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 it would never splice into a "just moved" map
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, we 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 “select coordinate System” button we choose the origin system.
3. In this example, I have a map in NAD27, so we choose this system in the “select coordinate system” button; I want to pass this to NAD83, I assign it to the next button on the same panel (source drawing). With the “select drawings” button, the file (or files) to be reprojected is chosen.
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 browser for the original file, once we have found it we apply the “add” button
7. With the drawing added, we are now going to set up a query. To do this we right-click on “current query” from the map browser panel, and select “define”.
8. From the Query panel results, click on “location”, under “query type”, and then click “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 “draw” option as the “query mode”.
9. After defining the query, we press the “execute query” button. Once AutoCAD Map 3D finishes the process, we do a zoom 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.
Vía: The CAD Geek Blog