1. All crew members using the GPS equipment for timber sale preparation
shall be trained in its use. It is important that users have a basic
understanding of how GPS works before collecting field data.
2. All positional fixes must be differentially corrected to a
reference/base station that is no farther than 500 kilometers
(300 miles) away. Position fixes collected by the remote GPS receiver shall
be collected under the following conditions:
- a Position Dilution of Precision (PDOP) no greater than 6.
3. The reference/base station shall be of a third order (or better), NAD 83 datum position.
4. Position fixes shall be collected while moving around
the perimeter and shall be collected at a time interval that will accurately define
the perimeter of the traverse. A 5 second interval is suggested for a walk
file, however if moving more rapidly a 1 second interval may be appropriate. Loss
of position fixes (signal) for a short duration while moving in a straight
line is acceptable, however position fixes must be received while moving
through all turning points inorder to portray the true representation of the
traverse.
5. Only 3-D positions that are differentially corrected will be used for
area determination. A computer display or plot of the file should show
positional fixes lying one after another in a relative sequential/pattern,
defining the perimeter of the traverse. There should be only
slight irregularities (jumping from side to side) of positional fixes,
if some of these are outliers (do not represent the traverse) they should
be edited from the file. A computer display or large scale plot of the data
should be reviewed by the person who collected the data and it should be
reviewed for the following:
- consistency of data collection (look for a smooth
string of fixes).
At this time if the reviewer is confident that the data collected
meets the above standards, an area calculation can be performed. This calculation
shall be made using NAD 83 datum.
6. If the established standards are not met, it will be necessary
to recollect the data. Data for a portion of a traverse or in the
case of a large traverse, may be collected at different dates and times as long
as it is collected while moving in the same direction as the origional
traverse.
7. The following information will be kept as part of the final record:
- the corrected data file containing the differentially corrected positional fixes in NAD 83 datum.
Please send Comments to: Tony Jasumback, Missoula Technology Development Center, USDA Forest Service or DG: A.Jasumback:r01a
- a minimum satellite elevation angle of 15 degrees.
- a minimum signal level of 6, or the manufacturer's recommended level for good signal quality.
- in the 3-D manual mode.
- large spacing between points. Large spacing would
indicate loss of signal and the possibility of missing positional
fixes at critical turning points that would define the traverse.
- the polygon should resembling the traverse walked
in the field.
- a plot of the traverse at 1:24,000 scale in the current (NAD 27) datum. This is because all of our primary base
series maps are displayed in the NAD 27 datum.
- the date and name of the person who collected the data.
- the name of the reference/base station used for
the differential corrections.
- the method used for area calculation (software).