Bad Elf Flex: Ortho Everywhere - Orthometric Height Elevations in ArcGIS

Bad Elf Flex: Ortho Everywhere - Orthometric Height Elevations in ArcGIS

Problem

If you’re using your Bad Elf Flex with RTK via NTRIP in combination with ArcGIS Field Maps or QuickCapture, you may have faced obstacles when attempting to record accurate vertical heights.  That’s because ArcGIS field products store all elevations recorded with the Bad Elf Flex using the EGM96 geoid. Even though this is fine for situations involving only horizontal measurements or SBAS, EGM96 is not the correct orthometric elevation model for advanced scenarios involving RTK corrections for survey-grade accuracy.  Instead, you need to be recording your elevations with the GEOID18/12B geoids used with the NAVD88 vertical datum in North America.  Up to this point, this required workarounds.

Solution

Bad Elf now offers the ability to record the correct elevation in both the attribute table and geometry of ArcGIS Online features through a simple workflow.  Please ensure that both your software and firmware are updated before beginning. Next, optionally add Bad Elf field attributes by copying the Bad Elf Ortho Everywhere existing layer on ArcGIS Online. After, select “Flow Points to Third Party App” under the “Data Collection” menu.   Turn on auto-flow and you can now overwrite ArcGIS Field Maps features with correct elevation data by logging a point on the Flex before submitting forms.

First, to update the Bad Elf Flex app, simply search for it in your app store of choice and check to see if a download is available.  Update the firmware on the receiver by either downloading it from this page, or updating it in the app (requires firmware version 1208).  

To store orthometric (Mean Sea Level(MSL)/GEOID) heights in the attribute table, please add “badelf_final_ortho_height_m” (double), “badelf_ortho_model” (string), and “badelf_antenna_height_m”(double) as fields to your data collection layer.  These will automatically be overwritten when a point is sent to ArcGIS.  Optionally, add some other fields like “badelf_datum” if they are of interest.  The easiest way to do this is by simply copying our existing layer when creating a new layer on AGOL or ArcGIS Pro, or by using our ArcGIS Pro toolbox.  Note:  ESRIGNSS_ALTITUDE will be the ellipsoidal height, NOT the MSL.

When ready to collect, open the Bad Elf Flex App and select “Flow Points to Third Party App'' under the “Data Collection” menu. Please check the boxes to verify the antenna height, orthometric height model, and ArcGIS field app. By default, “Ellipsoidal” will be used as the height model.  If you’re located in North America and are not sure which model to use, we typically recommend USGG2012 and GEOID18 for SBAS and RTK modes respectively. Under “Orthometric model”, you can also choose whether or not to subtract the antenna height when updating points in ArcGIS.  Leaving this feature on would require leaving the antenna height at 0 on ArcGIS, and only setting heights on the Bad Elf Flex app.  If enabled, a reminder to only configure the antenna height on the Bad Elf side of things appears on the receiver upon boot up.

Once all of the checkboxes in the “Flow Points” checklist are green, tap “Turn on auto-flow”.  You can now either switch views over to your ArcGIS field app of choice, or go into split screen mode with both open.  If using split-screen mode, press back to go to the data collection menu, then enter the standalone logging checklist.  Verify all boxes are checked under “setup”.

In ArcGIS Field Maps or QuickCapture, check your profile to verify your Bad Elf Flex is being used as your location provider, that its antenna height is set to 0 (if aforementioned setting is enabled), and that a location profile is being used if your collection layer is using a different datum than your Flex.  ArcGIS layers are WGS84 by default, so if using RTK, we recommend reprojecting the layer into NAD83(2011).  If this isn’t possible, please use a location profile, but note this may result in a 1 to 2 foot offset horizontally, and does not perform a transformation vertically.

Once you’re ready to record a point, tap the “+” in the bottom right to record a point like normal.  When you have the form open, either record a point on the Bad Elf Flex app or on the receiver itself.  The point will overwrite the geometry of the ArcGIS point and any custom fields in the feature.  Fill out any remaining fields on the form and submit to save the point.  

Any custom attributes in the layer will now be saved and recorded, and the geometry will reflect the relevant orthometric height model (MSL) of the correction mode the Flex was in at the time of recording.  This would be GEOIDxx(NAVD88) for NAD83(2011) used by most North American RTK services.

To recap, once the layer and settings are configured, the process to store correct elevations is quite simple.  First, boot up the receiver and the Bad Elf Flex app.  Next, fill out the “Flow Points to Third Party App” checklist under the “Data Collection” menu and turn on auto-flow.  Open Field Maps or QuickCapture and use it as you normally would until you’re ready to submit and save a point.  Before you submit, record a point on the active Flex project by either logging on the Bad Elf Flex app or directly on the receiver.  Once the Flex beeps, it’ll overwrite the point data to reflect the more accurate information from the Flex.  Tap submit to save and continue saving points on the Flex before submitting forms.  

Let us know if you have any questions!


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