coordinate systems

[rickh718]

I just installed Civil 3D 2014.

There are two similar listings for Washington State Coordinate Systems.

One is the HARN (HPGN) for NAD-83/91  "HARN/WO.WA-NF"

The other just says Washington North Zone, US FT (or use HARN/WO.WA-NF)

What is the difference between the two? And why have two identical coordinate systems.

[ericcollins6932]

They are both EPSG 2926 but seem to have different datum references.

HARN is referenced to HPGN (replaced by 45 distinct regional HARN datums), Washington North is referenced to Harn/WO (High Accuracy Regional (WO) Network (aka HPGN, NAD83/91)

Reading this, I would suppose that HARN is an older system and Washington North is newer?

One must maintain backward compatibility with older systems so that one can transform between them.

One can test by transforming from one to the other to see if what the magnitude of differences are. They appear to be almost identical, but you will need to research more closely which one you need to use.

[rickh718]

The same names of the Washington State coordinate systems are shown for C3D 2011 and 2014.

There is one more shown in 2014, the one that says Washington only without a date.

There has been an adjustment of the 1983/1991 adjustment twice by the National Geodetic Survey, one called 2007 and another called 2011.

The new CS in C3D 2014 might be one of these, but I would like more clarification

What is EPSG 2926?

[IanMcClain]

There are similar systems setup for California. A 1983 state plane and a HARN state plane referncing the control work done in the 90's. This doesn't adaquately account for the tectonic movement in my area and most people I know just use the 1983 projection and include Epoch information in their survey notes so the the data can be shifted to a common epoch when comparing to other data, (HTDP from NGS was created for this purpose).

The HARN projection just creates more confusion, usualy by someone inadvertantly selecting it and discovering a shift between other data/drawings that is using the 1983 projection. I think of it as two projections of the same model, one just has a shift applied to it. I feel there should only be one projection. The project surveyor should resolve any shift issues due to multiple epochs.

Use whatever works best for you, just be sure to keep good notes.