Lesson26- Introduction To POLYLINES



PLINE PL (alias)

D r a w + Polyline

Draw

One way to create a LWPOLYLINE is to use the Pline command.

  • Pline (an abbreviation for PolyLINE) is used to create single objects that can be made up of multiple LINE & ARC segments.
  • as an example, the shape below could be made from 9 individual LINEs & one ARC or it could be made from one LWPOLYLINE.

Prior to AutoCAD Release 14 the Pline command created POLYLINE objects but now these objects are Light Weight (LW)

  • LW signifies that the method for storing polyline data requires less space (to be managed more efficiently by AutoCAD).

Why Create LWPOLYLINEs?

LWPOLYLINEs can require more effort to create & edit compared to using Line or Arc commands to make individual LINEs & ARCs.

  • if you do not require the special properties of LWPOLYLINEs then you should probably use individual LINEs or ARCs instead.

LWPOLYLINEs offer the following benefits

  • you can select an entire shape by selecting only one segment 
(which makes it easier to Copy, Move, etc…)
  • you can use Region to convert LWPOLYLINEs into REGION 
objects to perform an analysis (area, perimeter, centroid, etc.)
  • each LWPOLYLINE segment can have a different Width (the 
width of other 2D objects is controlled with Lineweight instead).
  • you can perform 3D operations on LWPOLYLINEs which makes 
them very important objects if you plan to work in 3D.

Another way to create a LWPOLYLINE is to create the desired shape with individual LINEs or ARCs using Line & Arc

  • and then use the Pedit command to Convert and then Join the individual segments into a single LWPOLYLINE object
  • so you can take advantage of the LWPOLYLINE features without having to learn how to use the Pline command.

Each segment must end precisely where the next segment begins or you will not be able to Join segments using Pedit

so you should use Endpoint osnaps if you create individual LINE & ARC objects to create LWPOLYLINEs using Pedit.

You can use the Rectang command to quickly create closed LWPOLYLINE objects that are rectangular in shape.

  • you are prompted for two corner points and you can also specify a fillet radius to use in each corner.

  • The Donut command creates circular LWPOLYLINEs & you can specify the width of these objects using inner & outer diameters.
  • if inner & outer diameters are the same then width is zero

  • if the inner diameter is zero the LWPOLYLINE is a filled circle.

You can use Polygon to create LWPOLYLINEs to form a perfect polygon shape (equal length segments) with up to 256 sides.

  • specify the radius & center of a circle that the polygon would be either inscribed in or circumscribed about

  • or specify the two end points of one Edge instead.

Any LWPOLYLINE can be converted to individual LINE or ARC segments with the Explode command.

  • all width information would be lost because LINE & ARC objects do NOT have width (only Lineweight for plotting purposes).

For example, if you EXPLODE a donut created with an inner diameter of zero you would get two ARCs that form a circle.

These ARC objects would lie on the center line of the original LWPOLYLINE object.

PRACTICE CREATING & EDITING LWPOLYLINEs

1) Close the drawing from the previous exercise (if it is open).

2) Pick File + New and select the Start from Scratch button. Select English as the Default Settings and pick OK.

In this drawing you will use PLINE to draw this shape as a LWPOLYLINE.
This shape could be that of an extrusion (e.g. protective molding strip)

3) Pick File + Save and use Extrusion.dwg as the File name and select your personal folder as the Save in location.

4) Pick Tools + Run Script. Select your personal folder to Look in and select T105.scr as the script File name. Then pick the Open button to run this script.

5) Left-click on the POLAR and OSNAP status bar buttons to turn these drafting tools On.

6) Pick Format + Drawing Limits. Press <enter> to use 0,0 as the lower left corner and enter 1,1 as the upper right corner.

7) Pick View + Zoom + All to zoom in on these new limits.

8) Pick Draw + Polyline. Enter 0.1,0.1 as the start point. Type 0.8 at the keyboard. Move your crosshairs to the right and press <enter> when the Polar tooltip angle is 0 degrees.

9) Create the next four LINE segments using direct distance entry again with the distances shown below in either exactly horizontal or vertical directions.

10) Right-click in the drawing area to invoke a shortcut menu and select Arc. Right-click in the drawing area again to invoke another shortcut menu and select CEnter.

When you invoke the Pline command you begin in Line mode by default but you can switch to Arc mode at any time.

  • if you switch to Arc mode your command line options are specific to ARC segments.
  • you remain in Arc mode unless you explicitly select Line mode.
  • you return to Line mode again the next time you use Pline.

11) At the prompt for the Center point enter @0.4<180. Then move your crosshairs to the left and left-click when the Polar tooltip angle is 180 degrees to supply the end point of this ARC segment.

12) Right-click in the drawing area to invoke a shortcut and select Line to switch back to Line mode.

If you do NOT switch back to Line mode the next segment you make would be an ARC (instead of the desired LINE).

  • the next ARC segment would also have been automatically tangent to the last ARC segment if you picked an end point.

13) Use direct distance entry again to create the next three LINE segments in either horizontal or vertical directions using the distances shown below.

14) Right-click in the drawing area to invoke a shortcut and select Close to complete this closed LWPOLYLINE.

LWPOLYLINEs can be closed or open (open means the end does not join with the start)

  • you just created a closed LWPOLYLINE and you know that it is closed because you selected the Close option.

You could make the same shape by using an Endpoint osnap at the start of the LWPOLYLINE and pressing <enter> to terminate Pline

  • however, AutoCAD considers LWPOLYLINEs to be open unless you explicitly use the Close option to terminate Pline.

15) Pick Modify + Polyline and select any part of the LWPOLYLINE you just created. Right-click in the drawing area to invoke a shortcut and select Width. Enter 0.01 as the width for all segments and press <enter> to complete and exit the Pedit command.

Now all segments of this LWPOLYLINE are 0.01 drawing units wide but you should NOT confuse this width with Lineweight

  • Lineweight is an object property that can be applied to any 2D object and it determines how objects appear when you Plot
  • width can ONLY be applied to LWPOLYLINE objects.
  • you can edit width of individual segments by using the Edit Vertex option (and it’s associated set of options).

16) Pick Modify + Explode and select the LWPOLYLINE. Then press <enter> to complete this command.

Width information is lost after you EXPLODE this object & now you have a collection of individual LINE and ARC objects.
These are the same object types you would get if you used LINE & ARC commands.

17) Pick Tools + Inquiry + List and select the ARC segment. Then press <enter> to continue. Read the report to verify that this is an ARC and press F2 to switch back to the drawing window.

18) Pick Modify + Polyline. Select the ARC segment and AutoCAD will tell you that the selected object is not a Polyline and ask you if you want to convert it to a polyline. Press <enter> to accept <Y>. Right-click in the drawing area to invoke a shortcut & select Join. Then select all of the other LINE segments & press <enter> to join them together. Press <enter> to complete and exit Pedit.

If you had used Line & Arc to make these individual objects you could have converted them to a LWPOLYLINE in the same way.

  • now the shape in your drawing is a LWPOLYLINE again and you can manipulate it like a LWPOLYLINE created with Pline.

19) Pick Draw + Region and select the LWPOLYLINE. Then press <enter> to complete Region.

20) Pick Tools + Inquiry + Mass Properties and select the new REGION object. Press <enter> to display a report for this object. Read the report and press <enter> to return to the drawing window.

21) Pick Draw + Solids + Extrude. Then select the REGION object and press <enter> to continue. Enter 5 as the height and press <enter> at the prompt for taper angle to use the default of 0 degrees.

22) Pick View + 3D Views + SE Isometric to view the extruded shape from an isometric viewing direction.

LWPOLYLINE objects are useful in 3D modeling

23) Pick File + Save to update your changes to Extrusion.dwg.

24) Pick File + Close.

25) Pick File + New and select Start from Scratch. Select English as the Default Settings and pick OK.

When you complete this exercise your drawing should resemble this solar collector model.

26) Pick File + Save and use Collector.dwg as the File name and select your personal folder as the Save In location.

27) Pick Draw + Rectangle. Enter 0,0 as the first corner and 4.25,5.5 as the opposite corner.

28) Pick View + Zoom + Extents.

29) Pick Draw + Circle + Center,Diameter. Enter 2,3 as the center point and then enter 1 as the diameter.

The rectangle could represent the edges of a letter size sheet if you were to plot the model tab of this drawing at a scale of 2:1.

This CIRCLE is not part of the model but you will use it to prove to yourself that the hexagon you are about to create is the right size.

30) Pick Draw + Polygon. Enter 6 as the number of sides. Enter 2,3 as the center point. Press <enter> to use the default Inscribed method and then enter 0.5 as the radius.

The new hexagon is perfectly inscribed inside the CIRCLE

31) Right-click in the drawing area to invoke a shortcut and select Repeat Polygon.

32) Press <enter> to use 6 sides again. Right-click in the drawing area to invoke a shortcut and select Edge. Use Endpoint (or Intersection) osnaps near P1 then P2 (in that order) to supply the first & second end points for the edge.

33) Create the remaining hexagons shown below on your own using a similar technique.

34) Pick Draw + Donut. Enter 3 as the inner diameter and 3.1 as the outer diameter. Use a Center osnap on the CIRCLE as the center point. Then press <enter> to complete and exit the Donut command.

35) Select the inner CIRCLE with no command running and press the Delete key to Erase it.

36) Pick File + Save to update your changes to Collector.dwg.

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