Using NAVD 88 vertical datum in the Reality Engine
Overview
A few months ago, Site Scan for ArcGIS released the option to use NAVD 88 vertical datum for processing in the Reality Engine. NAVD 88 can offer improved absolute vertical accuracy when using State Plane or other foot-based coordinate systems in North America. Therefore, we recommend using NAVD 88 for these coordinate systems.
To make this change easier, NAVD 88 is automatically assigned in the user interface as the vertical datum when choosing a State Plane coordinate system for either a project or GCP set.
What's changing?
Over the coming weeks, the Reality Engine will be set as the default processing engine for all projects using a State Plane coordinate system.
I use a State Plane coordinate system. What do I need to do?
When the change is released, you will notice a new prompt in the user interface for projects and GCP sets that are in a State Plane coordinate system: use NAVD 88 vertical datum. We recommend that you switch to NAVD 88 vertical datum on these projects and GCP sets so you use the recommended configuration.
You can switch to NAVD 88 at any time - even today, before the Reality Engine is set as the default engine for these projects.
Are there any downsides to using NAVD 88?
You might be wondering how this will impact your ongoing projects with existing data that was processed with the Legacy Engine. Since EGM96 and NAVD 88 represent different height models, missions processed using EGM96 vertical datum and later with NAVD 88 vertical datum may not vertically align. This can cause erroneous results if performing analysis on the products.
If your work relies on comparisons between missions, the missions you are comparing should be processed with the same vertical datum. Therefore, the recommendation is that if you have prior missions processed with the Legacy Engine in EGM96 you should reprocess the mission in the Reality Engine using NAVD 88 (both for your project and ground control, if you are using GCPs). This will allow you to make more reliable volumetric comparisons with future missions processed in the Reality Engine as NAVD 88 should represent the more accurate model when processing with a State Plane coordinate system.
Learn more about the Reality Engine rollout here.
FAQs
Q: Can I switch to NAVD 88 before the Reality Engine is set as the default engine for projects in State Plane coordinate systems?
A: Yes, you can switch to NAVD 88 today and begin processing with the Reality Engine. This will reduce the number of warnings that you see in your projects once the Reality Engine change is released.
Q: Is NAVD 88 supported in the legacy engine?
A: No, it is only supported in the Reality Engine. If your projects or GCPs are set to NAVD 88 and you process in the legacy engine, EGM96 will be substituted.
Q: Can I still process my mission in a State Plane coordinate system with EGM96 Geoid vertical datum in the Reality Engine?
A: Yes, but results are not guaranteed. If a transformation is required (for example, if your GCPs are in a different horizontal or vertical coordinate system than the project), it’s likely that processing will fail.
Q: How do I know whether I should use NAVD 88?
A: NAVD 88 should be used alongside State Plane horizontal coordinate systems. Site Scan will prompt you to switch to NAVD 88 when it is the recommended vertical datum pair for your horizontal coordinate system. These prompts, when applicable, will appear in the project output settings, the Edit GCP Set menu, and the processing menu. In addition, Site Scan will automatically set NAVD 88 as the vertical datum when you choose a State Plane horizontal coordinate system.
Q: Can I use NAVD 88 with custom coordinate systems?
A: It is not recommended to use NAVD 88 with custom coordinate systems.
Q: Once the Reality Engine is set as the default for my project, can I switch back to the legacy engine?
A: You can still revert to the legacy engine for a limited time, but we ask that you let us know why the Reality Engine didn’t meet your expectations. If you haven't already, please fill out the survey or contact Technical Support.