Hi Khurram
The algorithm for lat/long to linear can be found on the Ordnance Survey
website (www.ordsvy.gov.uk) It is in a pdf called "A Guide To British
Coordinate Systems" - and theres a spreadsheet that implements the
algorithm. Its OSGB but the algorithm is universal. You can replace the
false orgins, scale factor etc to fit your required coordinate system.
There follows a VB implementation of a circles intersection algorithm - the
clsPoint referred to is just a simple class (which could be a type) storing
an x and y.
HTH
Rgds
Paul
'Checks for intersections between two circles
'and then draws one or two points
'NB
' Matrix used to perform transformation
' -- -- -- --
' | cos_t sin_t | | c2x |
' | -sin_t cos_t | * | c2y |
' -- -- -- --
Public Sub CalcIntersectionOfCircles(ByVal pt1 As clsPoint, _
ByVal Rad1 As Double, _
ByVal pt2 As clsPoint, _
ByVal Rad2 As Double, _
ByRef intersectpt1 As clsPoint,
_
ByRef intersectpt2 As clsPoint)
Dim delta_x As Double
Dim delta_y As Double
Dim c1x As Double
Dim c2x As Double
Dim c1y As Double
Dim c2y As Double
Dim distCenters As Double '/* distance between the centers */
Dim X As Double '/* used for checking */
Dim Y As Double
Dim R As Double
Dim diff As Double
Dim offset_x As Double ' /* the offset's to move to the origin */
Dim offset_y As Double
Dim t As Double '/* t is the angle between the second center and the
horizontal after move to the origin */
Dim tan_t As Double
Dim cos_t As Double
Dim sin_t As Double
Dim xLeft As Double
Dim yBelow As Double
Dim xint As Double
Dim yint1 As Double
Dim yint2 As Double
Dim p1x As Double
Dim p1y As Double
Dim p2x As Double
Dim p2y As Double
Const M_PI As Double = 3.14192654 'Better value may be available
Const PROC_NAME = "CalcIntersectionOfCircles"
On Error GoTo ErrorHandler
'Extract input params
c1x = pt1.X
c1y = pt1.Y
c2x = pt2.X
c2y = pt2.Y
delta_x = c2x - c1x
delta_y = c2y - c1y
distCenters = CDbl(Sqr(((delta_x * delta_x) + (delta_y * delta_y))))
If distCenters > 0 Then
'
' Assume that the first circle center lies on the origin and the
second lies on the x axis dist
' Centers from the origin.
' Calculate the intersections for the new configuration using rad1,
rad2 and distCenters
'
'X = (Rad1 - Rad2 + distCenters) / (2 * distCenters)
'Y = Sqr(Rad1 - X)
' ie ve And -ve ' PC note - not being used?
'*/
'
'xint = cdbl((((Rad1 * Rad1) - (Rad2 * Rad2) + (distCenters *
distCenters)) / (2 * distCenters)))
X = (Rad1 * Rad1) - (Rad2 * Rad2) ' Using x as a temporary storage
and splitting evaluation over 3 lines
Y = X + (distCenters * distCenters)
xint = CDbl(Y / (2 * distCenters))
X = (Rad1 * Rad1) - (xint * xint)
If X > 0 Then
yint1 = CDbl(Sqr(X))
yint2 = 0 - yint1
'
'/* work out the angles for the transformation */
If (delta_x <> 0) Then
t = Atn(delta_y / delta_x)
If (delta_x > 0) Then
t = (2 * M_PI) - t
If (t > (2 * M_PI)) Then
t = t - (2 * M_PI)
End If
Else
t = M_PI - t
End If
sin_t = sIn(t)
cos_t = Cos(t)
Else
cos_t = 0
If (c2y > c1y) Then
sin_t = -1 '/* t is 90 degrees */
Else
sin_t = 1 ' /* t is 270 degrees */
End If
End If
'/* Rotate the second center about 0,0 */
p1x = (xint * cos_t) + (yint1 * sin_t)
p1y = (0 - (xint * sin_t)) + (yint1 * cos_t)
p2x = (xint * cos_t) + (yint2 * sin_t)
p2y = (0 - (xint * sin_t)) + (yint2 * cos_t)
'
' /* and then move them from the origin by c1x, c1y */
p1x = p1x + c1x
p1y = p1y + c1y
p2x = p2x + c1x
p2y = p2y + c1y
intersectpt1.X = p1x
intersectpt1.Y = p1y
intersectpt2.X = p2x
intersectpt2.Y = p2y
End If
End If
CalcIntersectionOfCircles_Cont:
Exit Sub
ErrorHandler:
Call mclsErrHdlr.HandleError(MODULE_NAME, MODULE_REVISION, PROC_NAME, _
ERROR_CATEGORY_HIGH, sParameters, sScene)
Resume CalcIntersectionOfCircles_Cont
End Sub
Paul Crisp
Syntegra
Direct: 0191 461 4522
Mobile: 0776 414 3762
Fax: (0191) 461 1959
Innovation Place Metro Riverside Park
Delta Bank Road Gateshead Tyne & Wear NE11 9DJ
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
Sent: 07 January 2002 22:05
To: [EMAIL PROTECTED]
Subject: MI-L Lat/long to linear cord.
Hi all,
I like to convert Mapinfo lat/long cordinates into linear cordinate system
say cartesian cord, and vice versa. I need to get the pints of intersection
between two circles with a given radius and ceneroid. I was thinking to
solve it in cartesian cordinate by using circle equattion, instead of doing
it graphically in mapinfo. Once I can do that I will then easily map it
with the respective data columns. Please let me know any algorithum to
perform the conversion. OR if its not a good idea.
Thanks,
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