RE SH 121 Gas Line points (3)
Below is from our surveyor; it appears we are using the exact same
data, but one does not use the conversion while the other does. To go
from one to the other, one would divide or multiply by the conversion
factor accordingly. We are converting your points now, and adding them
to our file. They should fall exactly where they should now.
Below is our Basis of Bearings statement which shows the combined scale
factor we used to convert grid coordinate values to surface coordinate
values. We used the scale factor that was used on the Freeport Parkway
project. We took one of the City’s coordinate values on a CP shot they
made and multiplied it to that scale factor and it came up within a
couple of hundredths. Likewise, if you were to take our coordinate value
and divide by the scale factor you would come up within a couple of
hundredths of their coordinate value. It appears that the City’s
coordinates are grid.
Bearings of lines shown hereon refer to Grid North of the Texas
Coordinate System of 1983 (North Central Zone; NAD83(CORS96) Epoch
2002.00) as derived locally from Western Data Systems Continuously
Operating Reference Stations (CORS) via Real Time Kinematic (RTK)
methods. An average Combination Factor of 1.000126161 was used to scale
grid coordinates and distances to surface. All coordinates shown are
surface.
Casey McBroom, P.E.
Project Engineer
17304 Preston Road, Suite 1340
Dallas, Texas 75252
214.461.9867 Phone
972.900.5733 Mobile
214.461.9864 Fax
cmcbroom@tnpinc.com <mailto:cmcbroom@tnpinc.com>
From: Keith Marvin [mailto:KMarvin@coppelltx.gov]
Sent: Friday, September 13, 2013 11:09 AM
To: Casey McBroom
Cc: Chris Schmitt; Michael Garza; Scott Latta; Kevin Rubalcaba
Subject: FW: SH 121 Gas Line points
Casey,
See the attached point file. We believe that TNP is using a different
coordinate system than we use, and that is causing this discrepancy. If
you are aware of this, and are doing it intentionally to make our
drawings work with the SH 121 widening project, then we can apply some
sort of conversion to our data collection to rectify the situation.
If this is an inadvertent use of a different system, then we will ask
you to correct the drawings to shift your work into the appropriate
coordinate system.
Keith Marvin, P.E.
City of Coppell
972-304-3681
From: Kevin Rubalcaba
Sent: Friday, September 13, 2013 11:04 AM
To: Keith Marvin
Cc: Scott Latta
Subject: SH 121 Gas Line points
These include the most recent points we took today.
-kevin