Coordinate Systems: Spectra Precision Ranger 3 and Civil 3D

You are using UTM, it's a world wide system and the distance you are east or west from the central meridian of the zone will determine how much of a rotation you will have from true north. UTM zones are large and this one's central meridian is W111degrees. Picking a projection with a central meridian closer to your site will minimize the rotation from north. Also, there will be a grid scale and elevation scale factor that will probably shrink your distances.?ÿ

I'm hoping that someone with more local knowledge will chime in. But I think that your problem, as you suspect, is in the projection system you have set. Or maybe in the one you are trying to match. That is, not really a "problem" with either, but a mis-match.

These "coordinate systems" are not datums. They are projections of the datum to a coordinate system. You can take a unique lat/long position and project it to quite different coordinates depending on the projection you apply.?ÿ

UTM zones are 6 degrees of longitude wide. As such the results have rather large "convergence angles", probably 2?ø - 3?ø would be in play. I've done some googling of the Alberta Survey Control Network and it seems that coordinates may be reported?ÿ in UTM or another zone known as the "3TM" zone, which are half as wide and therefore would have?ÿ much smaller convergence angles. Mixing data from these 2 would result in the rotational error you are seeing.?ÿ

Also possible that the UTM 12 Zone is not the appropriate one to be using for your project area. UTM 11 would be more appropriate in Western Alberta.?ÿ

I also add that UTM is generally inappropriate for use in urban environments. Because the zones are very large, the scale factors and convergence angles get very large. So UTM is not commonly used for boundary surveying.?ÿ

@mightymoe Thanks for the reply and explanation.

I know this is Canadian based, but I'll ask.?ÿ Based on what coordinate system is shown on the Ranger, is Civil 3D using the right matching coordinate system?

I've attached an image of the transformation tab in the Civil 3D settings.?ÿ Since the coordinate system on the Units and Zone tab and the transformation tab are the same, would transformation settings have to be applied (with the checkbox "apply transformation settings")??ÿ Or is the grid scale and elevation scale factor you mention something else entirely??ÿ Thanks.

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Run, don't walk. Leave as fast as you can. You should be applauded for trying to figure out how to make all of this work. On the other hand the company who has put you in this position is not one you want to be involved with. You are using professional equipment to I assume produce a professional product without the required training or knowledge.?ÿ?ÿ You do not want to waste your developing career taking direction from the management responsible for this.

@briancanada?ÿ

I don't like the numbers in the Reference Point box. I went through a short UTM phase in the early 1980's and quickly stopped using it cause of the huge convergence and distance adjustments. So I'm not any expert dealing with C3D and UTM.

The easy way to tell if you have C3D set up correctly is hover over a point and it will list the XYZ and the LAT LONG for that point, it also should show the convergence and scale factor at the points location. Those numbers should match what you have in your GPS data file for the same point. If geographical data is important to you to have in C3D then you want it to match the GPS file. But you need to understand that C3D is basically creating an XYZ file that will be the same no matter the projection. What won't work is the placement on the globe if your set-up is messed up. Does anyone even care for this lot survey?

Posted by: @mightymoe

Those numbers should match what you have in your GPS data file for the same point.

You can also figure out about what a reasonable lat/long of a point should be using Google Earth, or a cell phone. If things aren't set up right in C3d you won't be anywhere close.?ÿ

@norman-oklahoma @mightymoe @ lurker

Good Day,

Based on the replies it seems that the rotation/skewness of the survey points is due to the selection of the coordinate system and the meridian it references.?ÿ More for informational purposes, I've uploaded a couple of images showing the coordinate system in Alberta.?ÿ And as I mentioned we are not a survey firm, but an engineering firm where we use the Ranger to survey for site plans for reports, such as borehole drilling locations, excavation locations, site features, etc.?ÿ So nothing fancy nor anything considered even close to legal.?ÿ If we need something legal, we hire a registered survey firm.?ÿ Before we got the Ranger we used a Leica TPS800 for surveying sites.?ÿ I went down this rabbit hole when I noticed my site plan being slightly rotated instead of horizontal like it looked like in Google Earth or how the site looked on the registered survey plan I uploaded.

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I thank everyone for there replies and assistance, it is appreciated.

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Whatever that blue zone is you may want to use it to aid in tilting the project closer to north. Understand however, there is a trade off with Transverse Mercator zones. You will be close to the Central Meridian so your direction will have a small convergence angle. But, the grid scale factor will be as large as it gets in the projection. In other words the surface of the projection will be a good distance below the earth's surface and that will shrink your distances. How much depends on the scale factor at the central meridian and the elevation the site is above the earth. At the edges of the zones your distances will be closer to the surface so a smaller shrink, but your directions will be skewed more.?ÿ

@mightymoe Thank you for the explanation, it is appreciated.

I don't know what the transformation is precisely, but I got wondering that if you specify UTM 12 (Canada) in the Spectra software you may try matching it to the NAD83(CSRS) coordinate system available in C3D (CSRS.UTM-12N) - the Canadian Spatial Reference System - instead of the universal version.?ÿ Not sure why they would be different.

A better route might be switching both to the "universal" system, idk

I noticed an autodesk thread about the shift that may (not) help either; it regards some transformation in AutoCAD Map, which is built on top of C3D:

https://forums.autodesk.com/t5/autocad-map-3d-forum/csrs-datum-shift-and-bing-live-maps/m-p/9422903#M56755

If you wanted to do some specific research, it looks like you can run some test numbers at the nrCan site:

https://webapp.geod.nrcan.gc.ca/geod/data-donnees/transformations.php

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Punching Terrace Heights Alberta CA into Google Earth returns longitude 113 26 09, which is in UTM Zone 12, but just barely. Zone 12 covers from 114W to 108W, so you're half a degree away from the edge of Zone 12.

That means that you're near the maximum difference between UTM grid north and geodetic north, so a big difference between grid and ground azimuths is guaranteed.

As to why the two black boxes disagree, a crusty Nam vet network tech who kept our little partly bootlegged network up and running in the late 90s, accused me many times of having a "user head gap." In today's world of SSDs, that's losing its meaning, but ol' Roger was right more often than not, about me at least.

You just have to dig deep to find the problem.

@mathteacher?ÿ

Is a user head gap anything like PEBKAC ??ÿ (Problem Exists Between Keyboard And Chair, a favorite for the Geek Squad.)

@bill93?ÿ

Very similar, I think. Those tech guys have many coded insults to hurl at clients who are too quick to pick up the telephone. Roger taught me better.

@bill93?ÿ

Like the

ID10T error??ÿ

@dave-o?ÿ Thank you for the suggestions on the coordinate systems and the links.?ÿ I'll check them out next week.

@mathteacher Thank you for the explanation regarding latitude and longitude and the zones.

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@jitterboogie?ÿ

Or the PEBKAC principle.

Hi Brian

A few concerns. What are you using the Survey Pickup for (design, Asbuilt record?) and will you be sharing anything out to Clients or Contractors??ÿ Just based on your admitted experience, im concerned that figuring out matching coordinate systems within C3D and your Survey software may not be the best use of your energy.?ÿ Can you share some more details of your site??ÿ Mainly, is there previously established Site Control??ÿ Are you going to be doing any layout? Where you supplied a Legal Base? Anything in Edmonton should be done in 3TM, i notice your set to HT_2.0 and most of Alberta is using GSD95, and Can-net defaults to CGVD2013.?ÿ for your experience level i would also not set a coordinate system in your C3D, your not familiar enough with what your data collector is spitting out adding another variable (CAD coord sys) wont help.?ÿ?ÿ

Sorry lots of questions, but send me a message if your still need help (i believe your post is 3 days old)

@jimmac

Hi Jim, thanks for the reply.?ÿ The survey data is used to generate site plans for our reports.?ÿ The figures show some general site features and the work we undertake on a site.?ÿ This could included the location of boreholes, retaining walls, remedial excavations, topos, cross sections as needed based on excavations.?ÿ We also use lidar data for slope analysis.?ÿ Pretty general, and sometimes basic, figures that deal with geotechnical or environmental work.?ÿ The first image I uploaded in my first post is an example.?ÿ

I noticed in your profile you're from Alberta, so you know that site controls in the Edmonton area include property pins and Alberta Survey Control Markers.?ÿ That being said when we survey we do not make an effort to go and find or survey either of them unless they can be easily seen or required for the project.?ÿ We tend to survey, download the survey data, import into Civil 3D, align the survey data over an aerial, and then generate figures for the report.?ÿ We do not usually undertake any layout, unless for example, to layout planned borehole locations in an area.?ÿ We do not do legal surveys.?ÿ We are very seldom provided a legal-base.?ÿ Sometimes we do receive dwg files from clients, but they usually have their coordinate system specified for the file.?ÿ And, I cannot remember the last time we shared a dwg file.?ÿ We previously used a Leica TPS 800 for surveying, but our owner upgraded to the Spectra a few years ago to improve our accuracy, allow one person to survey, easier topos, and allow easier surveys in more remote areas, such a undeveloped areas where it would be difficult to use the TPS 800.

The settings in the Spectra, as shown in the previous screenshot, were how we received it, so to speak.?ÿ That is, when we use the Word wide/UTM the other settings self populate and we do not change them.?ÿ After I went down this rabbit hole of trying to understand why our survey was skewed and based on some replies I had a look at the Spectra settings and tried to find a 3TM coordinate system to use but their descriptions are a bit difficult to understand.?ÿ I have a support call into Cansel to see if they can provide some guidance for selecting a 3TM coordiante system in the Spectra.?ÿ And yes, we did have some limited training on using the Spectra, but it was more this is how you turn it on, how to connect to Cannet or a base station, how to download, etc.?ÿ Nothing really on selecting coordinate systems.?ÿ Each of us in the office use to do our own drafting in C3D or LT for our projects, but for the few months we've had a draftsperson to complete the drawings.?ÿ They are fine with working with coordinate systems in C3D but are not familiar with Spectra settings.

Based on your reply, you recommend that when bringing the survey data into C3D we set up the dwg file as having no coordinate system??ÿ I'll mention it to our draftsperson to try when they are back from a few days off.

Appreciate all of the help.

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