Define a minimum distance, say 10 dips.
Make or use a Vector2D class. (just x and y)
Allocate an array for your Vector2Ds.
pseudocode:
onPointerMoved() {
if (points.size() == 0) {
points.add(new Vector2d(pointerx, pointery));
} else {
Vector2D lastpoint = points.get(points.size() - 1);
if (distancefrom(lastpoint, pointerx, pointery) >
minimum_distance) {
points.add(new Vector2d(pointerx, pointery));
}
}
// analyze points here if you want to do it while user still moving
}
This will plot points as the user moves around, given a precision of
the minimum size you define. You can analyze the points while the
pointer is moving or you can wait until they let the pointer up and
then analyze. Checking for a direction of a vector is easy, it's
atan2((point0.x - point1.x) / (point0.y - point1.y)) but making more
sense of the graph becomes a bit more mathy.
Curve or arc recognition could be done in hackerish form by analyzing
4 or 5 points at a time (depending on precision, of course) and
calculating the average direction, min and max direction and minmax
direction delta then using those to decide what kind of arc it is and
mostly in what direction it was going.
So this is the "how," but without knowing more about exactly what
you're trying to do, this is all I can offer.
On Dec 30, 8:53 am, Paul <[email protected]> wrote:
> On Dec 30, 5:09 am, Daniel Drozdzewski <[email protected]>
> wrote:
>
>
>
>
>
>
>
>
>
> > > On Dec 29, 1:18 am, Paul <[email protected]> wrote:
> > >> Hi all. I am writing an app that will convert touchscreen user inputs
> > >> (such as the user 'handwriting' on the screen) into vectors that can
> > >> then be saved and recalled later. I need to get the vectors into a
> > >> format I can store locally, either as a file or in an SQLite
> > >> database. Just wondering if anyone had any pointers as to how to get
> > >> started... my initial thought was to listen for MotionEvents and when
> > >> an ACTION_DOWN is detected, record the coordinates and use this as the
> > >> vector's start point, and then record intermediate coordinates as the
> > >> ACTION_MOVE is triggered (used to help define the shape of this Path
> > >> they are creating), ending the stroke vector on ACTION_UP... but this
> > >> results in many many intermediate points per vector (30 or 40) and
> > >> with several hundred vectors (a full page of handwritten text on a
> > >> tablet for example) this solution gets quickly out of hand as each
> > >> page will potentially require tens of thousands of points...
>
> > >> Any suggestions on a better way to represent and store user-inputed
> > >> vectors/paths? Or maybe another approach completely?
>
> > >> Thanks for any help!
>
> > >> Paul
>
> > Paul,
>
> > You could blindingly start filtering any intermediate vectors, but you
> > would miss some important points, where the writing drastically
> > changes its direction.
> > As you see, the problem you have is detecting where the continuous
> > line changes its direction by much and intermediate points could be
> > filtered.
>
> > You would need calculating the angles between adjacent vectors and
> > when the angle gets bigger than some threshold value, the point
> > between said vectors becomes very important.
>
> > Hope this helps you somehow.
>
> > --
> > Daniel Drozdzewski
>
> I was thinking about this issue too... how do I recognize when a path
> backs onto itself, makes sharp turns, etc as is normal in
> handwriting? As I mentioned in another reply, I have looked at the
> SVG Path standard:
>
> http://www.w3schools.com/svg/svg_path.asp
>
> Looks like a possibility in terms of efficiently storing the shape of
> the stroke, but to use it I need to somehow take a set of coordinate
> points that Android spits out from MotionEvent and 'recognize' when it
> is a curve, arc, etc... maybe I extend my StrokeGestureDetector I
> mentioned to handle the heavy lifting of this recognitions, so that it
> simply reports back when the stroke is curved, etc? The issue remains
> how I determine when a set of x,y coords forms a curve, a sharp curve
> (such as when printing an M for example), etc. Off the top of my
> head, maybe in my gesture detector, when in a stroke, store the last 3
> MotionEvent points, generate a 'line' from point 1 to 2, and point 2
> to 3 and determine the angle at this vertex to help recognize
> direction changes? Again, the HOW is where I am stuck at this
> point... once I have the points described, recreating looks straight-
> forward simple using the built-in Path class.
>
> Any ideas on how to programatically test for the direction changes,
> curves, etc?
>
> Paul
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