[HELP] Align and Scale COGO points without scaling Z values / elevations

[jstewartgeomatic]

Hello,

I'm trying to Align and Scale a set of COGO points to another set of points without changing the elevations.
Is there a way to do this?

Context:
We have a problem with a site localization/calibration for a GPS topo survey. We need to rotate and scale our latest points to our control points without changing the elevation values.

I've drawn a common baseline in each set of points, flattened both line(s), then I used the Align command and selected Y to scale to the flattened endpoints of each line. However, the Z values / elevations keep scaling up, too. The Z values don't change when just Aligning, however, when I try to use the Scale command (either as part of my Align command or separately after Aligning the points w/o scaling) the elevations keep scaling.

If I can't get this to work, I'm considering scaling the points, exporting a CSV file, then copy/pasting the correct/original elevations into the CSV of scaled X/Y coordinates. But this seems like a bit of a workaround for something that should reasonably be achievable in Civil 3D.

Thanks!

[Pointdump · Accepted solution]

Hi Jake,
"the Z values / elevations keep scaling up"
Yup, Civil 3D has always done that. Your Excel workaround is about as easy as any way. The Transformation Tab will do Rotating/Scaling without changing the Z's. So will a custom Affine Coordinate System.
"...this seems like a bit of a workaround for something that should reasonably be achievable in Civil 3D."
I agree. Head on over to the >>>Civil 3D IdeaStation<<< and post it up.
Dave

[Todd_Rogers]

@Pointdump can't you import them in from a survey database and translate it without affecting the Z elevation?

[jstewartgeomatic]

Thank you very much for your reply, I will definitely post in IdeaStation.

Seems like a relatively simple feature would be a second prompt in the Scale command to select between 2D or 3D scaling. 2D = scales X/Y coords only. 3D = scales Z as well.

[AllenJessup]

Import the points as 2D. Do your rotation and scaling. If you need the points at elevation. Export to a new Point File (CSV or whatever) and import them as 3D, overwriting the current points.

You can do that by either editing one Point Style or creating a second.

[jstewartgeomatic]

Thanks for your reply!

Yes, I ended up doing something similar to this method to fix my problem.
I Aligned+Scaled the new points to the old points in a fresh DWG (just to get the X/Y coordinates correctly scaled), exported as CSV, then copy/pasted the elevations from the original point file CSV into the spreadsheet for the new points (overwriting the scaled Z values with the correct original Z values). Worked like a charm.

I went ahead and posted a suggestion to IdeaStation for an option to select 3D or 2D scaling when scaling COGO points. I figure that this could be a useful feature that would streamline this process and make working with COGO points a bit more simple and flexible, but we'll see if the community and developers agree.

[Pointdump]

Hi Todd,
I honestly had never before used the Survey Database to Translate/Rotate points, so I looked at it just now. It will translate and rotate, but I don't think it will scale. I might be wrong on this. @rl_jackson would know.
Dave

[rl_jackson]

That is correct it will translate/rotate but not scale z values. You can however adjust the z value say from NGVD 29 to NAVD 88 or any other about but that's an across the board adjustment.

The only way to scale the data ie. Grid to Ground is through the Transforms Tab in the settings but setting a scale factor and a average elevation above sea level.

[Jeff_M · Accepted solution]

I'm a bit late to this post but the Sincpac-C3D add-on has had this capability for about 15 years now.

https://info.quuxsoft.com/SincpacC3D_Help/SP_ScalePoints.htm

[MikeEvansUK]

I've not used this survey aspect but in times of need (like this)..
I create a blockobject of the data, rotate / reposition and scale the geometry (AdeTransform) then change the Z scale back to 1.
That should affect the geometry scale x/y but not the Z axis.
Explode the block and the points should be in the new location but retain the original Z values.

Mike