FastRTK

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Version 6 · Currentdocs/getting-started/base-coordinates

Setting Base Coordinates

Accurate base station coordinates are essential for RTK positioning. This guide covers all methods for establishing your reference position.

Why Coordinates Matter

Your base station broadcasts corrections relative to its known position. If the base coordinates are wrong:

  • Relative accuracy is preserved (points are precise relative to each other)
  • Absolute accuracy suffers (entire dataset is shifted from true position)
Coordinate Method Absolute Accuracy Best For
Survey-grade known point Centimeter Permanent installations
OPUS/PPP processing 1-2 cm New permanent sites
RTK from CORS network 2-5 cm Quick setup with network access
Averaged position 1-3 meters Relative work only

Method 1: Known Coordinates (Best Accuracy)

If your antenna is placed over a surveyed control point:

  1. Navigate to Settings > Position
  2. Select Enter Known Coordinates
  3. Enter your coordinates:
    • Latitude/Longitude in decimal degrees, OR
    • State plane coordinates, OR
    • UTM coordinates
  4. Enter ellipsoid height (not orthometric/elevation)
  5. Save and restart the NTRIP caster

[Antenna Height]

Coordinates must be for the antenna reference point (ARP), not the ground mark. Add the measured antenna height to your mark elevation.

Method 2: OPUS Processing (Recommended for New Sites)

Use RINEX post-processing for sub-centimeter accuracy at new installations.

Step 1: Collect RINEX Data

  1. Set an approximate position (use Method 4 temporarily)
  2. Let the base station collect RINEX data for minimum 2 hours (4+ hours recommended)
  3. Download the RINEX observation file from the dashboard

Step 2: Submit to OPUS

  1. Go to NGS OPUS
  2. Upload your RINEX file
  3. Enter your email address
  4. Select your antenna type and height
  5. Submit for processing

Step 3: Apply Processed Coordinates

  1. Receive results via email (typically 5-15 minutes)
  2. Use the NAD83(2011) coordinates from the report
  3. Enter these coordinates using Method 1 above

Detailed RINEX processing guide →

Method 3: RTK from CORS Network

If you have access to a state or commercial CORS network:

  1. Configure a relay mountpoint to connect to the external CORS
  2. Navigate to Position settings
  3. Select Set from RTK
  4. Wait for RTK fix (typically less than 1 minute)
  5. Once fixed, record and save the position

This provides 2-5 cm accuracy depending on distance to the nearest CORS station.

Method 4: Averaged Position (Quick Start)

For temporary setups or when absolute accuracy isn't critical:

  1. Navigate to Settings > Position
  2. Select Average Current Position
  3. Set averaging duration (longer = better):
    • 1 minute: ~3 meter accuracy
    • 5 minutes: ~2 meter accuracy
    • 15 minutes: ~1.5 meter accuracy
  4. Click Start Averaging
  5. Wait for completion, then save

[Accuracy Limitation]

Averaged positions provide only meter-level absolute accuracy. This is suitable for:

  • Temporary field work where relative accuracy is sufficient
  • Initial setup before processing RINEX for final coordinates
  • Testing and training purposes

Not suitable for permanent installations or work requiring absolute accuracy.

Verifying Your Coordinates

After setting coordinates, verify your setup:

Check for RTK Fix

  1. Connect a rover receiver
  2. Verify it achieves RTK Fixed solution
  3. Confirm position accuracy in the rover

Compare to Known Point

If you have access to a nearby control point:

  1. Occupy the known point with your rover
  2. Compare rover position to known coordinates
  3. Differences should be within RTK accuracy (1-3 cm)

Coordinate Reference Frames

For United States Users

  • Primary: NAD83(2011) epoch 2010.0
  • Use OPUS for best results
  • Orthometric heights via GEOID18

For International Users

  • Primary: ITRF14 or WGS84
  • Use AUSPOS or other PPP services
  • May need coordinate transformation for local datums

Coordinate transformation guide →

Next Steps