Due to the recent interest in our Collector vs. TerraFlex Webinar, I think it’s time we address datum management, both horizontal and vertical. High accuracy in either software is now attainable. 3D accuracy allows for not only excellent XY values, but also, highly accurate Z values. Datum management to avoid datum shifts is not difficult, but sometimes confusing. Which settings will you need to address for your workflow? If you get it wrong, all your data may be shifted incorrectly.
If you’re just using a phone or tablet with no high accuracy equipment involved, then this subject doesn’t matter much. If you’ve invested in an external receiver to achieve better accuracy, then this is for you. We need to address a few different questions here. As you know, all GNSS data from positioning satellites is transmitted in the standard lat/long geographic coordinates on the WGS 84 datum. What happens to those coordinates after they are received is another story. If you are using a real-time correction source that is in something other than the WGS84 datum, this needs to be addressed. If your geodatabase in GIS is not WGS84, then where will you make that transformation on the data from field to office?
Elevation or Z values are always received from GNSS satellites in Height Above Ellipsoid (HAE) in meters. But what if I want to see my elevation data in Mean Sea Level (MSL)? There are some recent developments on this front. The latest TerraFlex Desktop add-in allows you to set a Geoid transformation on the data when it is returned to the office. Collector does not collect 3D data at this time. However, it will automatically populate an attribute value for elevation, which can then be used in the above model to create a 3D feature class. Now that vertical datums and datum transformations are supported in ArcGIS, you can also convert elevation data from HAE to MSL. The vertical accuracy with Collector video will show you how to do this.