IMPORTING DWG/DXF FILES
This exercise can cause a lot of frustration for users due to the very basic incompatibilities between AllyCAD and AutoCAD.
When the drawing is originally created in AutoCAD you have no option of specifying a particular coordinate format as AutoCAD supports only Cartesian style coordinates. In AllyCAD however you can specify the use of Cartesian coordinates, or of Surveyor coordinates in either the Northern or Southern hemisphere.
Cartesian coordinate systems have the 0 angle horizontally to the right with angles increasing in an anti-clockwise direction, horizontal coordinates increase to the right, and vertical coordinates increase in the upward direction.
Southern hemisphere coordinate systems on the other hand have the 0 angle vertically down with angles increasing in a clockwise direction, horizontal coordinates increase to the left, and vertical coordinates increase in the downward direction
As you can see, this system difference causes a lot of problems when importing drawings from AutoCAD. In order to import such a drawing correctly you will need to follow certain steps:
- Never use the File Open command to load a DWG or DXF drawing which is in survey coordinates. When you use this command a new CAD window is opened by default (you can change this feature using the Settings › System Settings command). This CAD window has a default coordinate system that is based on the settings made in your startup drawing (called STARTUP.DRG and stored in your User directory). If this default system is not set correctly, the imported drawing will not be displayed correctly.
- The correct sequence of events is to first use the File › New command to create a new CAD window.
- Then use the Settings › Drawing Settings command and set the drawing scale to 1:1 (1 mm to 1 mm) if the original drawing was in millimeters, or to 1:1000 (1 mm to 1 m) if the original drawing was in metres, and the Coordinate System to Cartesian.
- If you are using a version of AllyCAD prior to version 3.2G then you must click on the Angular Format button and specify the 0 point at 3 o’clock and measured anti-clockwise. AllyCAD versions from 3.2G onwards will automatically set the angle style when you change Coordinate System.
- Now use the File › Load › Load Drawing command to load the DWG or DXF file into this new window. In this way you will be using the correct drawing format settings, and the drawing will have the same coordinates as in AutoCAD.
- Once the DWG or DXF file has been imported your drawing should now display correctly. You can now change the drawing scale to what you require.
If the drawing is meant to be in Surveyor format then there are some additional steps to be taken. This will however require that you have a reference position on the drawing for which you know the survey coordinates. Without this reference position it is virtually impossible to position the drawing correctly.
- Once again use the Settings › Drawing Settings command and set the Coordinate System to Surveyor.
- As stated previously, if you are using a version of AllyCAD prior to version 3.2G you must click on the Angular Format button and specify the 0 point at 6 o’clock and measured clockwise. AllyCAD versions from 3.2G onwards will automatically set the angle style when you change Coordinate System.
- Now click on the Surveyor Setup button, set the coordinate order and hemisphere as required, and type in the coordinates of the known reference position. Make sure that the check box labeled ‘Set origin at known point’ is checked then click the OK button to close the Surveyor Settings dialog. Click the OK button to close the Drawing Settings dialog and you will be prompted to click on a point with the coordinates that you entered in the Surveyor Settings dialog. Locate the reference position on your drawing and jump to the point using the Jump snap (key J) for a point, or the Intersection snap (key 0) for a line intersection. Press the [Enter] key and your drawing will now have the correct coordinates in the chosen Surveyor system.
The import is now finished and the drawing is correctly displayed in the coordinate and drawing system you require. It will however most likely not be centred on your screen so use the Zoom All command (keys ZA) to see the full extent of the drawing, then use the Settings › Re-Center Paper command to center the paper on the drawing.
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