Orthometric Elevations

Bad Elf Flex Mini: Mean Sea Level (MSL) Elevations in ArcGIS Field Maps

Introduction

Using the Bad Elf Flex Mini and ArcGIS Field Maps for elevations?
You may have noticed inaccurate vertical elevations. That’s because ArcGIS Field Maps records ellipsoidal heights in the ESRIGNSS_ALTITUDE field, while most users need the orthometric elevations (height above mean sea level) of their features.  Orthometric elevations use a geoid (gravity) model, and are the type of elevations typically shown on topographic maps used in engineering, construction, and surveying.

Field Maps does record orthometric elevations in the geometry if the feature class has Z-values enabled, however, they are not visible by default. These elevations use the EGM96 geoid (gravity model).

Alert
The EGM96 geoid is only compatible with the WGS84 or ITRF datums.  It is NOT compatible with NAD83 or other localized datums.  Please take note if you are using RTK corrections with the Bad Elf Flex Mini.

What You’ll Need

To successfully collect offset metadata with ArcGIS Field Maps and the Bad Elf Flex, make sure you have the following:
  1. Bad Elf Flex Mini→
  2. Bad Elf Flex app→
  3. ArcGIS Online License
  4. ArcGIS Field Maps app
  5. iOS or Android tablet/phone

How to Add Orthometric (MSL) Field

Idea
We recommending adding Esri's GPS Metadata Fields if you have not done so already.
  1. Open your data collection map in Field Maps Designer.
  2. Under Forms > Form builder > Form elements, drag and drop Number - Double into the form.

      
      3. Fill out the Display name and Field name parameters.
      4. Save the form.
      5. Select the newly created field in the form to open the Properties window, and select Logic > Calculated expression.

      6.  Enter the following calculation into the form:
Quote
Geometry($feature).z
Idea
The above calculation outputs elevation in meters.  To convert to feet, multiply the above expression by 3.28084.       
      7. Save the form.
Notes
This expression will not be retroactively applied automatically to any previous features in the layer.  Perform a field calculation to apply to previously collected features.

Frequently Asked Questions

Q: What is the difference between ellipsoidal height and orthometric elevation in GIS data?
A: Ellipsoidal Height is the raw height measured by a GNSS receiver above a mathematically defined smooth reference surface (the ellipsoid, such as WGS84). This is what GNSS receivers output by default. Orthometric Elevation (often called elevation or height above mean sea level) is the height above the geoid, which is an irregular model representing the Earth's true gravity surface. Orthometric elevation is typically required for engineering, surveying, and topographic mapping.

Q: Why does ArcGIS Field Maps show inaccurate elevation data when I use my Bad Elf Flex Mini?
A: By default, ArcGIS Field Maps records the raw ellipsoidal height from the GNSS receiver in the Altitude field.

Q: Do I need to enter the pole height to get correct orthometric elevation?
A: Yes, absolutely. To achieve accurate ground elevation, you must measure and enter the pole height (antenna phase center to the ground/feature). 

Need Help?

  1. Email: support@bad-elf.com
  2. Visit: Bad Elf Flex: Configuring ArcGIS Field Maps →
  3. Visit: Field Maps Knowledge Base →
  4. Explore: Bad Elf Flex Documentation →