I'm coding iOS app that will explain complex numbers to the user. Complex numbers can be displayed in Cartesian coordinates and that's what I want to do; print one or more vectors on the screen.
I am looking for the easiest way to print 3 vectors into a coordinate system that will adjust itself to the vector-size (if x-coord is > y-coord adjust both axis to x-coord and vice versa).
I tried using Core Plot, which I think is way too multifunctional for my purpose.
Right now I am working with PowerPlot and my coordinate system looks okay already, but I still encounter some problems (x- and y-axis are set to the x and y values which results in a 45 degree angled line, no matter the user input).
The functionality of the examples in CorePlot and PowerPlot don't seem to meet my needs.
My last two approaches were using HTML and a web view, and doing it all myself with Quartz (not the simple way...)
Do you have any advice how to do this the simple way, as it is a simple problem, I guess?
If you're not wanting to do much actual graphing and plotting, then using Core Plot or similar sounds like overkill to me. The extra bloat of adding coreplot to your project, not to mention the time taken for you to understand how to use it, might not be worth it for some simple graphics.
Quartz is well equipped for the job of showing a few vectors on the screen, assuming you're not interested in fancy 3D graphics. There are plenty of tutorials and examples of using Core Graphics (AKA Quartz) to draw lines etc. If you're going the Quartz route, perhaps get some simple line drawing going in Quartz, then ask more questions if you need help with the maths aspect of it.
The typical technique used when rendering with Quartz is to override drawRect in a subclass of UIView and place calls to Core Graphics drawing functions in there.
A decent question and example of Quartz line drawing is here:
How do I draw a line on the iPhone?
If you aren't adverse to using Google Chart Image you can load reasonably complex data sets in a simple manner by calling the appropriate URL and then putting the image in a UIImageView. It takes very little code: here is a blog post explanation with sample code.
The limitations are
length of the data set is restricted by the max URL length you can request from Google (2048 characters, with encoding is large), though I've plotted with 120 data points in 4 series.
a net connection is required (at least to get the initial chart)
and perhaps the biggest problem, API is deprecated and will be discontinued in 2015 at some point. You would then have to switch to the UIWebView/Javascript Google Chart API implementation...
Sample image:
Related
I am researching into the best way to detect test in a photo using open source libraries.
I think the standard way is as follows (note: steps 1 - 4 all use OpenCV):
1) detect outline of document
2) transform document so it's flat and cropped, using said outline
3) Make the background of document white, using a filter
4) Feed resulting image to Tesseract
Is this the optimum process, or is there a better way, or better tools?
Also, what happens for case if the photo doesn't have a document outline (It's possible that step 1 & 2 are redundant)?
Is there anyway to automatically detect document orientation (i.e. portrait / landscape)?
I think your process is fine. I've used a similar process for an Android project.
I think that the only way you can discover if a document is portrait/landscape is to reason with the length of the sides of the bounding box of your outline.
I don't think there's an automatic way to do this, maybe you can find the most external contour approximable with a 4 segment polyline (all doable in opencv). In order to get this you'll have to work with contour hierarchy and contous approximation (see cv2.approxPolyDP).
This is how I would go for automatic outline detection. As I said, the rest of your algorithm seems just fine to me.
PS. I'll leave my Android project GitHub link. I don't know if it can be useful to you, but here I specify the outline by dragging some handles, then transform the image and feed it to Tesseract, using Java and OpenCV. Yeah It's a very bad idea to do that in the main thread of an Android app and yeah, the app is not finished. I just wanted to experiment with OCR, so I didn't care much of performance and usability, since this was not intended to use, but just for studying.
Look up the uniform width transform.
What this does is detect edges which have more or less the same width with respect to their opposite edge. So things like drainpipes (which can be eliminated at a later pass) but also the majority of text. Whilst conceptually it's similar to a distance transform, the published method uses rather ad hoc normal projection methods and Canny edge detection.
I have a lot of data to plot in a single plot window and it looks really ugly and not understandable. Moreover legends are coming on to the curves which make curves unreadable. I cannot put curve alone one by one into my latex report which makes it again difficult to maneuver between the plots.
My question is- can't it be possible to put all the curves in single plot generated from gnu plot which can be easily maneuver back and forth in a single plot window the latex report?
I know a bit about tikz pictures where no of frameworks can be easily accessible in single plot.
can't it be used for a whole curves one by one assuming as different frame work. and at last all the plots in the the plot window.
It would be very helpful if is possible so.
I have data with N rows and M columns in it. I need plots of N rows vs. each column separately to be shown in each frame in Latex generated report and in the last frame all the curves should be present. I need a proper procedure to follow to animate the curves.
Yes, this kind of thing can be done with the animate package in latex. I have successfully used it in the past for presentations that I put together with beamer. You could switch between different gnuplot graphs that are loaded into the animateinline environment, but you can also use pgfplots within tikz to modify the plot directly on your latex document without need for an external plot.
Using animate requires investing a bit of time at the beginning but the results can be very nice. Also, Okular (and I'm guessing other PDF viewers as well) seem to have trouble visualizing the animations but Adobe reader (acroread on linux) loads them without problems.
As an example, you can check a 5-minute presentation I put together last year: in slides 4 and 5 you can use the buttons to run the animation. The one in slide 4 includes plotting a gaussian with pgfplots changing the curve parameters between frames. You need to open it with the Adobe reader for it to play correctly.
New user to the site, but I have used it in the past so I felt it best to ask my question here, for the best chance of getting a response.
What I'm dealing with is one object, this being the sprite for my latest app, which I need to check for when it comes in to contact with another object, in this case, a tunnel which will curve.
Now, I'm aware of CGRectIntersectsRect, however I can't see that being helpful, as if I've got 2 UIImages, that being the top and bottom of a "mountain", and said pieces curving, there's no doubt that the sprite would touch the "rectangle".
What I need is something to trigger when the sprite hits the actual wall, however my limited knowledge of Objective-C isn't helping my case.
I imagine someone out there will know what I can do to resolve this, as for all I know it could be a simple solution.
Thank you in advance everyone!
First, I'd probably not build these basic pieces yourself. For iOS 7, you can use SpriteKit, which is built-in. If you want to support older versions of iOS, look at cocos2d (it's good for iOS 7, too).
But to the question, one approach for detecting arbitrary overlaps is to draw both objects into a buffer and check if there are any overlapping pixels (for instance, by drawing one in in pure red, and another in pure green, and then looking for pixels that have both). For a discussion of how to do this kind of thing in Core Graphics, see Clipping a CGRect to a CGPath, which provides sample code for the simplest version (checking for the intersection of a rectangle and curve), but the same approach can be used more generally. Note that this drawing can get expensive if you're doing it constantly, so usually you first check whether the bounding rectangles overlap. That tells you whether it's even worth the trouble to look closer.
But first I'd look at SpriteKit.
In my App I need to draw graph data with different datamodels that frequently change and can not be generalized. This graph data must be editable with a slider or a segmented control.
The idea is to load all necessary data to draw the graph from the server. Is html5 the right solution? Can the iPad-UI-Controlls used to manipulate the graph?
Where do I start and how much work is it?
Currently I'm using Core Plot to draw the graph - but I need to model my graph data on the server.
Option 1: If you are developing for Android as well or you are better at javascript, then you can use HTML5.0. Have a look at http://www.sencha.com/products/touch/charts/
Option 2: If you want to develop it natively for iPad(which I feel is a better option), then please look at google library for graph http://code.google.com/p/core-plot/ and Is there a good charting library for iPhone?
I extended the work of this gentleman:
http://buildmobile.com/creating-a-graph-with-quartz-2d/#fbid=EKAB22zV7It
And I'm quite pleased with the results. It took me about a week to get my graph able to draw a stock chart with scrolling, pinching zooming, 3 different symbol indicators, a secondary plot line, tap-able data points with a little custom popover showing details, and a few annotations. Not bad considering the overall complexity, and largely thanks to the detailed walkthrough.
He also talks about why he didn't use Core Plot.
Good luck,
Damien
I've never done OpenGL, but I'm looking for some pointers on this particular question on an AR app I'm practicing with.
I'd like to make an app with a "flat rectangle" along with text written on the surface of the rectangle. Visually, I'm imagining something along the lines of a piece of paper with text written on it. Each time the app starts, the text would be something different (the text is pulled from a plist file).
The user would be able to view the paper from all sides, much as if there was a piece of paper hanging in front of him.
Is this trivial to do in OpenGL? How could I get started?
Sorry for the really open-ended question, but I wanted to get a feel for how this kind of thing is done.
Looking at the OpenGL template source code in the Xcode sample projects, I see that there is a big array of vertices. I presume that to create a "flat" rectangle, I'd essentally just have to remove or make the z-axis zero. And then the dynamic text that will attach to the surface of the flat rectangle...I dont have any idea how to do that......
This question is hard to answer unambiguously. In general, this is trivial, but then again it is not.
Drawing a "flat rectangle with something on it" is a couple of API calls, as simple as it can get. Drawing text in OpenGL in an efficient way, and high quality, and without big preprocessing is an entirely different story.
What I would do is render text using whatever the "normal system-supported" way is under iOS (just like you would draw in any window, I wouldn't know this specific detail), but draw into a bitmap rather than on the screen. This should be supported, pretty much every OS has supported this for at least 10-15 years. Then turn this bitmap into a texture, bind it, and draw your trivial flat quad with OpenGL (set up a vertex buffer with 4 vertices, each vertex a texture coordinate, and draw two triangles - as easy as it gets).
The huge advantage of that is that you get to use the installed system fonts (or any fonts available), you don't need to generate a bitmap font and don't need to think about really ugly things such as hinting and proper spacing, and it's much easier to mix different text styles, etc. OpenGL has built-in support for text too, of course, but it is not terribly efficient or nice either. If the text does not change every millisecond, it's really best to render it using the standard renderer that the operating system provides (yes, that probably won't be hardware accelerated, but so what... since the user must read the text, it likely won't change every millisecond).
Now it gets more complicated if your "piece of paper" should bend and twist too, or do a page peel effect rather than being just a flat rectangle. In that case you need to tesselate it, which can be harder than it sounds, too. Not all tesselations look optimal for all bends/twists, or they do but do not have the optimal (read as minimum) number of vertices.
There is an article on "page peel" and such tesselation in one of the GPU Gems or GPU Pro books, let me search...
There: Andreas Bizzotto: "A Shader-Based eBook Reader - Page peeling effect", GPU Pro2 pp. 278-299
Maybe you can get hold of a copy or are lucky enough to find it on Google Books or something.