I have an alignment i.e. Start station (POT) and end station (PT) and each are assigned coordinets (northing and eastings.)
Using this alignment, how do I calculate the station and offset for a given Northing and easting?
Geometry.
Specifically Coordinate Geometry. Often called "COGO."
Take a survey class. This is taught in the first semester.
Any data collector should do this as well as any CAD program.
> I have an alignment i.e. Start station (POT) and end station (PT) and each are assigned coordinets (northing and eastings.)
> Using this alignment, how do I calculate the station and offset for a given Northing and easting?
A line from the given cords must be calculated to intersect the alignment at a right angle. The length of that line is the "offset". The distance from the Start Station to that intersection is used to calculate the "station". This is basically the solution for a right triangle.
If your line is deined by points a and b, and you have your surveyed point c.
Calc difference in bearing between ab and ac. (angle)
Calc length of triangle side ac. (hypoteneuse)
The offset and station can be calced using sin or cos of the angle multiplied by the hypoteneuse.
> I have an alignment i.e. Start station (POT) and end station (PT) and each are assigned coordinets (northing and eastings.)
> Using this alignment, how do I calculate the station and offset for a given Northing and easting?
calculate the coord of the radius point
inverse to your unknown
subtract the radius distance and you have the offset
use the difference in bearings to calc the delta angle
calc the length of curve
add/subtract curve length for station
if that befuddles you get a government job.
(apologies to the public servants)
Thanks to all.
I know that any good total station or data collector can do this operation for you, but I am trying to create a report that can calculate the data automatically in excel.
Thanks for the help.
Disco
I've done this for simple line offsets in Excel.
I haven't done an alignment, e.g. a combination of tangents and curves, that would be a lot more complicated.
The basic procedure...
1. Assume the southerly end of the line is N5000 & E10000
2. Assume the northerly end of the line is N5200 & E10080
3. Assume the point to offset is N5128 & E10025
Step 1. Calculate the inverse from south to north: N 21°48'05" E ~ 215.40'
Step 2. Calculate the inverse from south to offset point: N 11°03'05" E ~ 130.42'
Step 3. Right or Left? It can be seen that the bearing from south to offset point is left of the bearing from the north point, therefore the offset is to the left.
Step 4. Calculate the difference between the bearings: 10°45'00"
Step 5. Sin 10°45'00" * 130.42 = 24.33' (offset).
Step 6. Cos 10°45'00" * 130.42 = 128.13' (distance along the line from the south).