AutoCAD is the most widely used design program, standard equipment in every technical office that manages architectural, surveying, engineering and designing issues. Its large spread in the technical world has prompted many engineers to use it in applications that are clearly in the field of Geographic Information Systems (GIS). Soon, AutoDesk, AutoCAD parent company, gave the market a more suitable module, AutoCAD Map, which, without being a real GIS, combines the flexibility of a design application with the structure of a GIS. However, the vast majority of AutoCAD users still remain to the design version. Thus, the majority of the communication between engineers even in matters purely cartographic as planning, topography and surveying, is based on AutoCAD files. This choice presents two main drawbacks:
1. The AutoCAD environment does not endorse any particular coordinate system. It is essentially an environment with arbitrary coordinates, based on the (0,0) of an independent Cartesian space, where the user can place a plan (with dimensions from 0,0 up to 100,100 in meters) or a map with plannar coordinates (with dimensions from 450000,4300000 up to 550000,4500000).
2. AutoCAD does not follow the known protocols and conventions of GIS world, but puts his own, apparently suitable for design applications. However this option complicates the data transfer from one platform to another. Thus, a georeferenced map image in ArcGIS (which is the most suitable software program for creating georeferenced images) cannot be directly introduced in AutoCAD. The user has to find an add-on written in LISP to “convert” the georeference file of the image and create the 3 (literally) values needed in AutoCAD to place the image. The same goes for the vector data, with innumerable problems in converting a plan (DWG) to the standard cartographic data protocol shapefile of ESRI and vice versa,problems usually circumvented by the intermediate conversion to DXF (AutoCAD Exchange Format), but almost always with information loss. These problems become much more pronounced because AutoDesk changes the DWG protocols in each version, creating an entire list of conversion options (for AutoCAD 12, for AutoCAD 13, AutoCAD 2007, AutoCAD 2009, etc.). Fortunately, the simplistic DXF, with the simple text file structure, remains more or less constant.
The above limitations of AutoCAD can be overcome and eventually it is possible to introduce purely cartographic data and compose a complete map (with much less flexibility of GIS). Many applications and add-ons intent to facilitate this task, and in the scope of this topic, the question is how to exploit the TopoNavigator’s ready maps in AutoCAD environment, how to transfer data from the GPS through TopoNavigator into AutoCAD and to a lesser extent, how to transfer AutoCAD files in the TopoNavigator environment.
1. Export cartographic images and imported in AutoCAD.
Since version 542, TopoNavigator5 during the georeferencing or the export of a georeferenced cartographic image creates an adjacent text file with an explicit name (starts with the image file name and ends with the prefix _CAD, eg Map1_CAD.txt), that it can be opened with any text editor. The file has contents like the following example.
In the form that appears deselect the parameters “Specify on screen” and enter the values in the textboxes that are enabled.
In the first section put the x and y of the lower left corner, that you had copied from the series STEP1 (“Left-Bottom corner x & y”).
Then in the second section introduce the values of the series STEP2 (“Scale”). The comment in the series STEP2 refers to the AutoCAD paradox to call the image width (in meters) “Scale” (ie. “scale”).
With these three values (x, y & Scale), the image is transferred to its true position. The last two values of STEP3 (“Verify Right-Top corner x & y”) help to confirm the proper placement of the image, by putting the mouse in the upper left corner.
The third section acknowledges the shift of the image, which in the case of images extracted from TopoNavigator5 is equal to zero.
If your workspace is a new blank project, you will need to press Zoom to Extents ,
primarily because the window has opened in the region of 0, 0 of the arbitrary coordinate system. If you have data and you are in the picture’s area, you will see it immediately be placed under the vector data.
If you already have georeferenced maps or georeferenced satellite images, you will see slight variations due to changes introduced by the georeference of these images. In this case, you can move slightly the new or the old image to adjust them on the vector data or on accurate Ground Control Points.
Open the TVP file from TopoNavigator5 file manager and by right-clicking the file select “Save As”. Select the protocol DXF and save the file. Then just open the file in AutoCAD.
In case you want to import the file into an existing AutoCAD project, then a simple way is with the menu Insert / Block.
In the form that appears deselect all “Specify on screen” parameters and click OK.
The AutoCAD project has to be in EGSA87. If the project is complex and contains many layers and the elements you want to export are scattered in different layers, it is preferable to choose the data you want to export, copy and paste them into a new, empty project. Then export the new project in a DXF protocol. In TopoNavigator5, if you want to just view the data (not edit them), import the DXF file in TopoNavigator5 from the menu Map/Add Level. If, instead, you want to edit the data, you will have to convert them it into the editable TVP protocol, adding it with the Add File button in the File Manager and saving it as a TVP file.