I confused about this issue. When using a RTK-GPS system do you collect your data on the "Ground" or "Grid"? Also, if you where surveying on the "grid" with a RTK-GPS then switched to a total station to collect a point under thick canopy would you not now have a problem?
You might want to mention what equipment and software you are using, and their definition of "grid". The issue, as far as I know, is that some people consider that a "grid" is the state plane grid, and some manufacturers, might think of the grid being a cartesian coordinate grid vs. spherical coordinates.
we work on grid. when preparing descriptions or drawings, the distances are converted to surface by applying the combined scale factor.
it ain't no big deal to set up the robot and collect data or stake out using grid if you input you combined scale factor into the collector. actually, on a topo of dirt, it's pretty irrelevant as long as you have the correct instrument height elevation in the collector. imho applying the scale factor on a topo of dirt doesn't change the horizontal or vertical location enough to worry about, but if you are tying down hard structures the csf is needed if you are working at grid.
I collect everything on ground unless there is the odd client who wants something on grid. The data collector projects everything to ground so when you set up the robot it's also projected to ground. In the past there were real problems with mixing GPS and total stations. They didn't always play well together.
But there is no way I can speak for your set-up.
If someone wants a grid (which can mean any number of systems) coordinate for some reason I convert it later.
> I confused about this issue. When using a RTK-GPS system do you collect your data on the "Ground" or "Grid"? Also, if you where surveying on the "grid" with a RTK-GPS then switched to a total station to collect a point under thick canopy would you not now have a problem?
We work with both interchangeably. Depends on your software a bit and being aware of your data. You can set up an RTK job to output on ground and then work with your TS at SF 1, or vice versa being to run Grid for both then if ground is needed for the end result deal with it in the office using the CSF. You could also run Grid in the RTK and Ground in the TS then adjust your data together in the office identifying each measurement set for what it is. StarNet mixes data nicely as does TBC etc.
We work on ground. Grid is an imaginary mathematical construct that has no use in the real world - it serves to confuse the best of us and cause endless headaches and confusion. Its a tool for geodesists, not surveyors...IMHO
Ahhh, I love it when someone finally arrives at the point that they realize there is confusion and they would like to put a stop to that confusion (at least for themselves). I am with Moe.
If you worked for me you would do all your work in ground. That way you would learn how to work in ground and you would always know your measurements or layout were ground measurements. If you are working solo and understand how all these measurements and projections work, you can choose either system and make it work fine. This ground/grid thing confuses a lot of people, not the least of which are a lot of surveyors. The best method is to remove the confusing part of it and proceed. When working for me you will work with the ground and it will not confuse any architects, engineers, inspectors, CAD monkeys, survey techs, party chiefs or instrument persons. If the deliverable must be in grid, we will output it that way at the end with the proper notes to make others aware of that (if they choose to read the notes).
I am giving you a touchdown for realizing the confusion exists and an extra point for asking how to remove that confusion!
Good subject
Nobody works on ground. Think about it. If you use a total station you are working on a grid plane perpendicular to gravity at every setup. The distortion to ground truth is so small that it is unoticable for all intents. You can't survey on the ground when the ground is a globe and all surveys are mapped on a grid plane. We are all professional liars. GPS makes us confess and total station lets us gloss it over.
When using a RTK-GPS system do you collect your data on the "Ground" or "Grid"?
You collect data in accordance with the way you software is configured. You define the projected grid in your software. It may be state plane or it may be a grid that approximates the ground with less distortion based on a field calibration or a user define low distortion projection.
Also, if you where surveying on the "grid" with a RTK-GPS then switched to a total station to collect a point under thick canopy would you not now have a problem?
No if your user defined grid is low distortion. Maybe if you grid is state plane depending on your combined scale factor at your given location. As has been mentioned that can be overcome by applying the combined scale factor to your total station observations.
Some learned that in the 70's when mixing grid and ground. We were using Triangulation Stations to get on the SPC system with the idea our coordinates would be good forever, but mixing during the office manipulation always made us wonder what was really in the file. Most chose ground and stuck with it, heck we are not even using the same SPC system that was in place then and lord only knows how many adjustments have been made. The reason for low distortion grids coming into use is so one grid system can be used for everything and that grid is close enough to the surface making the distortion small enough to be insignificant. The need for and the development of those low distortion grids alone should be all the warning needed for the wise to accept that there are more problems with using SPC than constant adjustments. I favor local grids, almost every survey I do is a local horizontal grid at the surface.
jud
Linebender is correct. All the work we do in a GPS is really a grid of some sort projected by the software, in my case I chose a grid that is as "close" to ground distances as I can get it.
Before crews even leave for the field the data collector and office software is set up with the projection that is chosen for the job. After that it isn't touched unless some GIS person wants NAD 27 UTM meters or something which I'll convert for them.
I am actually amazed that this is still being argued. With GPS, the data we collect is Lat./Long plus ellipsoid height. Most of us then use our software to convert it to "State Plane Grid" (usually the accepted format through out the area) for which ever area we are working in, along with a Geoid file which would correct the elevations more closely to those found on the ground. Why would you want to add another conversion to it in the field? Maybe you would need to go outside of your project area to find another monument, say a few miles distant from your project, and that monument was discovered later in the project, and your combined scale factor could have distorted the coordinates enough to cause concern, when there really was nothing to worry about. All of the cad software I know of can easily handle the importation of grid coordinates, yet apply the correct (at least the one you are going with, I hate it when people publish a surface drawing with combined scale factor listed out to 9 or 10 decimals) scale factor for horizontal distances. A lot of our work is doing large tree and topo surveys of land that is to be subdivided, and we usually are involved through out the process of the subdivision, from the original boundary to final platting. Our clients, mostly engineering firms, prefer that our drawings be in grid as they are able to import in aerial photos, GIS maps or whatever that is based on that particular "State Plane Grid", hell you can even import them into Google Earth. That, at least, is my humble opinion.:-/
I doubt it will stop being argued anytime soon. I thought back in the 1970's it was pretty well settled. All real work would be done on the ground and if for some odd reason state plane grid coordinates were wanted then they were produced. Usually a very large mapping project. Then computer systems and GPS came along making in a no-brainer and so easy to work on the ground and all this arguing started up. Oh well.
