I am ever so grateful to ya'll for your willingness to share your knowledge.
I am currently using Leica GPS1200 units with LGO software. Our surveyors HAVE to have the results in ground coordinates (they don't know how to spell "grid" and refuse to learn - attitude backed by management). So my problem.
When using Trimble TGO, I would select a point generally near the center of their project and convert the grid coords to ground coords using the scale factor at the point I had chosen. When our guys would gather more data, I would use the same point to convert the newly acquired data to ground - and all lived happily everafter because they were all in agreement.
With LGO, apparently, I do not have an option of selecting the point to use to generate the scale factor from. Therefore, when points are added and I raise them to ground, a different point (or I suspect a "new point" is created) and therefore the makings for divorce are created as now the first set of data and the second set of data are NOT in agreement and the two cannot get along.
Am I missing something here?
It seems like if I convert the coords to ground using the Leica LGO method, then any work Done prior to that in our cogo routine, would have to be translated/transformed to the coords generated from the second set.
Thanx for your help
Geezer:-P
I'm not very familiar with LGO, and I quit using TGO YEARS ago, but...
It sounds to me like you are doing a “local modification” of the State Plane Coordinates. This would be described as ANCHORING a single SPC Coordinate (holding the true SPC as FIXED), and scaling everything else (all other SPC values) “UP” based on the Combined Factor (CF) of the “anchor point.”
I know that TGO will do that (seen it), and it's my least favorite grid-ground modification technique. Be that as it may, it “works” (I suppose) if everybody is on the same page. However, NOT every software package supports that method, and without GOOD metadata, it's a real bear to reproduce.
The more common technique round these parts is to SCALE ALL of the SPC values by the CF (and hopefully truncate a couple numbers off the left side), this is what I call the Global modification method.
I personally despise BOTH of these methods, but that's just me. Given the choice, I would rather try and “reverse engineer” the latter than the former (much easier).
That said, I'm pretty sure that LGO does support the “global” Method, but I don't know about the “local” method. LGO DOES however support project specific LDPs very well (or so I'm told), as does TGO for sure.
Loyal
Set your modifier in the project properties "Coordinates" tab.
if you choose a state plane system as your basis for the project, then you can check the little box and apply an average combined factor plus a N,E translation value so the coordinates don't look like state plane.
Use Corpscon to derive a combined factor, or however you like to do it.
Geezer,
Simple task in LGO.
LGO | Project Properties |Coordinates > Create/Define/Attach Coordinate system to this project; Example:(AZ_Central_NAD83),click OK,
Open the LGO Project your working with, select the View/Edit tab,
Place a "Fence Around" on the points in the GNSS project,
All the Points and associated baselines will turn "BLUE",
Perform a Right-mouse click...
After Right-mouse click, pop up menu appears,
Select: Compute Avg Combined Factor...
From the "Compute Average Combined Factor" | General menu:
Average projection scale factor: 0.9999353243
Average elevation factor: 0.99990517743
Average combined factor: 0.9984050732
To generate modified ground coordinates:
check the tick box for:
Apply average combined factor to to obtain modified grid coordinates including shifts:
Northing shift: [ ]
Easting shift: [ ]
I WOULD HIGHLY RECOMMEND ENTERING SOME TYPE OF N/E SHIFT,
to generate modified ground coordinates to differential the physical numbers.
Something thats going to jump out to you, definately NOT SPC NAD83 coordinates.
Good luck,
-BbB
