Download Global Positioning System (GPS) Data Collection Guidelines

GPS QUICK REFERENCE GUIDE
I. Mapping Grade GPS:
• Critical Settings
o Position Mode: Recommended manual 3D mode (requires 4 satellites)
o Minimum Satellites: This guideline recommends 4
o Elevation Mask: It is recommended that a mask of 15 degrees be applied (It may be
appropriate to increase the Elevation Mask when collecting data in valleys or urban areas)
o Signal to Noise Ration (SNR) Mask: Varies from GPS receiver Manufacture. Users should
consult the user manual to obtain the SNR Mask.
o Position Dilution of Precision (PDOP): the user should stop data collection when PDOP is
greater than 6
o Logging interval: Collection rate should be equal to or a multiple of the sampling rate of the
base station use in post-differential correction e.g., 1, 5, 10, 15, or 30 seconds
o Minimum Positions: For Point data this Guideline recommends that the user set the default
data collection rate to one second and the minimum number of positions to 30.
o Carrier Mode: allows a receiver to collect carrier phase data used for surveying purposes.
SHUT CARRIER MODE OFF.
•
Reference System:
o Datum: It is recommended that Datum be North American Datum from 1983 (AKA: NAD
83)
o Projection: New York State Plane
o Units of Measure: Feet
**The Suffolk County GIS Technical and User Committees adopted New York State Plane NAD 83
Feet
•
Mission Planning
o Users Should be aware of Known Satellite Outages, PDOP, and local Obstructions to the sky
and change the receiver settings and plan data collection times accordingly
•
Number of Channels
o The more channels that a receiver has the greater the potential accuracy for the data
collection points will be. This guideline recommends that the receiver have the capacity to
track 12 channels
•
Data Collection
o External Antenna: It is recommended that an external antenna be used when collecting data
in wooded or urban areas and anywhere where obstructions to the sky occur.
o Data Dictionary Design: It is recommended that a Data dictionary be used but not editable in
the field.
o Data Download: The data should be downloaded from the receiver to a computer or network
as soon as possible
o Post Processing: Recommended even when using a real time correction method
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