Thanks to everyone for their help with finding the nearest point. I finally
ended up using a function provided by David Haycraft. Because I was
searching in feet across a short area, I had to modify the function
slightly. First, I had to change all units to "ft". Second, in the strsql
statement, I changed the str$ conversions to Format$ conversions. This was
necessary to preserve the precision on my Lat/Lon coords. The modified
function is below. It works wonderfully!
Thanks again!
Dietrich
'---------------------------------------------------------
'Function Nearest
' Returns the name of the closest object in a search table
' Input parameters
' strTable: name of open search table
' strTargetCol: name of column containing feature names
' fltXC,fltYC: Coordinates of where to center the search
' fltRadiusMin: the initial search radius in ft
' fltRadiusMax: the limiting search radius in ft
' Output parameters
' strItemName: Name of closest target feature
' fltDist: distance in ft to closest target feature
' fltXT,fltYT: centroid of closest target feature
'
' By:
'David M Haycraft
'Information Analysis Associates Pty Ltd
'1 Cumming Place, Wanniassa, 2903
'Aust Capital Territory, Australia
'A MapInfo Technology Partner
'David M Haycraft [[EMAIL PROTECTED]]
'----------------------------------------------------------
Function Nearest$ ( ByVal strTable as string, ByVal strTargetCol as string,
ByVal fltXC As Float, ByVal fltYC As Float,ByVal fltRadiusMin As Float,
ByVal fltRadiusMax As Float,
strItemName As String, fltDist as float, fltXT as float, fltYT as float) As
Logical
Dim fltRadius as Float
Dim fltTemp As Float
Dim strSql as string
Dim n as integer
Dim aliCol as alias
' init
set distance units "ft"
Set Format NUMBER "9,999.9"
fltRadius=fltRadiusMin
' build ID col ref
aliCol="~temp."+strTargetCol
' Select all of the objects within fltRadius ft of fltXC,fltYC
' If there's nothing there, then double the radius and try again.
' Repeat until something is found, or radius exceeds limit
n=0
while (n=0) and (fltRadius<=fltRadiusMax)
' create and execute sql statement to search within a circular buffer
region
strSql="Select * from " + strTable + " Into ~temp NoSelect " +
"Where " + strTable +".Obj Within CreateCircle(" +
Format$(fltXC,"###.######")+","+Format$(fltYC,"###.######")+","+str$(fltRadi
us)+") "
Note "strsql = " + strsql
run command strSql
' get size of result set
n=TableInfo(~temp,TAB_INFO_NROWS)
if n=0 then
' nothing selected - double the radius for the next search
fltRadius = fltRadius * 2
end if
wend
' Test to see if there was anything selected
If n = 0 Then
Nearest$ = False
Exit Function
End If
' Find closest feature in selection collection
fltDist=Distance(0,0,180,0,"ft")
Fetch first from ~temp
while not EOT(~temp)
' get the distance to the selected object
fltTemp = Distance(fltXC, fltYC, CentroidX(~temp.obj),
CentroidY(~temp.obj),"ft")
' is this closest so far?
If (fltTemp < fltDist) Then
' replace feature details
fltDist = fltTemp
strItemName = aliCol
fltXT=CentroidX(~temp.obj)
fltYT=CentroidY(~temp.obj)
End If
fetch next from ~temp
wend
'close table ~temp
' return success
Nearest$ = True
End Function
'---------------------------------------------------------
Dietrich Kastens
(785)843-7789 Home
(785)626-4600 Mobile
[EMAIL PROTECTED]
www.kastensinc.com
_______________________________________________________________________
List hosting provided by Directions Magazine | www.directionsmag.com |
To unsubscribe, send e-mail to [EMAIL PROTECTED] and
put "unsubscribe MapInfo-L" in the message body.
