[OpenLayers-Users] Get point on line?

[Bill Thoen]

Yes, it's a little different for the spherical (Lon/Lat) case. For those 
formulas, check out Ed Williams' Aviation Formulary website at 
http://williams.best.vwh.net/avform.htm. What you're looking for is 
determining waypoint locations, i think.

- Bill Thoen

shane_china wrote:
>
> Bill Thoen wrote:
>   
>> shane_china wrote:
>>     
>>> In openlayers,
>>> I have a straight line with two endpoints. How could I get a point on the
>>> line with given distance to one endpoint? Thank you. 
>>>
>>>       
>> You can find a point anywhere on a line by using a ratio calculation.  
>> Start with the distance to your point divided by the total distance of 
>> your line, then your new X coordinate = the difference between the X 
>> coordinates of the endpoints times the ratio (plus the X coordinate of 
>> the starting line endpoint. For example, if your endpoints are at 
>> coordinates (X0, Y0) and (X1,Y1) then the Cartesian distance is
>>
>> D = sqrt((X1-X0)*(X1-X0) + (Y1-Y0)*(Y1-Y0))
>>
>> Then if the ratio between this and the distance to your point is d, your 
>> new point's coordinates will be:
>>
>> X= X0+(X1-X0)*d/D
>> Y=Y0+(Y1-Y0)*d/D
>>     
>
> So thank you for your answer. Your advise is in X-Y coodinates. Does this
> method also apply to lon lat coodinates? Our earth is a ball, so is it
> different?
> I haven't demonstrate it yet.
>