Grid-ground & software

Excellent post, Loyal. I was just emailing a mutual friend yesterday about how many surveyors think GPS "works in State Plane". We owe it to ourselves to understand what's going on in there, especially if we are going to be using the technology for production. I won't say a surveyor has to be a geodesist, in fact I'm still learning all the time. I certainly didn't know as much when we started using GPS as I do now, but somehow I'm able to follow the work we did more than a decade ago. I say that to say this, I'm not a snob. But I do believe we can and should do better.

One problem with a lot of our current software is the database structure. We're using the same principles of point storage we started using in the 1980's - Point Number, Northing, Easting, Elevation (sometimes) and Description. This has forced us to store our work in some form of Grid because that's generally how we were surveying with transit and chain or theodolite and EDM. It was fine for the time, clearly as it is so ubiquitous. However, more and more GNSS provides a skeletal structure for conventional traverse. GNSS isn't bound by a grid NEZ, it's a global XYZ. With the designed shapes of the ellipsoid and projection surface and the modeled shape of the geoid, terrestrial based points and the measurements on which they are based could be easily tied to the XYZ ECEF model at some epoch in time. From there, the surveyor could project those coordinates into any system he desires and any adjustment - in the past 13 years we've had to work with NAD83(86), NAD83(HARN), NAD83(CORS96) and NAD83(2011). Keeping it all based on one system and simply viewing that data through the lens of a particular adjustment would make things much simpler.

At the core, if all data were stored in some epoch of ITRF, the data could be put into any adjustment, and any coordinate projection at any time. New data could be collected and visualized in some specified projection (State Plane, UTM, LDP, etc.) but in the background stored in a common ECEF XYZ coordinate with epoch.

I hope that's not too much of a departure from what you were saying.

:good: (to both posts).

It's like Baseball...

"Baseball is 90% mental -- the other half is physical."

Yogi Berra

It first hit me doing a control survey. I had one of those long range distance meters and I was reducing each distance to state plane. Checking into a NGS monument on a mountain meant measuring from the valley up from about 3 miles away.

I was also measuring back and closing out my angles. Well I just couldn't make the two distance shots match. The one from the valley was .5' shorter. I finally realized they were both correct but I had two such different reference elevations that the higher one gave me a longer distance.

I needed to mean the two shots and then work it "down" to state plane. It did make it much easier to understand GPS when I finally started using it (all those years running state plane traverses with a T2 and that HP distance meter). Nothing like hand calculations to give you perspective.

Mighty

Now that is a FACT!!!

The world got roundish pretty fast once we got those EDM things.

Back in the 1970s measuring 25-50k foot shots with an AGA-76/78, and cranking angles with a T2, was a whole nuther ballgame. I wish that I had a dollar for every NAD27 State Plane Coordinate that I ever calculated (or set).

I seems like I set a rebar at every 500 ft. State Plane Grid intersection in Northern Nevada at one time or another.

Loyal

:good:

Mighty

Central Nevada for me, T2, HP distance meter, helicopter with a crazy Nam vet, and 1200 sq miles of mapping to set panels for. MX missile project.

Boy does that bring back some memories....T2, electrotape, telerometers, crazy Nam helicopter pilots...it just doesn't get better than that! Reducing and calcin your traverse in SPC by hand....ground to grid becomes reality...

Pablo B-)

ECEF XYZ

All my GPS stuff last 15 years because that's how Trimble software does it.

People wonder what It would be like if GPS goes down. I know. I liked it back then and now there's all this good control out there. Be kind of fun actually

The good part was taking off a USC&G 1st order point and tieing in a USGS electronic traverse point i.e. Leave-ET and being 13 feet off in closure after 120 miles of traverse. Traversing back just to prove your work within 1:50,000. Now we have OPUS with a .09cm with 2 hrs. observation time....Old control surveyors can only think they have died and gone to heaven!!!

Pablo B-)

AMEN!

Really having a good database (GIS?) for the positional data ECEF XYZ and epoch is the way to go. The way Autodesk updates their software you would be nuts to archive your geodetic data like that.

I cannot stand trying to manage geodetic data in CAD.

It is also very difficult to find objective reviews of geodetic software. A lot of software gives some sample workflows that show how to perform a particular function but don't really explain the geodesy, potential pitfalls. assumptions made, or shortcuts take. Most salespeople don't know enough to answer questions on this level either (not blaming here, just stating a fact). Any purchase these days typically requires a high quality training effort by a third party entity that won't gloss over flaws in the software.

Like Loyal alludes to many of us just have access to what we have and need to make lemonade from lemons.

Hardware and software are expensive and now more than ever integrating competing brands is troublesome. Companies invest $$$$ in a particular brand and it is hard to switch once they get you.

Drafting packages for surveying don't need to be elaborate, surfacing is the likely exception.

Geodetic packages for data adjustment and management are far more critical in my view... and more difficult to evaluate.

I would like to see some wish lists for geodetic packages and common gripes.

Thank God for RINEX!