To work in NGVD...

[John Troelstrup]

Probably a very basic question but...

I am working in a county that I have not worked in before and its standard is NGVD.
I have never changed any of my coordinate standards since purchase so a little bit scared to toy with them.

To work in NGVD is it as simple and setting up a new coordinate system where as I leave all the SPC stuff the exact same and then can I choose NGVD as opposed to NAVD?
Can you create coordinate profiles? For instance, this one could be Hernando County.
Thank you,

 

[Shawn Billings]

Likely you do not need to change your coordinate system. Your corrections source and control will determine how to proceed.

If you are using, for example, an RTN, then you will need to translate vertically from your RTN vertical to NGVD29. This can be done using localization or shift.

If you are using your own base and the base is set up on a control point with an NGVD29 height, then there is nothing you need to do.

Over small areas, NGVD29 and NAVD88 will have the same slope from the NAD83 ellipsoid. Large areas, this will not be true as the difference between NAVD88 and NGVD29 change across the country.

Ultimately, to be on NGVD29, you need to tie into an NGVD29 monument, then translate your survey to that observation.

 

[John Troelstrup]

Thank you Shawn.
I have been doing just that.
I am cheating my elevation at the base with the NGVD.
Since I am working off of SPC Grid, there has been no reason to Post Process my daily work as I assume that would end up producing NAVD results after DPOS?

I stay off of the RTN as much as possible.

 

[Shawn Billings]

I assume that would end up producing NAVD results after DPOS?

Yes sir, that is correct.