I have calculated field of view
float FOV = camera.activeFormat.videoFieldOfView;
But its the iPhone field of view.
I need to calculate width of object using field of view. How can i calculate either
1) Field of view for particular object
or
2)Width of object using Camera
i have below mark in the pic :
Angle AOB =FOV i have
A'O and B'O i have calculated already.
Need to calculate
angle A'OB' and using which finally my aim to calculate A'B' (width of object)
You need 3 independent informations about a triangle to characterize it, otherwise you are just describing a class of triangles. Informations can be angles or lengths.
In your case you have two information about triangle OA'B' and one about OAB, so you can't do anything.
If you had more information, as the horizontal % of the screen taken by your object, you could find a relation between FOV and the angle A'OB' you need by multiplication. (X% * FOV= A'OB')
Now if you have A'OB', OA' and OB' you can compute A'B' with trigonometry.
If I'm understanding you correctly, you still need the distance to the object. Once you have that, you have two sides of a triangle, and can now calculate A'OB', as follows:
Let's call A'B'/2 (i.e. the midpoint of A'B'), C'. (OC' is then the distance to the object.)
A'C'O (or B'OC') form a right triangle.
OC'/OA' is equal to the cosine of A'OC'.
If we multiply the arccosine of OC'/OA' by 2, we will end up with the angle A'OB'.
If you just want the length of A'B', things become even simpler. Multiply the square root of (OA' squared minus OC' squared)' by 2, and you'll have the length of A'B'
Does that make sense?
Related
In answer to another question, Sushanth stated:
The lowest point of the rectangle(does not matter left or right) will always be the first sub-list of the "box" ndarray. So in the example I have given, the first sub-list [169 144] represents the "bottom right of this rectangle".
Now this point will be the reference point to decide what the next sub-list represents. Meaning, the next sub-list will always represent the point that you first get when you move in the clockwise direction. (as shown in the second image of the for loop)
I don't understand how to tell if the lowest point is the bottom-left or bottom-right point on the bases of the "first sub-list".
I need to create a generalized code that can tell them apart so that I can reliably apply warpAffine transformation to a dataset of images (as shown here).
This is Sushanth's answer to my question:
To determine whether it is a bottom-left or right in a scenario when
the two bottom points have the same y-coordinate: i. First, have a
conditional statement to see whether the two bottom points have the
same y-coordinate. ii. If the condition is True, then check which
coordinate has the lowest x-value(or the highest). The coordinate
with the lowest x-value will be bottom-left of course! "How did you
determine this just by looking at the sub-list?" -- I did not
determine it by just looking at it! I could not! This is exactly why I
wrote the above for-loop in my answer!
with minor spelling corrections from my side
I learned later on that I actually didn't need that information for performing warpAffine transformation as the angle information is returned by minAreaRect
def warp_contour(img,cnt):
rows, cols = img.shape
rect = cv2.minAreaRect(cnt)
center,_,angle = rect
box = cv2.boxPoints(rect)
box = np.int0(box)
rot = cv2.getRotationMatrix2D(center, angle, 1)
img = cv2.warpAffine(img, rot, (rows,cols))
return img
But I won't be accepting this answer as I still want to know how to tell them apart.
SCENARIO
I am working on an application that keeps track of blood glucose levels into a graph. On the graph there are "markings" (ex: -200mg) going in vertical order along the y axis on the right side of the screen and "hours" (ex: -12:00 PM) will be along the x axis on the bottom of the graph. I have to plot out little 'dots' to display what the blood glucose level was throughout the way.
ISSUE
I am trying to calculate how to position the 'dots' in the correct time and mg level and I'm having difficulty calculating the positions. I can access the "markings" and retrieve it's marking.center.x to indicate which 'Time Slot' (x axis) and the marking.center.y to indicate which 'MG Level' the 'dot' needs to go into. Problem is it isn't always exactly 12:00 PM or 200mg where it will need to be placed. In fact that would be very rare.
WHAT I NEED
Based on the following variables:
dot.mgLevel
The dot will already know where it needs to go based on the information retrieved from the medical device. It will know the time and mgLevel to assign itself.
marking.mgLevel
The markings will each have evenly distributed values that such as -100mg, -200mg, -300mg ect...
timemarking.timeslot
Each time marking on the bottom will each have evenly distributed times allocated every 30 min. Such as -12:00PM, -12:30PM, -1:00PM ect...
If the dot has a mg Level of 330mg and the closest marking on the mg Level is 300mg, then I need to be able to calculate how much further up the dot needs to move from 300 going towards the 400mg marker.
SO...
If the distance between the markings are 100pt and the dot's mgLevel is 330mg, then I know that I need to move the dot from the 300mg marking toward the 400mg marking by exactly 30pt. That's because it's simple math because the distance between the markings is 100. But in real life it isn't 100, so I need to be able to calculate this.
MY ULTIMATE QUESTION
Say distance between markings is 241 and each marking represents multiples of a hundred. Say my dot has a mgLevel of 412. How do I calculate how far I need to move the dot so that it will be in the correct place?
I THINK?
I think I need to make 241 equal 100%. But I need help.
Distance between markings is 241pt
Markings are multiples of 100mg
1mg will occupy 2.41pt. So 412mg will occupy (2.41 * 412) pt. To know how much to move for the next dot, take the difference in mg and multiply by 2.41.
In general, if distance between 2 markings in points is d, markings are multiples of m, and desired accuracy is k decimal places, 1mg will occupy g:
let divisor = pow(10.0, Double(k))
let g = round((d/m)*divisor) / divisor
I'm following this tutorial
The goal is to be able to spit out either:
a. the center of each labeled object
b. all pixels associated with each labeled object
in a way that I have an array of either 'a.' for each object, or 'b.' for each object
I'm really not sure how to go about this. Are there matlabl tools to help extract these set of pixels or centers - per - label?
Update
I did manage to circle 80% of what I wanted using reigionprops, however it doesn't capture label precisely, just sets a circle around them while capturing the background as well, is that really unavoidable? I'm just not sure how to access the set of pixel per each circled item.
r=regionprops(L, 'All'); imshow(imagergb); areas={r.Area}; Bboxes={r.BoundingBox};
for k=2:numel(r)
if areas{k}>50 && areas{k} < 1100
rectangle('Position',Bboxes{k}, 'LineWidth',1, 'EdgeColor','b', 'Curvature', [1 1]);
end
end
So what I'm trying to do is for example.
I thought it might just be
r = regionprops(L, 'PixelIdxList')
then
element1 = r(1).PixelIdxList
but couldn't figure out how to get the position of each pixel
I also tried
Z= bwlabel(L);
but imshow(Z==1) spits out all labels and imshow(Z==2) spits out background, all labels and background. couldn't test bwlabeln since I'm not exactly sure what to enter for r and c arguments.
Using regionprops(L, 'PixelIdxList') is correct. It gives you lists of pixel indices for each label. You can then convert them to [x,y] coordinates using (for the first label, for example)
[y,x] = ind2sub(size(L), r(1).PixelIdxList)
You can get label centers by using regionprops(L, 'Centroid'). This already gives you [x,y] coordinates for each label. Note that these are subpixel coordinates, so you may need to round them if you want to use them as indices.
How to get Random Geo-points[ lat/long in decimal], placed anywhere inside a 100 meter radius circle? The center of the circle is another reference GeoPoint.
Is there any Function/Formulae that implements this?
Basically I am reading the GPS input of my android device and need to generate random Geo-Points around the device [In a circle of radius 100 meters centered at my device].
Please note : There are no Geo-Points pre-stored in Database. I need to create all the Geo-points on the fly as mentioned above.
I just wrote a a Ruby method which extends Random to provide this.
Caveat: The points all lay within a box, not a circle.
class Random
def location(lat, lng, max_dist_meters)
This is called with Random.new.location(mid_lat, mid_lng, dist). It will return a point which is probably within max_dist_meters of a the mid point.
max_radius = Math.sqrt((max_dist_meters ** 2) / 2.0)
Without adjusting to max_radius we'd get points inside a square outside the circle (i.e. in the corners), where the distance would be greater than max_dist_meters. This constrains us to a square inside the circle which is probably more what you want.
lat_offset = rand(10 ** (Math.log10(max_radius / 1.11)-5))
lng_offset = rand(10 ** (Math.log10(max_radius / 1.11)-5))
The 1.11 and 5 come from here.
lat += [1,-1].sample * lat_offset
lng += [1,-1].sample * lng_offset
lat = [[-90, lat].max, 90].min
lng = [[-180, lng].max, 180].min
We should probably wrap around here instead of just clamping the value, fixes welcome.
[lat, lng]
end
end
Comments / clean up welcome!
Sample output here which you can see nicely if you paste the lat/lngs here.
Pick random points on a square (i.e. pairs of uniform random numbers), then discard any that don't lie within a circle inscribed in that square. Given (x,y) pairs, a point is within your circle if:
(x - c_x)^2 + (y - c_y)^2 < r,
where (c_x, c_y) is the centre of your circle and r is its radius.
Start here: Generate a random point within a circle (uniformly). Then figure out how to center that circle at the reference lat/long. Then figure out how to map the randomly generated points to lat/long values. Hint: you want to add the individual components (say, x and y on your circle) to the circle's center.
How to make a 2d world with fixed size, which would repeat itself when reached any side of the map?
When you reach a side of a map you see the opposite side of the map which merged togeather with this one. The idea is that if you didn't have a minimap you would not even notice the transition of map repeating itself.
I have a few ideas how to make it:
1) Keeping total of 3x3 world like these all the time which are exactly the same and updated the same way, just the players exists in only one of them.
2) Another way would be to seperate the map into smaller peaces and add them to required place when asked.
Either way it can be complicated to complete it. I remember that more thatn 10 years ago i played some game like that with soldiers following each other in a repeating wold shooting other AI soldiers.
Mostly waned to hear your thoughts about the idea and how it could be achieved. I'm coding in XNA(C#).
Another alternative is to generate noise using libnoise libraries. The beauty of this is that you can generate noise over a theoretical infinite amount of space.
Take a look at the following:
http://libnoise.sourceforge.net/tutorials/tutorial3.html#tile
There is also an XNA port of the above at: http://bigblackblock.com/tools/libnoisexna
If you end up using the XNA port, you can do something like this:
Perlin perlin = new Perlin();
perlin.Frequency = 0.5f; //height
perlin.Lacunarity = 2f; //frequency increase between octaves
perlin.OctaveCount = 5; //Number of passes
perlin.Persistence = 0.45f; //
perlin.Quality = QualityMode.High;
perlin.Seed = 8;
//Create our 2d map
Noise2D _map = new Noise2D(CHUNKSIZE_WIDTH, CHUNKSIZE_HEIGHT, perlin);
//Get a section
_map.GeneratePlanar(left, right, top, down);
GeneratePlanar is the function to call to get the sections in each direction that will connect seamlessly with the rest of your world.
If the game is tile based I think what you should do is:
Keep only one array for the game area.
Determine the visible area using modulo arithmetics over the size of the game area mod w and h where these are the width and height of the table.
E.g. if the table is 80x100 (0,0) top left coordinates with a width of 80 and height of 100 and the rect of the viewport is at (70,90) with a width of 40 and height of 20 you index with [70-79][0-29] for the x coordinate and [90-99][0-9] for the y. This can be achieved by calculating the index with the following formula:
idx = (n+i)%80 (or%100) where n is the top coordinate(x or y) for the rect and i is in the range for the width/height of the viewport.
This assumes that one step of movement moves the camera with non fractional coordinates.
So this is your second alternative in a little bit more detailed way. If you only want to repeat the terrain, you should separate the contents of the tile. In this case the contents will most likely be generated on the fly since you don't store them.
Hope this helped.