I'm trying to use Leaflet.js to access a non-geo (scanned image ...) map, which I tiled using gdal2tiles.py -p raster. But I absolutely can't get it to work: I see Leaflet requesting URLs with negative coordinates and non-existent ones. (Such as: /3/-1/8.png ...)
The map in question is 1162 pixels wide and 700 pixels high.
The tilemapresource.xml file generated by gdal2tiles says, among other things:
<BoundingBox minx="0.0" miny="-700.0" maxx="1162.0" maxy="0.0"/>
<Origin x="0.0" y="-700.0"/>
So, as you can see, the Y coordinates range from a negative number to zero, and the X range from zero to a positive number. (That's just the way that gdal2tiles.py decided to do it, I guess.)
I am using CRS.Simple like all the documents say to do, and I'm setting the bounds to SouthWest=(-700,0), NorthEast=(0,1162), admitting to be already mightily-confused when I see other examples that seem to be reversing the second (Lng) coordinate.
(I realized that "Lat" corresponds to "Y" and "Lng" to "X.")
Equally puzzling to me is that when I unproject the Southwest and Northeast points using the max-zoom, I get LatLng(-36.3125, -21.875) for SouthWest. I don't know why. (Again, I am using CRS.Simple ...)
Experimentally, I set "tms: false" on the tile-layer, which caused something to show up, but now the display's doing the most amazing thing: entirely on its own, it's "ping-ponging" back and forth along a line from roughly the middle of the right-hand margin down-and-left to the middle of the bottom, and back.
I know I've been whacking at this thing for too long today...
Well, I found it. (And, since I wound up asking this question twice, let me answer it in both places.)
Add all of the layers that you are going to use on your map, when you call the Map object's constructor, using the layers option.
In other words, do not do as I was doing: try to set up the various layers first, then add them to the map. The map needs to know about the layers, and the layers need to know about the map, right from the start. So, add them, then configure them as you need.
Otherwise, "strange and default things may happen." For example, although I specified the Simple CRS, that's not what I effectively wound-up with. It appears that the various objects (map, layers), "talk to one another" quite a bit with this library, and they don't expect to be orphans.
(Some of the "strange things" that can happen are, in fact, bizarre ... like: a tiny version of the map, ping-ponging between "about three o'clock" and "about six o'clock" and back again. A funny and entertaining thing to look at, unless you don't yet know why it's happening, nor how to stop it! Whew! )
The design of "leaflet.js" certainly isn't wrong, to be sure, but it has some unpleasant surprises for the unwary. (Like me.) Hope this helps.
Related
I'm working on MATLAB on some regions inside an image. I'm at a point in which I would like to be able to separate regions which exhibit some kind of regularity (e.g., being circle-ish or square-ish) from regions which does not resemble any known figure and which for my application are mere noise. I'll illustrate this using a descriptive MS Paint image:
Is there any tool that, most of the times (or even less, I know this can't be 100/100) will recognize the red thing as being different?
I'll deal with many shapes in a single image, so I don't mind if I carry on some red monsters along the way, as long as the majority of them is kicked out. Of course I know the indices of these regions, so I can manipulate them in MATLAB.
Many algorithms come to mind, e.g., getting the boundary and checking for its regularity/the number of times it changes curvature/..., checking for variations in vertical length through different columns (nearly 0 for the linear feature, really high for the red stuff), ...
However I was hoping in some help from a tool out there. It doesn't matter if this tool won't cover all cases (for example, will kick out circles), I've been very broad to get the maximum number of inputs from you guys - any tool will be inspiring and helpful (and, however, we can't expect a perfect answer for the deeper question - recognizing regular shapes - which seems more like a AI field of research). I also think that, while being broad, this is totally non-subjective so should fit in SO. Thank you.
Side note 1: I'll deal mostly with elongated, extended features like the top-right one, so circles are not that relevant.
Side note 2: To be 100% clear, I would need something (be it an already existant tool, or some ideas pointed out by you) that acts on the indices of the shapes, in terms of rows-columns into the original image, or on the boundary of the shape itself.
Side note 3: Apart from tools/suggestions/ideas, you are welcomed to write down some lines of code ;) I'm getting the regions as connected components from bwconncomp.
I had to solve a similar problem recently that involved counting the number of indentations on blobs within in an image (basically, the connected components returned by bwconncomp). The method I used was to look at curvature changes along the boundary calculated via the FFT. In your case, the red blobs would have a large number of curvature variations, whereas the black regions would not. It's a pretty easy calculation and relatively fast. The code is on github here:
https://github.com/mjsottile/blobdents
The file of interest is src/countindents.m. A short description of the approach is here:
http://arxiv.org/abs/1501.07692
I went for the easier road as suggested by #Mikhail in comments.
I found out regionprops has a really helpful tool called Solidity. Quoting docs,
Returns a scalar specifying the proportion of the pixels in the convex hull that are also in the region. Computed as Area/ConvexArea.
Convex hull is defined as the smallest convex polygon that can contain the region. So Solidity goes up to 1 if the shape is kind of regular and has no convexity changes; down to 0 for my red shape, which leaves space between itself and the convex polygon.
Of course it never reaches 0, lowest value should belong to a kind of +-shaped sign.
Given a set of non-rotated AABB bounds, I'm hoping to create a simpler set of bounds from the original set, that allows for a specified amount of inaccuracy.
Some examples:
I'm working with this in Unity with Bounds, but it's just basic AABB comparison stuff, nothing Unity-specific. I figure someone must have worked out a system for this at some point in the past, but I had no luck searching around. Encapsulating bounds are easy but this is harder, since you can't just iterate through each bounds one by one. Sometimes a simpler solution can only be seen by looking at the whole thing.
Fast performance isn't critical but would be nice. Inaccuracy is OK in both directions (i.e. the bounds may cover a little less than the actual size or a little more). If it helps, I can expect all bounds in the original set to be connected somewhere - no free-floating pieces in a separate group.
I don't expect anyone to write up a whole system to solve this, I'm more hoping that it's already been solved or that maybe there's an obvious process to achieve it that I haven't thought of yet.
This sounds something that could be handled with Surface Area Heuristics (SAH). SAH is commonly used in ray tracing to build better tree like structures were the triangles are stored. There are multiple sources discussing it more. One good is Wald's thesis chapter 7.3.
The basic idea in the SAH built is to start with the whole space and divide it recursively. Division position is decided by sweeping through all reasonable positions and calculating surface area of both child nodes. The reasonable positions are the positions were any triangle has its upper or lower bound. After sweeping through all the candidates, the division with the smallest total surface area in the children is used.
If SAH is not a good idea for your application, you could use similar sweeping through all candidates, but calculate for example the extra space inside the AABBs.
I would like to track (if that is the right word for this) the movement of a point on an object and return the co-ordinates for the point in each frame to arrays for plotting. How would you go about doing this?
The point on the video is a certain color and so my first effort was to eliminate all other colors and change the part I wish to follow to black and everything else to white. Doing this left me with some areas in the background which are the same color but I wish to ignore them and just focus on the moving point. I do not know where to even begin with this or if I've even been trying to do the right thing so far?
Any help would be greatly appreciated! :)
Try searching for terms like 'tracking', 'morphological', 'computer vision', 'matlab'
Here's a project that I found that will probably get you started.
http://www.mathworks.com/matlabcentral/fileexchange/28757-tracking-red-color-objects-using-matlab
if your object of interests is of a certain specific color. You can always apply a color-filter. To give you a bit of a background, i was trying to track not a point on an object, but a moving object in one of the videos i have. (it was a ping-pong video and my goal was to track the ping-pong ball). My algorithm was simple and fast (as i did not want any of my filters to induce heavy computations at one single frame). The basic idea was to apply a color filter. Similar to other shape filters, if your target is of high similarity to the filter, the response will be distinctive enough for you to notice. In other words, if you minus two objects that are extremely similar, you will get 0, otherwise, it will be far greater than 0.
I need to create an algorithm to layout some hierarchical data but have never done this kind of thing before and need some broad tips.
Basically I need to recreate this diagram (with dynamic data):
diagram http://dl.dropbox.com/u/15126868/diagram.png
bigger
I don't have a problem with most of it but need help with two things:
How do I approach writing a layout algorithm?
Should I use UIView subclasses for all discs or use quartz (I do need interaction)
Any suggestions most welcome. I don't need too much detail.
A bit more detail:
I'm currently thinking I should use UIView subclasses and layoutSubviews. Trouble is I need to know the size (at least roughly) of all nodes before I can start to position them. Then, as the positioning involves rotation, I may need to adjust child positioning again - and I can't add labels until after any rotation.
Other considerations seem to be: that the presentation area is rectangular, not square; that I can't spill off the page; and that I will need to animate changes to the sizes of the discs.
Any pointers would be great, thanks.
This sort of thing is very difficult.
Interestingly the perhaps main actual initial constraint here is the size of the typography.
In the example given: Observe they could have chosen a different SCPT** somewhat larger (perhaps, 10%-15% larger) or somewhat smaller and it would have still worked. They made an aesthetic decision on the SCPT.
White space is critical to design. Their particular graphic designer happened to like the particular feel of white space which you see. But it would have by no means been "wrong" with a smaller SCTP. Further, observe they could have used an even larger SCPT ... IF ... they used a smaller point size on the typography.
Note that in any event you simply won't be able to display that much type that small on an iPad (or Fone4).
So straight away you have to make decisions about how the type will appear, popup, audio or whatever. Even the white type ("on the discs" type) will give you trouble.
You will have to do lots of tests with photoshop first on to your iPad before even proceeding with an algorithm. So purely for what it's worth...
Here's how I personally would do this sort of thing. In general plan: I would try to do a squishy algorithm that retries itself until it finds a result it is happy with.
IMHO, based on previously doing this type of thing: this problem is too hard to get it done in one go with some particularly smart-ass heuristic. Since there is no one smart-ass heuristic that will save the day, I'd do this:
1) calculate the total trillions to display. (it looks like about 2.5 is the total in the example image)
2) guess a SCPT value to begin with. what about for example "18" based on the actual image at the screen size we see above as posted inside your question.
3) put the big one (sun) in the dead center, and for the middle ones (planets) -- just choose a very easy heuristic, what about from biggest to smallest going anticlockwise srtaing at the top left (don't try to get clever than that with that part of the problem - which indeed could be a huge research project purely on it's own) .. and do the same with the small ones (moons).
4) for the sticks between planets and moons - adopt a trivial solution (like "always 0.5 cm"!!) and that's that. with AI you gotta cut your losses .. everywhere! :) Fix the moons to the planets and forget about them.
5) Now a hard part .. run some sort of heuristic over them that evenly balances what you have so far. treat color as mass and no color as no mass and move the "sun" until it is balancedish. (to be clear, as an example that would be likely downwards if you followed the "planet" layout mentioned in 3.) maybe also move all the planet/moon systems in-out to try to balance it.
6) next the iteration. look at that result and decide if you like it! go back to (2) and pick a new value. (maybe "16!" for example)
(7) there are two possible outcomes here. it might be that during development, there is one magic value for SCPT that always works. perhaps "14.3" or "18.2" or whatever. if you find such a value, never tell anyone. keep it as your own secret information!!!! milk it for everything it is worth with clients. conversely and more difficultly, you might find you need a different value each time. in that case: your AI will have to on it's own iterate through values until it finds one it likes. (for example, by determining whether all your labels fit or not .. and obvious things like "are they touching" "all on screen" etc.)
Anyway FWIW (perhaps nothing) that is what I would do - an iterative approach based on a first guess for the SCPT.
Incidentally: you may well want to buy and study the classic and brilliant book on this sort of display of information!!! Everyone should have a copy.
Tufte's The visual display of Quantatative Information
by Edward R. Tufte
ISBN 0961392142
Regarding the mechanics of laying out the image. You should use quartz or any other low-level drawing - forget about UIViews and the like. You should surely completely separate the logic from the drawing layer, so (even if you do want to change to UIViews, OpenGLES, or whatever) it's only changing a few lines of code.
Hope it helps somehow.
Notes...
** SCPT .. square centimeters per trillion
Followup...
"To keep the logic separate would you use a manager-type pattern?"
To be honest: if I was doing it, I would just start a whole new app purely for the "research" of getting this part, this challenge, working right. In that app (to be honest!) I would make bugger all effort to do anything in any tidy manner whatsoever! :-/ Globals everywhere! :) Unfortunately for me I can only think of the one thing at a time, so at that stage I would only be thinking about the algorithm, per se.
I believe, once you cracked the problem per se, once you came to implement it in a bigger project ... really, FWIW, if it was me, I'd simply make it a class (let's say AmazingClass) nothing more complicated than that. Personally I would set the data somewhere separately (whether in a DB or just an array or whatever) and I would just let the AmazingClass take care of getting the data, even. (My thinking - you never know how the hell you're going to need the data and when, at what point in the process of AmazingClass. So, just give up and let AmazingClass take it as and when it wants it.)
If you are familiar with these awesome-sounding manager-patterns of which you speak - yeah, why not! In short I would heavily separate it out as much as possible. I'm not good enough to speak on the best way to do that - but just completely separate it out somewhere. Sorry I can't help on that one.
I am trying to make an iPhone application which can draw a path between two points (similar to Google Maps) but instead of the map i want to use any other image as a background, this path between the two points might not be straight and there might be multiple paths to get from one point to another then I want to draw the shortest path between the two points.
I tried using the CGContext & CGPath but I got stacked.
Can you help me plz.
Thanx,
Ghaith
I think you're looking for UIBezierPath. You can add simple lines/polygons with something like:
UIBezierPath* path = [UIBezierPath bezierPath];
[aPath moveToPoint:CGPointMake(50.0, 50.0)];
[aPath addLineToPoint:CGPointMake(10.0, 10.0)];
[aPath addLineToPoint:CGPointMake(10.0, 50.0)];
[aPath closePath];
You can also, of course, add curves (bezier ones!) and other shapes. Then to draw it use the [aPath stroke] call in your view's drawRect method.
For more information see the iPad Programming Guide
This seems like a problem that's not really related to drawing the route.
You want to find the shortest path from one point to another, given certain criteria - where you can and cannot move, for example. I don't see this problem as something you can solve with drawing, but with actually calculating the different possible ways and then compare them. When you have decided which is the best route. Drawing is pretty simple.
How you would go by deciding I'm actually not sure - sorry 'bout that. But you should probably have a look at some shortest path algorithms. But that probably means you have to represent the underlying image as a pattern, or a series of nodes but graphical problems are not my cup of tea, so I'm not really sure how.
Just a side note - If the number of possible ways of getting from point A to point B are great, this can become a computational problem, and you have to make sure that the iPhone can manage.
(this should probably be a comment somewhere, but since I can't yet and I still wanted to share my two cents, it became an answer.)
Edit:
I just thought of really naive aproach! - for fun mostly, but I couldn't keep myself from posting.
Suppose you have a representation of the image. What parts can't be traveled on and what parts can be. Each pixel that can be travelled on is represented by a 1, and every other pixel is represented by a 0. Thus the pixels represented by 1s can be seen as nodes on which we can travel.
Each node can reach, at most, 8 other nodes - the adjacent pixels. And the weight of travelling between any two nodes could be set as 1. But we have to account that travelling in a diagonal is a greater distance so that weight should be sqrt(2).
Now we have a great bunch of nodes - each with weights in between them. From here we can apply a djikstra-algorithm to find the best route. (maybe some other algorithm is more beneficial at this point - but djikstras is the only one I'm familiar with).
hum, wonder how bad of a solution this would be. ... again, you probably don't want this solution...
EDIT 2:
I will say this again that this is probably not the best way to do this! You should seriously ask someone with more experience in algorithms and in graphical problems. - This was something I thought of at 3am and was mostly for laughs.
If your question is about calculating routes instead of drawing routes, that's a whole different problem. The standard algorithm for finding efficient routes through a given space are the "A*" (pronounced A-star) algorithms, which are typically what real-time strategy games use when you click a unit and tell it to "go there". It's also got many uses in AI when searching for a transition through a space.
It's not easy to get right, though. It might be easier to find a good game engine that already includes an A* implementation and integrate that into your software.