Understanding android.graphics.path and comparing android.graphics.path values

Question

I am working on an application in Android, wherein I have to get android.graphics.path values and compare them.

Consider the following images :

and

The first image shows a straight line and the generated Path value. Similarly, the second image,also shows a similar straight line, with a different Path value.

I'm unable to understand the value that is generated. Can anyone explain as to what exactly the generated values mean? Can I approximately take a wild guess about a path value from the screen coordinates?

Also, in my application, I would like to compare path values. The lines shown in the above figure are similar. And in my application, I would like to compare them and render them as same lines. And I'm not just going to compare lines, there'll be curves and all such drawable shapes. For comparison do I first have to normalize my path values (maybe calling getMatrix for my current canvas?), so as to have the same effect for different screen sizes?

There is one other way of comparison that will be much simpler,finding centroids of the paths of figures. Obviously lines will have a centroid at a different position compared to curves,etc. But this sort of comparison won't be so accurate. I wanted to store some value and then compare the generated path value to the stored value, along with comparing the centroids, so as to have a better accuracy. But for that, I need to understand the generated path values!

Please help or guide! Thanks! :-)

Edit:

The code that I'm using for converting my path values to String. My path values are stored in an ArrayList (called pointsToDraw ). Here's the code :

@Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                        synchronized(pointsToDraw){
                        for(Path path : pointsToDraw)
                        {
                            stringPoints.add(String.valueOf(path));
                        }
                        }
                        TextView b1Text = (TextView) findViewById(R.id.GText);
                        for(String s : stringPoints)
                        {
                            b1Text.setText(s);
                        }

            }

Answer 1

A Path object is an object that encapsulates a series of geometric paths. If you want to programmatically compare one path to another, then the place I think you have to start is to use PathMeasure on that Path object in order to pull out all of the co-ordinates. Using PathMeasure you can obtain a series of co-ordinates that the path follows, by supplying a distance argument.

PathMeasure

Then, in order to determine whether one given path is similar to another in terms of the size and its path along the screen, I would perhaps suggest using PathMeasure on them both and comparing the co-ordinates they produce given incremental distance arguments. Then use some comparison algorithm, which may be as simple as determining whether each set of compared co-ordinates are within a distance from each other (with relative starting co-ordinates taken into account).

So I can't help with the algorithm you would use, but as a starting point, I think it's PathMeasure that you have to use in order to inspect and analyse the data within the Path to begin with. Or, you might want to render them to bitmap and use some kind of image recognition library to compare those bitmaps, perhaps?

Answer 2

You can't really make a string for that object I think, so you get the default value: If you check out the manual you see that it is actually the same as

getClass().getName() + '@' + Integer.toHexString(hashCode())

or, in their words,

The unsigned hexadecimal representation of the hash code of the object.

It's just a hashed value of the object, and has no direct recognisable connection to for instance any features of the Path (location etc). If you really want to know how it is made you can find the hashCode() function of that object, but I suspect you won't see anything interesting for this question.

To be clear, when you say you want to compare "path values" you seem to imply that you want to compare above printed values. I don't see how you would want to need that. You probably want to check if 2 separately drawn/created lines are the same. You cannot use this hash for that purpose, you need to use the actual values like start/stop/angle/or something like that. (I'm not sure what members are present in a path, but you can look that up)