I have pointA and pointB in world coordinates. I want to find the pointC which will be perpendicular to line AB.
Due to my average math skills, I don't know how to find pointC. I searched on google and found that I have to find yaw, pitch and using some formula I can find the pointC at given distance. I followed the solution given in this link but still not able to achieve what I want.
I have started learning threejs couple of weeks back and I know we can rotate object using lookAt() method. So once I know pointC, I will use the lookAt() method to rotate an object.
I am also new in threejs and also tried using angleTo() and axisRotationOnAxis() but due to lack of knowledge I failed.
Any help?
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I am trying to implement a ear clipping algorithm into a program of mine but I am having issues. While that I can get it to work in a lot of situations, I haven't found a good way to check for reflex angles.
I've been looking up ways - every method I've tried to date seems to have angle it won't work for. When I try to find more information, most people's tutorials/work just tell me to "find the reflex angle and test for ear" then describe how to test for ear but not how to get the reflex angle.
Can anyone tell me how to get the proper angle inside the triangle for a concave polygon, or point me in the right direction? Could be an understanding issue with me. Thanks.
Figured out my problem was one of how I was conceiving the issue. I was saying that if the point was outside the polygon it could still be in the polygon without adding in my head the fact I removed the last vertex. Been busting my brains trying to implement ear clipping for a few days and got it wrong at this point - the solution was the basic "check if the center point of the triangle was outside the polygon and mark it as reflex".
I'm currently making a prototype game where the player walks along the isosurface of a collection of moving metaballs. I've already implemented walking along a sphere with a forward and up vector. To extend this to the metaballs I need to be able to query for an arbitrary point the direction to the closest surface and the distance to the closest surface to be able to snap the player back to the surface after I've moved him along the forward vector. I can calculate the direction by taking a weighted average of all vectors but how do I get the distance?
I'm using the 1 / (x*x + y*y + z*z) function with an isosurface of 1 for my metaballs but I would appreciate any generalization so that I can use the same approach for other shapes.
In general, you would just derive your function to get the normal on the surface. Blackpawn has a nice explanation how to do it with your specific case here.
Once you got the normal, move along its direction until you hit the isosurface (this is generic "root" finding).
I am quite new to this, and iv'e heard that i need to get my inversed projection matrix and so on to create a ray from a 2D point to a 3D world point, however since im using OpenglES and there are not as many methods as there would be regulary to help me with this. (And i simply don't know how to do it) im using a trigenomeric formula for this insted.
For each time i iterate one step down the negative Z-axis i multiply the Y-position on the screen (-1 to 1) with
(-z / (cot(myAngle / 2))
And the X position likewise but with a koefficent equally to the aspect ratio.
myAngle is the frustum perspective angle.
This works really good for me and i get very accurate values, so what i wonder is: Why should i use the inverse of the projection matrix and multiply it with some stuff instead of using this?
Most of the time you have a matrix lying around for your OpenGl camera. Using an inverse matrix is simple when you already have a camera matrix on hand. It is also (oh so very slightly at computer speeds) faster to do a matrix multiply. And in cases where you are doing a bajillion of these calculations per frame, it can matter.
Here is some good info on getting started on a camera class if you are interested:
Camera Class
And some matrix resources
Depending on what you are working on, I wouldn't worry too much about the 'best way to do it.' You just want to make sure you understand what your code is doing then keep improving it.
I am in charge of a program that is used to create a set of nodes and paths for consumption by an autonomous ground vehicle. The program keeps track of the locations of all items in its map by indicating the item's position as being x meters north and y meters east of an origin point of 0,0. In the real world, the vehicle knows the location of the origin's lat and long, as it is determined by a dgps system and is accurate down to a couple centimeters. My program is ignorant of any lat long coordinates.
It is one of my goals to modify the program to keep track of lat long coords of items in addition to an origin point and items' x,y position in relation to that origin. At first blush, it seems that I am going to modify the program to allow the lat long coords of the origin to be passed in, and after that I desire that the program will automatically calculate the lat long of every item currently in a map. From what I've researched so far, I believe that I will need to figure out the math behind converting to lat long coords from a UTM like projection where I specify the origin points and meridians etc as opposed to whatever is defined already for UTM.
I've come to ask of you GIS programmers, am I on the right track? It seems to me like there is so much to wrap ones head around, and I'm not sure if the answer isn't something as simple as, "oh yea theres a conversion from meters to lat long, here"
Currently, due to the nature of DGPS, the system really doesn't need to care about locations more than oh, what... 40 km? radius away from the origin. Given this, and the fact that I need to make sure that the error on my coordinates is not greater than .5 meters, do I need anything more complex than a simple lat/long to meters conversion constant?
I'm knee deep in materials here. I could use some pointers about what concepts to research.
Thanks much!
Given a start point in lat/long and a distance and bearing, finding the end point is a geodesic calculation. There's a great summary of geodesic calculations and errors on the proj.4 website. They come to the conclusion that using a spherical model can get results for distance between points with at most 0.51% error. That, combined with a formula to translate between WGS-84 and ECEF (see the "LLA to ECEF" and "ECEF to LLA" sections, seems like it gets you what you need.
If you want to really get the errors nailed down by inverse projecting your flat map to WGS-84, proj.4 is a projection software package. It has source code, and comes with three command line utilities - proj, which converts to/from cartographic projection and cartesian data; cs2cs, which converts between different cartographic projections; and geod, which calculates geodesic relationships.
The USGS publishes a very comprehensive treatment of map projections.
I'd do a full-up calculation if you can. That way you'll always be as accurate as you can be.
If you happen to be using C++ the GDAL is a very good library.
For a range of 40km, you may find that approximating the world to a 2D flat surface may work, although a UTM transform would be the ideal way to go - in any case, I'd advocate using the actual WGS84 co-ordinates & ellipsoid for calculations such as great circle distance, or calculating bearings.
If you get bored, you could go down a similar line to something I've been working on, that can be used as a base class for differing datums such as OSGB36 or WGS84...
I am using a 3D engine called Electro which is programmed using Lua. It's not a very good 3D engine, but I don't have any choice in the matter.
Anyway, I'm trying to take a flat quadrilateral and transform it to be in a specific location and orientation. I know exactly where it is supposed to go (i.e. I know the exact vertices where the corners should end up), but I'm hitting a snag in getting it rotated to the right place.
Electro does not allow you to apply transformation matrices. Instead, you must transform models by using built-in scale, position (that is, translate), and rotation functions. The rotation function takes an object and 3 angles (in degrees):
E.set_entity_rotation(entity, xangle, yangle, zangle)
The documentation does not speficy this, but after looking through Electro's source, I'm reasonably certain that the rotation is applied in order of X rotation -> Y rotation -> Z rotation.
My question is this: If my starting object is a flat quadrilateral lying on the X-Z plane centered at the origin, and the destination position is in a different location and orientation where the destination vertices are known, how could I use Electro's rotation function to rotate it into the correct orientation before I move it to the correct place?
I've been racking my brain for two days trying to figure this out, looking at math that I don't understand dealing with Euler angles and such, but I'm still lost. Can anyone help me out?
Can you tell us more about the problem? It sounds odd phrased in this way. What else do you know about the final orientation you have to hit? Is it completely arbitrary or user-specified or can you use more knowledge to help solve the problem? Is there any other Electro API you could use to help?
If you really must solve this general problem, then too bad, it's hard, and underspecified. Here's some guy's code that may work, from euclideanspace.com.
First do the translation to bring one corner of the quadrilateral to the point you'd like it to be, then apply the three rotational transformations in succession:
If you know where the quad is, and you know exactly where it needs to go, and you're certain that there are no distortions of the quad to fit it into the place where it needs to go, then you should be able to figure out the angles using the vector scalar product.
If you have two vectors, the angle between them can be calculated by taking the dot product.