Given an image, is it possible to manually draw a graph over it? For example, taking the following image:

enter image description here

I want to manually pick the vertices and draw the edges in a "Paint-like" manner to get, for example,

enter image description here

By manually I mean literally using the mouse to select the vertices.

Any ideas?

Note: This is the "easy" solution to this question, where I intend to build an automatic image processing program. For now, however, a manual solution would suffice.

  • $\begingroup$ Have a look at LocatorPane. $\endgroup$ – Carl Lange Feb 10 '20 at 21:27

enter image description here

There are many ways to do this, modifying, improving my method or doing a completely different thing. My goal here is to show a very basic idea that should give you a start. LocatorPane and Manipulate give means of interactive addition/deletion and dragging of points in 2D plane. The problem is how to add an edge -- there has to be interaction between 2 points. The idea used here is the following:

  • Assume empty initial list of edges
  • Trigger for making an edge is when 2 points become close enough
  • Accumulate such edges and build a graph
  • Jump through various hoops for proper sorting, duplicate deletion, etc.

Let's start from importing image:


defining a function:


Note "Index" property usage, which important, because you need to build edges from indexes of points - not from point coordinates. Read docs on all these functions to understand how it works. r defines distance threshold between the points -- if you go under it an edge will be created. Here is an easy interactive app that uses above function to accumulate edges:


You are adding a point with CMD+CLICK action. Note there are many possible improvements. For instance, optimization for speed. Or "undo" action -- you cal also remove a point with CMD+CLICK action, but this will destroy the graph due to ordering and numbering issues, - so there is no undo for now -- up to you to make it. Cool thing about it is - the graph object is easy to get separately and compute with:

{g, MatrixPlot[AdjacencyMatrix[g]]}

enter image description here

Related Resources

Constructing and Manipulating Graphs


Also take a look at this legacy tool:

  • 2
    $\begingroup$ Very nice! When copying your code that starts with "Clear[edges]", it complains because "i" is not defined so "Show[i,g]" has a problem. Did I miss a piece of code that needs to be run? $\endgroup$ – Mark R Feb 11 '20 at 0:47
  • 1
    $\begingroup$ Thanks @MarkR, yes I added now definition of i, it is the image. $\endgroup$ – Vitaliy Kaurov Feb 11 '20 at 1:49
  • 1
    $\begingroup$ Thanks for including the image. I really like this. $\endgroup$ – Mark R Feb 11 '20 at 2:52
  • 2
    $\begingroup$ This is REALLY COOL, Vitaliy! Can you clarify how this is “connecting” the vertexes with the edges from just touching them together, though? I can’t readily tell, is it from the LocatorAutoCreate->True? $\endgroup$ – CA Trevillian Feb 11 '20 at 3:23
  • 1
    $\begingroup$ @VitaliyKaurov very cool stuff, thanks! $\endgroup$ – GenericAccountName Feb 14 '20 at 17:06

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.