How to change a map from NAD27 to WGS84 (NAD83) with AutoCAD

Before we talked about why in our environment, most of the old cartography Is on NAD 27, While the international trend is the use of NAD83, or as many call it WGS84; Although both are actually in the same projection, the difference is only Datum (differ only in the UTM grid).

Many enter into a terrible confusion believing that the map only requires to be moved a vector, which in the case of Honduras in the cartographic leaves says that it is 202 meters to the north and 6 meters to the east; Of course this can be applied to local jobs, however when doing a reprojection as it should be, computer programs do a series of geodesic operations on the ellipsoid change resulting in a map where all the vertices have been moved in the grid a value Not constant, so that I would never connect with a map "simply moved"

It can be done with Microstation Geographcis, ARCGis or with Manifold; in this case we will see how to do it with AutoCAD Map3D. I will use what I have (Map3D) in English so we will try to keep some names as they are in the menus and buttons and as the friend CADGEEK has originally proposed. You should know that AutoCAD Land Desktop and AutoCAD Civil 3D, previously AutoCAD map ended up being this application that AutoCAD calls Map3D, the procedure has not changed for different versions.

We start by doing it with a blank map:

Assign projection to original map

1. We start a blank drawing

2. Using the "map classic" workspace, go to map / tools / assign global coordinate system. In this way our dwg already has a reference system, many here are wrong because they only assign the new system, which would cause erroneous data. In the button "select coordinate System" we choose the origin system.

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3. In this example, I have a map in NAD27, then we choose this system in the "select coordinate system" button; I want to pass it to NAD83, I assign it to the next button of the same panel (source drawing). With the "select drawings" button, choose the one (or the) files that you want to reproject.

4 Now that our map has a coordinate system, we open the task panel if it is not activated. It can be done with the MAPWSPACE command bar, then enter.

5. Now from the "map explorer", we right click on "drawings" and select "attach"

6. The dialog box that appears allows us to search the original file in the browser, once we have found it, we apply the "add" button

7. With the drawing added, now we are going to configure a query. To do this, right-click on "current query" from the map browser panel, and select "define".

8. From the results of the Query panel, click on "location", under "query type", and then "ok" to accept "all boundary type". This implies that if we are going to consult the original drawing in its entities, with the "query type" defined, we select the option "draw" as the "query mode".

9. After defining the query, press the "execute querry" button. Once AutoCAD Map 3D finishes the process, we zoom out extents and you can see the reprojected drawing.

It is worth mentioning that some Civil 3D objects do not like to move that easily, as it is the case of complex plots (several figures, a record) or those that are like islands (plots within plots); those that are topologically dirty such as those built with smartline and other aberrations. They are usually blocks or groupings that need to be exploited before reprojection.

Via: The CAD Geek Blog

15 Replies to "How to change a map from NAD27 to WGS84 (NAD83) with AutoCAD"

  1. Thanks, and testing to see if this is true

  2. Hello everyone I recently started working on the AutoCAD Map 3D (the one that comes in the AutoCAD Civil 3D Land Desktop Companion) and I need to work on orthophotos from my country (Guatemala) the matter is that I need to create my projection because I already have the necessary definitions to configure it, if someone knows how to do that or has an idea, I would greatly appreciate it, thank you very much ...

  3. Very good tutorial ... and the other way around? If I have information in WGS84 and I have local parameters to transform to a local datum.

    In the definition of coordinate systems only parameters can be entered from the local datum to WGS84. Is there any way to do it?

    Personally, I have calculated parameters under the Bursa-Wolf model, but I do not know if Autocad Map uses the same equations.

    Thank you very much.

  4. Thanks for your help g! I will perform some tests and let you know the results.

  5. With Microstation:

    First you must Assign projection To your dgn, selecting UTM zone 16 North, and the datum in which you have the information.

    Then you select the command that already Brings included Microstation, To send to kmz, he himself makes the conversion to geographical and selects the datum wgs84

    I warn you, this does not work for you only Microstation XM, occupies Bentley Map or Microstation Geographics

    With AutoCAD:

    Before battling with the Civil 3D fdo, you should take a look at an extension that is on the part of AutoDesk to export dwg models to kml

    http://labs.autodesk.com/utilities/google_earth_extension_beta/

  6. Hello I am a beginner in the subject I work with maps in XY coordinates or flat if I work in MicroStation MX or AutoCad Map3d as I convert them to latitude and longitude, to then create a KML file and visualize my file in Google Eart my UTM zone is 16 I am from El Salvador, thank you for your support.

  7. I need a programmer that generates the utm mesh automatically in an Autesk Map 3D file, the one I had is for an older version, it generates an error and exits the application

  8. I was referring to draw them automatically with autocad map 3d

  9. Hello Geobruu, in this post Explains how you can build it ... in some of the links of the post explains the concept to understand it.

    regards

  10. What I could not do is draw the lines representing the utm coordinate system

  11. I have used the ones that the program brings by default; The suggestion given by the local geographic institute is a vectorial displacement but in practice it is not very functional because as the latitudes approach the equator the displacement vector changes.
    What happens is that in the case of Honduras, the whole country falls within the same area (16) and only a small fraction in the 15 zone.
    At the end, when comparing both methods are differences smaller than ten centimeters in the south (as the latitudes advance towards the equator)

  12. Okay, now it's clear.

    In the specific case of your area, have you calculated your own transformation parameters, or do you use the ones provided by the corresponding Geographic Service or do you use the ones that the program brings by default?

    That is, are the results of the transformation precise, in what order, or only approximate (several meters)?

  13. Yes, I was a bit confused, I tried to clarify it.
    In the first graph, in the same panel, in the first option we choose the origin system and in the second the target system, then in the button to choose the drawing, we take the map that we want to reproject.

  14. What I do not understand or do not see is where you define the NAD27 startup system.

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