Coordinate System and Scale Factor

[shajahmadi]

When I change the coordinate system, it doesn't affect the scale factor, which it should. 

When I want to work on a drawing for a long road and implement it by GPS, I need it to be on the same coordinate system as my GPS. 

[Pointdump]

Hi @45eptop,
Design your corridor in either Grid or Ground, but stick to one or the other. If laying out with GPS, design everything in Grid. If you're laying out with a total station, design everything in Ground.
Dave

[45eptop]

thank you for the quick response.

I didn't design the corridor, my only job is to stake it.

[cyberflow]

Hi @Pointdump  do you know if there's a video of that presentation in 2010 at AU for the powerpoint ?

[ChicagoLooper]

@cyberflow 

2010?!

Don't know about 2010 but in 2019 Ken Martinez presented a class for a custom ground coordinate system in Civil 3D software and AutoCAD Map 3D software. You can  download class material and watch a video of that session >>HERE<<.

[Pointdump]

Hi Frank,
No, I've looked, and if Sinc made a video at AU it's lost.
Dave

[faniadv]

Did you find a solution/ answer to your question I have the same problem.

[Pointdump]

Hi Fanny,
More details please. Posting a drawing or screen shots of the problem would help.
Dave

[Cadguru42]

Before you import any points or start drawing anything you should always set the coordinate system and units to match what you need. If you're using a survey database then you need to make sure the database is setup to also use the same coordinate system and unit before importing any points. 

Changing the C3D drawing coordinate system does not reproject everything in the drawing. If you've already got drawing objects then there are two things you'll need to check in order to get them to proper coordinates. What's the source coordinate system and source units used? Pay attention to make sure the ACAD UNIT is set to match the C3D drawing coordinate system unit because it's not on by default (stupid Autodesk move).

You can use the Transformation tab in the C3D drawing settings dialog.

I haven't had to use this in over a decade, so I'm not sure if it works on both C3D objects and ACAD objects or only C3D objects. The help doesn't say (typical Autodesk), so maybe others with experience can chime in.

EDIT: This new forum format is ridiculous. I saw this and didn't even see the replies until after I wrote mine. I also didn't realize this was an older thread until I had posted the reply. Autodesk has really screwed up everything with the deleting of older posts and now this format change that makes it more difficult to navigate/understand what's going on compared to the older format.

[faniadv]

Hi, Everything is set up the way it should be, coordinate system and all.
The problem that I have is that the Scale Combined Factor shown when using
Prismodial (in the transformation tab) is not the correct one. I checked
against the Scale Combined Factor found in the NC Geodetic database, not
the same.

When using the option User Define (also in the transformation tab) and
entering the Scale Combined Factor found in NC Geodetic, the scaling of the
cogo points are not the right one.
I know they are not right because I am checking with the ones I scaled in
Carlson. Carlson gives me the right Scale Combined Factor . While I'm
trying to accomplish is to do everything in civil.
Thanks!

[Pointdump]

Fanny,
Please post a drawing with a few of those problem COGO Points.
Dave

[faniadv]

Dave,

Thanks for taking the time to look into this, the first one is the Combined Scale Factor given by Carlson, my PLS has check it and that is the correct number 1.00010405836813 .

The other 2 shots are taken from Civil as you can see the Geodetic Calculator shows a scale factor that does not match with the one above. The third shot is form the transformation tab, also shows a wrong combined scale factor.

Thanks

[Pointdump]

Hi Fanny,
(Grid)Scale Factor, as shown in your 2nd pic is calculated independently at each point. And to get the Combined Scale Factor you multiply the Grid Scale Factor by the Elevation Factor. >>>Elevation Factor=R/R+h<<<
Prismoidal Formula, according to the Help, >>>accounts for the fact that every point has a different scale factor.<<< But I have to say I don't know how it works in the Transfomation Tab. Which 2 points is it picking for that computation?
You can use >>>NCAT<<< to independently check Combined Scale Factor. You'll need Ellipsoid Height, not Orthometric.
If your PLS says the Combined Scale Factor is 1.00010405836813, then I would use that by selecting "User Defined" in the Transformation Tab.
Instead of the Transformation Tab, I think a better way is to create a custom affine projection. Read >>>Here<<<. If that sounds like something you'd like to try, please post a drawing in "grid" and at least 3 tie points at the extents of your area of interest.
Dave

[faniadv]

What I'm trying to accomplish is to calculate the scale factor in Civil 3D. Currently, I use Carlson Software to perform this task. In Carlson I go directly to a menu that scale points where it previously calculate the scale factor, that's how I convert my points from grid to ground.

My PLS showed me how to calculate the scale factor in Carlson, but I’m trying to figure out if there’s a way to do it directly in Civil 3D. Right now, I bring my points into Carlson, find the CSF, scale the points, export them to a point file, and then import the scaled points into Civil 3D, a lot of steps as you can see.

I just can’t believe that such a robust software like Civil 3D doesn’t have the same capability as Carlson.

[rl_jackson]

I reviewed you first post and went to your local area and the prismoidal factor that C3D provided for your points is indeed correct. What C3D does is assume you what to scale GRID data to GROUND, which in most cases this is true. It takes the Local Sea level elevation you determine and uses this to compute the CSF based on the prismoidal grid scale factor (notice in that box it says Grid Scale Factor) to determine the CSF. So no there's no direct way to determine CSF, in C3D, you're relaying on the data i.e. the Elevation Factor formula x Grid Scale Factor to be correct within the software.

As a rule, I use the Survey Database and import the data into the SDB. This then gives me the information in GRID and then I can import this data into a drawing set up my scale factor/elevation average and scale point on the Tranformation Tab. I then remove those points from the drawing. C3D does not scale on the fly like Carlson and MicroStation do, nor is there any sort of report of what it did short of when you reimport the points from the survey database (or just reimport the data), there will be two columns your local NE and grid NE. The key here is this, C3D does not scale automatically you must set up the scaling on the transform tab, then remove and re-import the points for the data to be scaled based on the information from the transform tab.

Note: If you want to go from Ground to Grid in C3D you need the Inverse of the Grid Scale Factor (1/x)

HTH