex. If non, a pointer to NULL is returned.

Now all this must seem complicated and a lot of work but If you only want to use an existing extraction method with your custom keypoints, it's really easy. All you have to doo is declare your keypoints and then change the AllKeypoints element in the place extractor you want to use. Simple as that ! :)

How does the interpretor works ?

For now the interpretation is made like this :

• First, the drawing is processed and the voronoi lines are extracted. This result in an image where the voronoi lines are white and the rest is black. There is multiple ways to obtain the voronoi line but the most efficient one (as in fast and accurate) is to use LaPlace on a trimmed version of a map of all the distance, with a downsampling coef of 1. Like this it's stil possible to draw in Real Time. See next section for more detail.

• Second, the line are processed using a slightly modified version of the Algorithm presented in Orit BARUCH - Line Thinning by line following - Pattern Recognition Letters 8 1988. By line following we detect the intersections and create a Topological map out of this. The main advantage of this technique is that the algorithm can be reused with any given graph. So if the user want to draw a path it can be interpreted. It's not only a matter of drawing walls.

The main advantage of doing all of this graphically is the possibility to process a picture of a map. Just by having a camera, a picture of sketch could be sent to the robot for interpretation. The intrepretation is entirerly interface independant.

• Then the places in the map are extracted by PlaceExtractor and converted to a GraphPlace.

• Finally a GraphMatcher compare to SketchMap to figure out the best matching.

How are the voronoi lines extracted ?

I use the Voronoi extraction from VoDiGrEx. Although, several method to extract Voronoi Lines exists as the EVG Thin, I found this method to be more efficient and faster, for all the reasons listed in this blog post. Plus, it does not remove some of the lines that are removed by EVG.

If you have a perfect building map :

By perfect, we consider all building map with straight corridors. The method is as such :

• Compute the pixel distance of every point in the image.

• Convolve the distance image with either [0, 1, 0 ; 1 , -4, 1 ; 0, 1, 1] or [1, 1, 1 ; 1 , -8, 1 ; 1, 1, 1].

• The negative values in the resulting image correspond to local maximas in the distance image and are the voronoi lines.

If the map is a sketch :

• Compute the pixel distance of every point in the image.

• Blur it using a 5*5 gaussian kernel and downsample it by removing every even rows and columns. This step is needed to remove all the weak maximas.

• Convolve the distance image with either [0, 1, 0 ; 1 , -4, 1 ; 0, 1, 1] or [1, 1, 1 ; 1 , -8, 1 ; 1, 1, 1].

• Keep the 70% most negative value of the image (the strong maximas of the distance image).

This is the same method as presented in Parameter controlled skeletonization of three dimensional objects by Gagvani. Only, in his version the "thinness parameter" (which basically is our percentage) is manually chosen while here, we systematically use 70%.