topic Local Northing _ Easting Vs Grid Northing _ Easting. in Civil 3D Forum

Local Northing _ Easting Vs Grid Northing _ Easting.

Muthya — Sun, 24 Sep 2023 05:19:31 GMT

I have received a Civil 3D Model and having some doubts.

This is the opening screen:

I know the location. So, I apply the appropriate values. Here is what happens:

There is a local translation applied to the UTM Zone 40 WGS84 Coordinate system due to historical reasons. So I open this tab and click on "Apply Transform Settings". Pick a reference Point from the drawing. This is the screen:

Here are the real-world values are attached as a xls file (Tie in....xls).

I have provided these values:

Just checking if I am correct.

Thanks.

Re: Local Northing _ Easting Vs Grid Northing _ Easting.

Pointdump — Sun, 24 Sep 2023 15:45:48 GMT

Hi Seshagiri,
Thanks for posting your Tie Points.
The default numbers that come up under Reference Point are the center of the Useful Range of the Projection.
You'll choose a point in the center of your project as your Reference Point. Maybe point #654. The Transformation Tab treats this as a scale, not a translation, so the farther you are from your reference point, the more the scaling distorts your coordinates.
Dave

Re: Local Northing _ Easting Vs Grid Northing _ Easting.

Muthya — Mon, 25 Sep 2023 03:16:14 GMT

Thanks for your response.

So, what is my choice if my intention is to "Translate" not scale at all.

Thanks again.

Re: Local Northing _ Easting Vs Grid Northing _ Easting.

Joe-Bouza — Mon, 25 Sep 2023 04:21:15 GMT

Hi Dave

i never bothered to explore that transformation tab before. Is that similar to LDDT base point north rotation?

specifically, once in a while I’ll get a local survey with rotation and line labels are useless.

Re: Local Northing _ Easting Vs Grid Northing _ Easting.

Pointdump — Mon, 25 Sep 2023 09:45:27 GMT

Seshagiri,
Looking again at your spreadsheet, it looks more like an increase by scale instead of translation:
Point #1
E Delta: 0.18 N Delta: 0.137
Point #749
E Delta: 0.207 N Delta: 0.178
I spent quite a bit of time trying to discover a combination of Reference Point and Scale that would work, but I was unsuccessful.
So we need to take this to a whole new level. I created a custom projection by duplicating and then altering the UTM84-40N projection. Use MAPCSLIBRARY to see the parameters of the custom UTM84-40N_Affine projection. (When you open my drawing it will ask you if you want to add the custom projection to your library.) Importing UTM84-40N points you'll use the "PENZD_UTM-40N" Point File Format.
Drawing and spreadsheet attached.
Dave

Re: Local Northing _ Easting Vs Grid Northing _ Easting.

Pointdump — Mon, 25 Sep 2023 10:01:47 GMT

Hi Joe,
I didn't use Land Desktop. I jumped pretty much straight from Softdesk 8 to Civil 3D 2010. And since I was just laying out building grids, I created my own drawings and didn't care where north was. I was handed control points referencing building grids.
I didn't even know what the Transformation Tab was, heck, even what a coordinate system was, until Sinc piqued my interest. The Transformation Tab has a glaring defect: Map commands don't work. So you can't bring in shapefiles and it breaks Bing imagery.
Dave

Re: Local Northing _ Easting Vs Grid Northing _ Easting.

Muthya — Mon, 25 Sep 2023 10:21:21 GMT

Thanks so much for spending substantial time on the subject and trying to educate me.

This needs some explanation now.

It all originates from surveying work and some design data.

I am supplied a set of Bench Marks and Coordinates. It states that this is in xxxWGS84UTMzone 40Metric system.

When I observe these points using GPS with the WGS84 UTM Zone 40 selected, the observed values differ from the values supplied.

My standard Survey workflow in such situations is to "Observe" with GPS the given points, usually about seven or eight (may be more) of them which form an approximate outer boundary and include a couple some where in the middle of the area. The software within the GPS device allows me to perform a "Localization". This essentially involves Seven Parameters. (Three Translations, Three Rotations and a scale factor). This works excellently. We have had no issues any time before.

In the present case, it looks like the designer of the infrastructure project has used one of the two systems (WGS84UTMzone 40Metric Or xxxWGS84UTMzone 40Metric). However he has not defined them in his drawing settings. So, I am trying to figure out.

For the limited extent I am working on, I thought of using an "Average Translation". May be there is a small Rotation Element also involved in the 2D environment (On Z-Axis) which I thought I will ignore.

Adding to the confusion is that I have also been supplied 3D BIM Models with similar constraints !!!

Trying to figure out a solution.

I am surprised Civil 3D is not providing a simple "Translation" parameter in the Transformation tab of the Drawing Settings.

If you find any possible solution to this vexing issue, please educate me.

Thanks.

Re: Local Northing _ Easting Vs Grid Northing _ Easting.

_Hathaway — Mon, 25 Sep 2023 20:22:19 GMT

I think you are creating a ton of extra work for yourself. The surveyor has the scale factor information you are missing. They may of said is its state plane XXXX system. But it sounds like it on that system but scaled to ground. This is practically a requirement for all work we do. I guarantee you the surveyor has this information.

They probably just didn't setup their cad files with all the correct system information (it really is quite surprising how many firms still do this). Or, it may of been exported from another software and not carried the correct state plane settings over.

Re: Local Northing _ Easting Vs Grid Northing _ Easting.

Pointdump — Tue, 26 Sep 2023 07:18:38 GMT

Seshagiri,
"I am surprised Civil 3D is not providing a simple "Translation" parameter in the Transformation tab of the Drawing Settings."
I've been chewing on this. Maybe a "User-Defined" Scale Factor of 1 will do this.
Dave

EDIT: I tried this just now and it works to provide a simple translation of all points.

Re: Local Northing _ Easting Vs Grid Northing _ Easting.

Muthya — Tue, 26 Sep 2023 07:20:14 GMT

It has to be "TRANSLATION". There already is a "Rotation" element available.

If we had a "User Defined Coordinate System" within, maybe it would have helped.

In the particular case I am describing I do not have to scale.

Also, the translation is very small (some 0.18m and 0.14m in Easting / Northing).

Thank you very much.