Trimble Business Center

This week I have been working with a customer relating to some questions that they raised relating to "Managing Point Data" in BC-HCE and SCS900 / Siteworks. The question arose because they were using v3.92 of BC-HCE and were having issues when they resolved Conflicts relating to Site Calibration changes that created a chain reaction that resulted in physically moving Control Point and Stakeout Points because of an apparent Coordinate System Change.

When we tracked back, we found that the issue they were experiencing has been resolved in BC-HCE since the version they were using, however the discussion led me to look deeper into Point Types that exist in BC-HCE and Best Practices to adopt while Importing or Creating Point Data for Control, Stakeout or from survey / site positioning work to minimize any likelihood of problems on projects.

I enclose the Doc here for anyone that may be interested - as a summary these are the Highlights

The two main Point Types created in BC-HCE are Grid Only Points and Grid Points. They are represented on screen differently and have different properties. Grid Only Points are lightweight objects that cannot be moved by a Coordinate System Change whereas Grid Points are heavier more Survey Oriented Points that can be derived from multiple coordinates (N,E,Z, Local or Global Coordinates). In the doc I explore the properties of each, how to create each type and how each type will react to Coordinate System Changes. I also explored SCS900 Office Control, Field Control and Stakeout Point data as well as Site Calibration DC and CAL files to try and drive clarity in use.

Through this process I draw some conclusions and recommendations for development going forwards, but also provide some Best Practice input for you as users of SCS900 and BC-HCE.

I hope that you may find this helpful

Here is the Link - Click Here

Alan

Hi Alan

I ran into this issue today and fortunately your document highlights the issue perfectly! So thank you got putting the effort into writing it.

Why do grid points move with a change of coordinate system? My understanding is that projects are generally design on grid and then the scaling is handled by the chosen projection on site (normally inside the controller).

I feel it would be good if Trimble could highlight in TBC the different properties of each point as this could easily lead to a mistake on site. Today my set out points were 10mm different as a results of changing to a new site calibration.

Would you recommend importing design data as "Grid Only points"? 

Cheers

Sam

Great questions

This is one area where the need to support Survey Workflows and Construction Workflows in a combined product creates some issues

For construction I always use Grid Only Points that will always work best and means that nothing will change on you.

The create Point command currently however does not have a Create Grid Only Points option so if you have a lot of points to create - enter them into Excel and then import a CSV and you can set them to Grid Only Points during that import process

Alan

Sent from my iPhone

Alan: Thanks for the effort you put in to do this. Reading through it I had a couple of "so that's what was going on" moments. Of course, back at the time it was more like, "what the ---- is going on!?"

Thanks again, really helpful.

Marshall

For sure - I always feel that once I know how a product thinks it helps me to work with its tools - I always hate it when it does something surprising and I find the more I know about the engine, the easier I can drive the car

Alan

Sent from my iPhone

Alan,

This is a nice document that does indeed help explain to some degree how TBC is handling this info.  I would like to walk through a workflow that I think happens a lot in construction and see if I am getting this all correct.

We know that it is preferred by Trimble that you start you SCS900/Siteworks site in TBC through the Construction data tab and Job Sites.  After doing this we are typically either entering in data from a plan set or using a cad file to create what will become designs that we will later export to either data collectors or machines after a site cal has been completed.  This first step usually consist of getting your control points put together and from the document we should be importing them from a csv so that we can make them Grid Only points.  We are also quite possibly generating stakeout points that if we are picking them from a cad file should be doing so using the Create from Cad Command or else finding some way to get them into a csv so that we can import them as Grid Only points.  Again the key there is Grid Only Points I believe.  Am I correct so far?  At this point we create a design that we want to use and I like to create a site cal work order as well and complete only the site cal in that work order so as to keep that data all to its self in case you have to edit it at a later date.  I might also create a design and work order for staking some early construction features out such and limits, silt fence or even some structures or pipe.  That way after I complete my site cal I can possibly do some staking as well.  Now that I have completed the site cal and possibly some staking or topo I am going to either sync to my PC using a cable or TCC so that my TBC project can get the calibration information.  Once the sync is complete you will get a conflict in your TBC file saying your site information has changed and you will need to resolve the conflict by accepting the calibration.  Again am I correct so far?  Once you have done that I go into my project settings and computations and protect my site cal, control and designs.  That way I don't accidentally do something that would make it think it needs to kick out a new calibration file to the data collector.  Also at this point you may want to add additional controllers to the site so that they can receive the calibration and control point information as well.  Quite possibly you would be updating the office control point file to include the base station point that was created after you completed your site cal if you were using a unknown position when you started your base up so that the other controllers would have that point as well.  Am I going through this correctly so far?  I have personally had problems where I used grid points and had problems with things shifting as you know lol.  But I think it seems to be very key that we use Grid Only points for any points given to us from the engineer or surveyor keyed in from a plan set so that they don't shift and move.  I am exited to see that we get the option to set the type of point we are creating in the create points command.  However, there remain the issue of what happens if a person slips up and there project or points wants to shift.  Maybe a time stamp got messed up in the TCC to TBC sync and TBC thinks there is a different calibration file it needs to export but you want to just use the one off the data collector and you tell it to do so and you see a shift.  How do you get back to good?  I know we could simple delete the calibration and create a new one in TBC using our grid points and GNSS points from the original calibration but how does that affect your base point coordinate that was created after you finished your calibration the first time if you set your base on a unknown position and it saved the new control point to your field control file?  I am guessing that the coordinate of that base point point needs to be recomputed but I am not for sure how.  Another place where that comes into play is when you modify your calibration in TBC by turning on or off horizontal or vertical use of a point.  I would assume the base point needs to be modified as well.  I think there needs to be a more clear explanation of what the conflicts are and what it is wanting to do to fix them in TBC.  It can get a little confusing.  Like I have said I have brought in a calibration the first time and everything was fine until something weird would happen to a .cal or .dc file such as a time stamp and I tell it just use the controller file and my site shifts.  Its really frustrating because in my mind TBC is already using the one from the controller already unless it tweaks it a little.  And when you look at the details option tab inside the conflict tab it shows the database(TBC) is missing information that the data collector has, the horizontal and vertical calibration information as shown below.

To me there seems to be a discrepancy between TBC and SCS900 and how there are reading these calibration files, but I could be wrong.  My goal in all of this is to have a robust TBC and TCC workflow that I can count on and manage different controllers easily and machines as well.

Thank You,

Ben

Sam

Grid Points Move because they are recomputed each time there is a coordinate system change. Land Surveyors use this a lot - for example in Trimble Access, when you measure a Site Calibration for a project, as a Surveyor you may also pick up Topo while you are doing the site calibration measurements. So when you measure say 100 Topo shots prior to completing the Site Cal, when you complete and lock down the Site Cal it is different to when you actually measured the Topo, so the Grid Survey Points are recomputed on the fly using the current state of the site calibration - and it can change continuously when "Surveying". If at a later stage the Surveyor decides to "Extend a Site Cal" into a new phase of a project, they can do so in the same file as the original data was captured, and all Points and Stakeout Points (defined ass Grid Points" would be updated with the new Site Cal information. 

On the construction side we limit this in SCS900 / Siteworks so that the Site Cal has to be done and locked in prior to doing any Staking, Measuring or Machine Control. We also don't make it easy for you ass Users to change the Site Cal after it is locked in, for this exact reason - that we cannot be recomputing measurements and stakeout points all the time, otherwise you put them in the ground one day and the next day they are different. 

So once a Coordinate System / Site Calibrarion is locked in, the points should not move unless the Coordinate system physically changes - i.e. if you change a Coordinate System from Colorado North to Colorado Central - then all of the Grid Points for a Project will get recomputed into the new coordinate system.  If you go out and do a second site calibration for the same project, there will likely be differences (all be it small differences) between the first and second site calibration. If you import the second site cal into the project, it will overwrite the first one, and will force all Grid Data to be recomputed to the new coordinate system.

If you look inside a DC file, you will see that a Site Calibration contains a Rotation and an X, Y and Z axis shift as a minimum. If those values differ from one site calibration to another and you use them on the same project data you will get a different set of coordinates for the Grid Points.

Grid Only Points will not move, nor will your CAD Linework or Linestrings (unless the linestring is connected to a series of Grid Points in which case it will move). Surfaces will only change if they contain Grid Points.

If you see data moving that is not a good sign, it is being caused by a change in coordinate system and you need to identify why that is happening and what caused it to happen.

When all things are stable you should never see that occurring.on a construction project.

Alan