Everything you need to get the most from Scientific Altimeter
Scientific Altimeter uses your device's built-in sensors combined with authoritative government data to provide accurate elevation measurements:
Location permission is required to access your device's GPS receiver for altitude measurement and to determine your coordinates for USGS elevation calibration. The app only uses location data for real-time measurement and does not store, track, or share your location.
Yes. The app can operate in GPS-only mode without internet connection. Barometer calibration requires internet to access USGS data, but you can also use manual calibration to set a known elevation when offline. Once calibrated, the barometer continues to work without internet.
Accuracy depends on the mode and conditions:
GPS-only: ±10-20 meters typical. GPS altitude is inherently less accurate than horizontal position due to satellite geometry.
Calibrated Barometer: ±1-3 meters in stable weather conditions. Barometric measurements are very precise for relative elevation changes but require calibration for absolute altitude and can drift with changing weather.
Best practices: Use in clear outdoor conditions, calibrate at the start of fieldwork, and recalibrate if weather changes significantly.
The USGS Elevation Point Query Service (EPQS) is a free, public API provided by the U.S. Geological Survey. It returns ground elevation for any location in the United States based on high-quality digital elevation models. This is the same data used by professional GIS applications and scientific research. Learn more at epqs.nationalmap.gov.
GPS readings naturally vary by several meters due to satellite position changes, atmospheric conditions, and signal reflections. This is normal GPS behavior. The app displays real-time readings to help you understand measurement uncertainty. Taking multiple readings and calculating an average provides better accuracy.
Use the data logging feature to record measurements, then export to CSV format. The CSV file includes timestamps, GPS coordinates, altitude readings, and pressure measurements. You can open this file in Excel, Google Sheets, R, Python, or import it into GIS software for analysis.
GPS typically does not work indoors due to building obstruction of satellite signals. However, the barometer works anywhere. You can calibrate outdoors, then move indoors and continue using the barometric altitude measurement. This is useful for measuring building heights or conducting classroom demonstrations.
Barometers measure atmospheric pressure, which varies with both elevation and weather conditions. Calibration sets a reference point so the app can calculate altitude from pressure. Without calibration, the barometric reading shows only relative changes in elevation. With calibration, you get accurate absolute altitude.
Calibrate at the beginning of each field session. If you're working in one area all day with stable weather, one calibration is usually sufficient. If you travel to a new area or notice significant weather changes (such as a passing storm front), recalibrate for best accuracy.
No. Scientific Altimeter does not collect, store, or transmit any user data. All measurements stay on your device. Location coordinates are used only for real-time GPS altitude and USGS calibration queries. No analytics, no tracking, no third-party services. See our Privacy Policy for details.
• Ensure location permission is enabled for the app
• Move to an outdoor location with clear view of the sky
• GPS can take 30-60 seconds to acquire satellites
• Tall buildings and tree cover reduce GPS accuracy
• Ensure you have internet connection
• Check that location services are enabled
• Wait for GPS to stabilize (green indicator)
• USGS data covers US territories only
• Use manual calibration if USGS is unavailable
• Recalibrate at a known elevation point
• Verify you're in an area with good GPS signal
• Check if weather has changed significantly
• Remember GPS altitude has ±10-20m uncertainty
• Take multiple readings and calculate average
We're here to help. Contact us for support, feedback, or suggestions.
Email: [email protected]
Developed by Mark
GIS/Watershed Specialist, UNC Chapel Hill