I need to track single object's motion from frame to frame. I only need to know its position. But sometimes the object may go beyond the frame's boundaries partly (even most part) and sometimes it can approach the camera so closely that it will not fit in the frame. Which algorithm is the best for this purpose?
The question seems not to be specific. What are you tracking?
Is it just a colored object (which is simplest), use threshold method for that color and use contour or method of moment to find its position. Then even if it goes out and come back, still it will be tracked.
http://aishack.in/tutorials/tracking-colored-objects-in-opencv/
Or whatever it is, try to isolate the blob first.
And if i misunderstood the question, please specify with few more details.
Related
I need to be able to interact with a representation of a cilinder that has many different parts in it. When the users taps over on of the small rectangles, I need to display a popover related to the specific piece (form).
The next image demonstrates a realistic 3d approach. But, I repeat, I need to solve the problem, the 3d is NOT required (would be really cool though). A representation that complies the functional needs will suffice.
The info about the parts to make the drawing comes from an API (size, position, etc)
I dont need it to be realistic really. The simplest aproximation would be to show a cilinder in a 2d representation, like a rectangle made out of interactable small rectangles.
So, as I mentioned, I think there are (as I see it) two opposite approaches: Realistic or Simplified
Is there a way to achieve a nice solution in the middle? What libraries, components, frameworks that I should look into?
My research has led me to SceneKit, but I still dont know if I will be able to interact with it. Interaction is a very important part as I need to display a popover when the user taps on any small rectangle over the cylinder.
Thanks
You don't need any special frameworks to achieve an interaction like this. This effect can be achieved with standard UIKit and UIView and a little trigonometry. You can actually draw exactly your example image using 2D math and drawing. My answer is not an exact formula but involves thinking about how the shapes are defined and break the problem down into manageable steps.
A cylinder can be defined by two offset circles representing the end pieces, connected at their radii. I will use an orthographic projection meaning the cylinder doesn't appear smaller as the depth extends into the background (but you could adapt to perspective if needed). You could draw this with CoreGraphics in a UIView drawRect.
A square slice represents an angle piece of the circle, offset by an amount smaller than the length of the cylinder, but in the same direction, as in the following diagram (sorry for imprecise drawing).
This square slice you are interested in is the area outlined in solid red, outside the radius of the first circle, and inside the radius of the imaginary second circle (which is just offset from the first circle by whatever length you want the slice).
To draw this area you simply need to draw a path of the outline of each arc and connect the endpoints.
To check if a touch is inside one of these square slices:
Check if the touch point is between angle a from the origin at a.
Check if the touch point is outside the radius of the inside circle.
Check if the touch point is inside the radius of the outside circle. (Note what this means if the circles are more than a radius apart.)
To find a point to display the popover you could average the end points on the slice or find the middle angle between the two edges and offset by half the distance.
Theoretically, doing this in Scene Kit with either SpriteKit or UIKit Popovers is ideal.
However Scene Kit (and Sprite Kit) seem to be in a state of flux wherein nobody from Apple is communicating with users about the raft of issues folks are currently having with both. From relatively stable and performant Sprite Kit in iOS 8.4 to a lot of lost performance in iOS 9 seems common. Scene Kit simply doesn't seem finished, and the documentation and community are both nearly non-existent as a result.
That being said... the theory is this:
Material IDs are what's used in traditional 3D apps to define areas of an object that have different materials. Somehow these Material IDs are called "elements" in SceneKit. I haven't been able to find much more about this.
It should be possible to detect the "element" that's underneath a touch on an object, and respond accordingly. You should even be able to change the state/nature of the material on that element to indicate it's the currently selected.
When wanting a smooth, well rounded cylinder as per your example, start with a cylinder that's made of only enough segments to describe/define the material IDs you need for your "rectangular" sections to be touched.
Later you can add a smoothing operation to the cylinder to make it round, and all the extra smoothing geometry in each quadrant of unique material ID should be responsive, regardless of how you add this extra detail to smooth the presentation of the cylinder.
Idea for the "Simplified" version:
if this representation is okey, you can use a UICollectionView.
Each cell can have a defined size thanks to
collectionView:layout:sizeForItemAtIndexPath:
Then each cell of the collection could be a small rectangle representing a
touchable part of the cylinder.
and using
collectionView:(UICollectionView *)collectionView
didSelectItemAtIndexPath:(NSIndexPath *)indexPath
To get the touch.
This will help you to display the popover at the right place:
CGRect rect = [collectionView layoutAttributesForItemAtIndexPath:indexPath].frame;
Finally, you can choose the appropriate popover (if the app has to work on iPhone) here:
https://www.cocoacontrols.com/search?q=popover
Not perfect, but i think this is efficient!
Yes, SceneKit.
When user perform a touch event, that mean you knew the 2D coordinate on screen, so your only decision is to popover a view or not, even a 3D model is not exist.
First, we can logically split the requirement into two pieces, determine the touching segment, showing right "color" in each segment.
I think the use of 3D model is to determine which piece of data to show in your case if I don't get you wrong. In that case, the SCNView's hit test method will do most of work for you. What you should do is to perform a hit test, take out the hit node and the hit's local 3D coordinate of this node, you can then calculate which segment is hit by this touch and do the decision.
Now how to draw the surface of the cylinder would be the only left question, right? There are various ways to do, for example simply paint each image you need and programmatically and attach it to the cylinder's material or have your image files on disk and use as material for the cylinder ...
I think the problem would be basically solved.
I am working on a small education demo which should measure height and width of the object using iOS camera.
EDIT:
I have a new theory to measure the width of an object.
In above image, if i can get Angle α and Angle ß, i can get width of the unknown side by using trigonometry formulas. I have the values of b1 and b2 already.
OLD:
Right now, i am focusing on measuring length only.
As per my knowledge it should be 3 step process.
User snaps one end of the object.
User snaps other end of the object.
User snaps center of the object. (Suggest me a better way for these please)
I get the approximate measurements using above process, but for the 3rd step, in which user snaps the center of the object. I want to show pointer location on screen (as camera overlay) to help user determine the center of the object.
This is how i am doing it right now.
How can i draw pointer location for 3rd step?
Note: Please suggest alternative/best way to make it possible. I would love another suggestions. Thanks.!!
First of all I must appreciate your work you have done till now. Another good thing is the way of explaining, salute!!!!!
After reading of your question, I feel that you dont need code, you can do it. I think you need direction only.
As per your explanation, you want to record angle of rotation of the device.
If you want to measure angle of rotation, you have to use compas readings. But compas readings will change if user tild the device. So you have to use accelerometer to measure tilding of device.
In short you have to make some combination and equation of both compas and accelerometer readings. Use compas to measure angle and use accelerometer to measure tilding of device.
If you want further information to implement it, you can ask me.
Hope this will help you....
I have been struggling with this problem for a time and being unable to solve it led me here. I'm recently new to Actionscript (2.0). I want to do something similar to:
http://gnarshmallow.com/
Were i want something to be painted behind a moving object in real time.
I would like some advice on how to approach the problem.
You need to use line drawing to do this. You will need two points, and it will draw a line from one to the next. I recommend having it run on every movement call. Have it draw the line between the racer's location in the previous frame, and his location in the current frame. For further reference, check out this page.
http://www.actionscript.org/resources/articles/730/1/Drawing-lines-with-AS2/Page1.html
In the Video Session 506 of Apples WWDC 2012 they showed a painting app which is made for high performance drawings (so the frame rate never gets below 30).
I tried to replicate the code but get stuck on multiple points.
What I am looking for is a basic drawing app (lines, Squares, Circles, bezier paths), which performs well even after hundreds of lines have been drawn.
The basic approach is to save the drawn lines (or circles bezierpaths etc) to an image after a certain numbers of them have been drawn, and then only refresh the new drawings, therefore not having to redraw all the already drawn lines.
But somehow I never get to a higher performance. How do I need to implement this? Do I need multiple layers? And how do I manage that not all layers in a view are redrawn, but only a certain sublayer?
If someone could provide me with a short example of a few lines drawn on an layer, then saving that layer to an image, an then drawing on top of that I would really appreciate it.
Thank you for any help to recreate the iPaint application, which is unfortunately not available for download from apple.
That is only half of the puzzle. The other half is to only refresh the minimum possible area of the view (via setNeedsDisplayInRect:). However, I have been through many different ways of drawing via Core Graphics. The caching is fine, but I don't use it anymore. I set the update rectangle as above, and then test each path before I stroke it (testing is fast, stroking is slow). If it is inside the update box, I stroke it, otherwise I ignore it.
I did not look at that session, but a traditional Quartz speedup has been to use CGLayers (not CALayers). You can think of a CGLayer as a cached drawing which may or may not be a bitmap (the system decides how best to cached it). If you have a backing bitmap context, you can use that as your "image" and draw the CGLayers into that (and then discard the layers) as you see fit. Read up on CGLayer (its in the Quartz documentation) and then see if this was what they talked about in that session.
I'm subclassing CALayer to provide my own drawing in method. For optimization I call -[MyLayer setNeedsDisplayInRect:] instead of -[MyLayer setNeedsDisplay]. In the drawing method I get the rect which should be redrawn via CGContextGetClipBoundingBox().
If I use this layer as the base layer of an UIView every thing works as expected. The problem arises, as soon as I use my custom layer as a sublayer of an other CALayer. Than CGContextGetClipBoundingBox() always returns the rect of the bounds of that layer.
Any ideas?
[EDIT]
It seems, that there is no guaranty, that the content of the CALayer is cached and only the dirty part gets redrawn. I did a small test and stored the rect that needs display as a separate property. The result was, that only this part was visible on the screen.
I'll now render to an image context and keep that image as a cache. In the draw method I'll only display the cached image.
Apple's documentation is unfortunately conflicting as the docs on -setNeedsDisplayInRect do not indicate whether the method works in practice. Based on my own experience, this technote sets it straight:
Note that, because of the way that iPhone/iPod touch/iPad updates its screen, the entire view will be redrawn if you call -setNeedsDisplayInRect: or -setNeedsDisplay:.
That being said, there are a number of things you can look into if you think that you are hitting a wall due to redundant drawing.
If drawing images, the biggest performance improvement you can make is to use images of the same dimensions at which you draw. If they're not, try to cache your image by rendering it to some offscreen bitmap context and bring it back later on.
Check out the shouldRasterize property on CALayer. This can be a godsend if you are trying to manipulate a layer whose sublayers potentially constitute a complex layer hierarchy. Be sure to check out how you're doing in Instruments by ticking the Color Hits Green and Misses Red box in the Core Animation instrument. If you see a lot of red, chances are using shouldRasterize is hurting more than it's helping.
Even better than shouldRasterize is to flatten your layer hierarchy, as then you can avoid the extra overhead that shouldRasterize incurs when flattening your layer hierarchy real time. Of course this is not always possible, but don't be afraid to try :)
If you're drawing images, try experimenting with your blending mode. If you happen to be drawing opaque images, there's no need to be using normal source over methods (which use both read/write bandwidth). Try kCGBlendModeCopy, which allows you to eliminate read bandwidth overhead.
Check out CGLayerRef, which allows you to cache Core Graphics output across various calls to your drawing methods. My experience is that, unless you're doing some hardcore pixel pushing, that this ends up being more costly than just redrawing. See this for an interesting read.
Above all, Instruments is your friend. Check out a couple videos from past WWDCs (2012, 2011, and 2010); they all have great info about how to fine-tune performance.
Please feel free to ask any further questions if something I've said makes little sense.