[OpenLayers-Users] Point in parrallel with line formula

[Chris Adams]

Here is a JavaScript code which will calculate the distance in meters. The points are (lon1, lat1) and (lon2, lat2)

var R = 6371*1000; // m
var dLat = (lat2-lat1).toRad();
var dLon = (lon2-lon1).toRad(); 
var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
        Math.cos(lat1.toRad()) * Math.cos(lat2.toRad()) * 
        Math.sin(dLon/2) * Math.sin(dLon/2); 
var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
var d = R * c;

Also, if you are using Java, you will want to preform all the operations 
from previous equations sent to you from me, using floats or doubles.

newbie wrote:
> Dear Chris, 
>               My data is in Latitude/Longitude. Ok I have used the java
> sample code giving in the exercise. Only thing now I need to confirm is that
> what is distance output in wat format ? Thank you.
>
> Chris Adams wrote:
>   
>> For the second part, you use this equation first, to find 'u':
>>
>> http://local.wasp.uwa.edu.au/~pbourke/geometry/pointline/pointline2.gif
>> (Where (x1,y1)-(x2,y2) is the line, and (x3,y3) is the point)
>>
>> Then, you use this equation:
>>
>> x = x1 + u (x2 - x1)
>> y = y1 + u (y2 - y1)
>>
>> to calculate the new point (x,y)
>>
>> Then you have to use some distance equation, to find the distance 
>> between (x3,y3) and (x,y).
>>
>> Is your data in Latitude/Longitude? or Spherical Mercator? or something 
>> else?
>>
>> newbie wrote:
>>     
>>> Dear Chris,
>>>               So once I have I have decide whether is +1 or -1 then I
>>> must
>>> apply the other formula. So must I still apply the first formula to
>>> decide
>>> +1 or -1 or can I just go to the second formula. Secondly I still cant
>>> really see the implementation of the formula. So is there any example
>>> implementation of this formula cause I dont know to how to get the answer
>>> in
>>> metres? Thank you.
>>>
>>> Chris Adams wrote:
>>>   
>>>       
>>>> +1 means to the left
>>>> -1 means to the right
>>>>
>>>> before calling the 'ccw' function, you'll want to order p0 and p1 so 
>>>> that p0 has the smaller latitude
>>>>
>>>> To get the distance on the left or right, use the formula linked from my 
>>>> second response. It finds the closest point, on the line to the other 
>>>> point, and then you need to take the distance between the two. If you 
>>>> use Pythagorean theorem, it will give you distance in whatever 
>>>> measurement  the projection of your map is in.
>>>>
>>>> newbie wrote:
>>>>     
>>>>         
>>>>> Dear Chris, I am a bit confuse. So the d will be in what measurement 
>>>>> is it meter or km ? Then if is + or - what is the difference too. 
>>>>> Thank you.
>>>>>
>>>>>     Chris Adams wrote:
>>>>>     Here's a C++ function (Should be easy to convert to JavaScript) /*
>>>>>     Taken from Robert Sedgewick, Algorithms in C++ */ /* returns
>>>>>     whether, in traveling from the first to the second to the third
>>>>>     point, we turn counterclockwise (+1) or not (-1) */ int ccw( Point
>>>>>     p0, Point p1, Point p2 ) { int dx1, dx2, dy1, dy2; dx1 = p1.x -
>>>>>     p0.x; dy1 = p1.y - p0.y; dx2 = p2.x - p0.x; dy2 = p2.y - p0.y; if
>>>>>     (dx1*dy2 > dy1*dx2) return +1; if (dx1*dy2 < dy1*dx2) return -1;
>>>>>     if ((dx1*dx2 < 0) || (dy1*dy2 < 0)) return -1; if ((dx1*dx1 +
>>>>>     dy1*dy1) < (dx2*dx2 + dy2*dy2)) return +1; return 0; } >From this
>>>>>     post on GameDev.net
>>>>>     http://www.gamedev.net/community/forums/topic.asp?topic_id=457450
>>>>>     Note it will also return 0 if the point is precisely on the line.
>>>>>     The deals with turn directions, so it depends on the ordering of
>>>>>     the points on the line. To get around this, you'll want to swap p0
>>>>>     and p1, if if p1 is below p0. (If p1's latitude is smaller than
>>>>>     p0's) newbie wrote: > Dear All, > Just say I got a pair of lat and
>>>>>     long p1 and p2 and I draw a line > based on both the points. So
>>>>>     now I want to know if a particular point in the > parallel range
>>>>>     of say 50m either on left or right sides of the line. How can > I
>>>>>     decide this what is the formula please ? >
>>>>>     _______________________________________________ Users mailing list
>>>>>     Users at openlayers.org http://openlayers.org/mailman/listinfo/users
>>>>>
>>>>>
>>>>> ------------------------------------------------------------------------
>>>>> View this message in context: Re: Point in parrallel with line formula 
>>>>> <http://n2.nabble.com/Point-in-parrallel-with-line-formula-tp2742247p2746662.html>
>>>>> Sent from the OpenLayers Users mailing list archive 
>>>>> <http://n2.nabble.com/OpenLayers-Users-f1822463.html> at Nabble.com.
>>>>> ------------------------------------------------------------------------
>>>>>
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