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Spectra Precision FAST Survey Reference Manual User Manual

Page 256

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Note in the “cut” example above (bottom figure) how the catch point may be closer or farther from the pivot point based

on the slope of the original ground. With flat ground at virtually the same elevation as the centerline of the road, the

catch is found approximately 15 feet from the pivot point in the base of the ditch. But with ground sloping slightly

uphill, it takes a full 30 feet or so to find the catch point. The program helps find the catch quickly by modeling the

surface of the ground with each shot taken. Thus, by projecting the ground slope outward, the program advises the user

how far to go to find the anticipated catch point. Unless the ground slope changes dramatically, the catch point is

usually staked within just a few tries. With GPS, the process is even more automatic, since the ground elevation is being

computed continuously as you walk toward the catch point. No “shot” has to be taken until you are positioned right on

the catch point itself. This next figure shows a cut condition slope stake in 3D. The “catch” is located at the top of the

cut.

Four Methods of Slope Staking

User-Defined

: This is the most commonly used method of slope staking. Here, you simply enter the station, offset

and elevation of the pivot point. Do not enter a minus sign for a left offset as in –25, since the program detects

whether you are left or right of centerline. The only prerequisite is the selection of a centerline file. Cut and fill

slopes are entered in the field.

Point-Defined Alignments:

This method is often used for staking the top of cut for a ditch, particularly a V-ditch.

You can select the centerline by any of the three classic methods of centerline file, a picked polyline on the screen,

or a sequence of points. The vertical alignment can be derived from any picked 3D polyline or from the elevations

on the sequence of points, or you can separately enter a profile. This method is useful for slope staking existing

flow lines, where you simply take two shots at either end, create an alignment by point number, then set the slope

stakes at the user-entered slope ratio.

Design Files

: This is the most “formal” way of slope staking, but typically only applies to uniform, simple road,

drainage ditch or levee projects where the pivot offset positions do not vary from station to station. While all

methods require that a centerline be selected, the design file method additionally requires, at a minimum, a template

file and a profile (vertical alignment). For more complex roads, superelevation files and template lane width

transition files may also be entered. With the exception of the centerline, profiles and simple templates, the other

files are usually created at the office using Carlson Civil, Carlson Roads or TakeOff, and then downloaded onto the

field computer.

Note:

Whenever the Road Design File option is selected, templates can be selected as a single “TPL” file, or

as a series of templates organized as a “TSF” file (Template Series File). The TSF file can be entered within

Road Utilities. If the left pavement lane of a road expanded from 10’ to 20’ for a passing lane, from station

1100 to 1200, you can create two templates, Road1 with the 10’ lane and Road2 with the 20’ lane. Then if you

create the Template Series File shown below, the program will auto-calculate a 15’ left pavement width at

station 1150. This same feature can be accomplished by using one template and applying a Template

Transition File, which instructs on the changing dimensions of portions of a single template. Unlike the

Template Series File, the alternate Template Transition File can only be created at the office using Carlson

Civil, Carlson Roads or Carlson TakeOff.