Roadway Design Question and Answer Forum
Geopak
Question:
When generating the centerline coordinate list, why does the Northing and Easting
coordinates in COGO sometimes not match the printout for the same station?
Answer:
The problem was created when the chain was first stored in COGO. While we normally report stations
to two (2) decimal places for English projects and three (3) decimal places for Metric projects,
it is inconsistent to the coordinate readout accuracy, which is to four (4) decimal places.
Describing chain -RPBY8- yields two different beginning stations depending on the set station
accuracy.
Note a difference of 0.0026 ft.
Because the Centerline Coordinate List program depends heavily on the beginning station (double precision,
16 decimal places!) and the increment distance to report each coordinate point along the chain, by the
time a desired even beginning station to start the report is reached, the coordinates and station may not
matched what is in COGO and the printout.
Here is the comparison at station 10+00.00 of the same chain, -RPBY8-.
Note a difference of 0.0027 ft in the Northing.
A simple fix is to store the beginning of the chain accurately, e.g. 4+35.12. In this case, since the
beginning station for -RPBY8- is actually 10+00.00, simply restore and restation chain -RPBY8- starting at
station 10+00.00. I have made a copy of the RDY GPK and recreated a chain -RPBY8REV-.
