POLYLINEs, which are 2 dimensional drawing objects, are made up of pieces of lines and arcs called segments. Points where these segments are joined together are called VERTEX and all vertices lie on the same plane. All Z coordinates for all the points are the same as the first Z coordinate specified for the first point. All segments making up the POLYLINE act as one. All the features POLYLINE packs make it one of the most useful drawing tools in AutoCAD.
Tip: As all the vertices of a POLYLINE object lie on the same plane, you can safely use it to draw planar cross-sections and profiles in 3 dimensional drawings. Moreover, as it has properties like it's perimeter and area, you can use it frequently in your quantity surveys.
Using the command: Using the command is mostly command prompt based. You therefore need to keep an eye on the command prompt whenever using the command.
Command: _PL [ENTER]
Specify start point: 0,0
Current line-width is 0.0000
Specify next point or [Arc/Halfwidth/Length/Undo/Width]:750,0 [ENTER]
Specify next point or [Arc/Close/Halfwidth/Length/Undo/Width]:750,500 [ENTER]
Specify next point or [Arc/Close/Halfwidth/Length/Undo/Width]: [ENTER]
Follow the sequence above and create a simple POLYLINE object. Try moving and copying the object. This will help you get a better understanding of how the object behaves. Now let's have a closer look at what happened in the command line.
1) Specify start point: As is the case with all objects, this object also needs a start point. Specify on screen with the mouse or specify a point with the keyboard.
2) Current line-width is 0.0000: AutoCAD is giving us some information about the width of the POLYLINE we are drawing. As we can understand from here, this object has a width value. A value of 0 width means a line.
3) Specify next point or [Arc/Halfwidth/Length/Undo/Width]: We create the first segment by specifying the next point. More about the options later.
4) Specify next point or [Arc/Close/Halfwidth/Length/Undo/Width]: We create the second segment by specifying the next point once again. Just like with the LINE command, joining the first and the last points can end the command. At this stage, we understand that POLYLINE objects can have open or closed geometries. Both have their own uses.
As you can see, using the command is pretty straightforward. Now let's take a closer look at the properties of the POLYLINE object.
Vertex: As we mentioned earlier, the corner points of a POLYLINE are each called a VERTEX. Open POLYLINES' number of vertices are 1 greater than the number of segments, while these numbers match on closed POLYLINE objects.
Start/End segment width: Segments within a single POLYLINE object may have different width values. Segments can even have different starting and ending widths. You can start playing with different values to check this out.
Area/Length: All POLYLINE objects contain information on their closed area and the total length of its segments. These values will be displayed in your drawing units. Areas of open POLYLINE objects are calculated as if the first and the last vertex points are joined by a straight line. However, the length given is the length of the open polyline. In our example, the area has been calculated just like a triangle's area (750x500/2).
Closed: This will be defined as "No" for open POLYLINE objects and "Yes" for closed ones. Sometimes, though the starting and ending points of a POLYLINE object may seem to coincide and thus be a closed object, they may just be placed very close together and still constitute an open object. However, POLYLINE objects with their "Closed" property defined as "No" are open objects and cannot be used in 3D commands such as EXTRUDE, REVOLVE etc.
Linetype Generation: This value is controlled by the PLINEGEN system variable. This is "Disabled" for POLYLINEs generated with the variable PLINEGEN set as "0" and "Enabled" for POLYLINEs generated with the variable set at "1". This value is important for POLYLINEs drawn with non continious line types.
When "Linetype generation" is "Ebabled", the POLYLINE is perceived as a whole and the line type is constituted as follows. With the "Disabled" setting, however, each segment is considered individually and the line type is constituted accordingly.
Prompt List: (This section of the article has been prepared using AutoCAD help files).
1) Next point: Draws a line segment, previous prompt is repeated.
2) Arc: The segment drawn with this option selected will be an arc. Therefore, arc options will also be included in the command prompt.
Specify endpoint of arc or [Angle/CEnter/CLose/Direction/Halfwidth/Line/Radius/Second pt/Undo/Width]:
You will see that an arc will be drawn with the point you specify. While 3 points are normally needed to construct an arc, here it seems like just 2 points are enough. The reason behind this is that the arc will be constructed as being tangent to the previous line segment. Most importantly, the POLYLINE will be constructed anti-clockwise. You'll thus not have difficulties constructing arcs. If you wish to construct the arc within the PLINE command concentric with an existing arc or circle (OSNAP) you should use the CEN shortcut. The "Angle" option helps you specify the angle suspended by the arc, "Direction" the starting direction of the arc, "Radius" the radius of the arc and "Second pt" helps you specify another point on the arc. These options work just like the way they do in the arc command. The command switches back to arc mode with the "Line " option.
3) Close: Draws a line between the first and last drawn points of the POLYLINE, making it a closed object (i.e. closing the POLYLINE). The command ends with this optin. To be able to use this option, you must have specified at least to points.
4) Halfwidth: If you'd like to draw a wide segment, you can define the width by entering the distance between the axis and the edge of the POLYLINE. The total width will be double this value.
Specify starting half-width <0.0>: 20
Specify ending half-width <20.0>:
All segments may have different starting and ending widths. The starting and ending values will be matched to the values you specify here.
5) Length: Constructs a line segment in the same direction as the previous one and in the length you specify. If the previous segment is an arc, the line constructed will be tangent to the said arc.
6) Undo: Undo the previous segment.
7) Width: You can specify starting and ending width values for the current segment you are drawing.
Related Commands:
Relevant System Variables:
FILLMODE: Controls the filling of thick segments. HPBOUND: Specifies whether objects created using the BOUNDARY command are constructed as REGION (0) objects or as POLYLINE (1) objects. PLINECONVERTMODE: Controls whether segments are converted as lines (0) or as arcs (1) when converting SPLINE objects to POLYLINE objects. PLINEGEN: Controls how line styles are aligned if you are using line types when drawing POLYLINEs. Please see the section headed "Linetype generation" in our article. PLINETYPE: The value of this variable is stored in the Windows registry file and they are applied for all drawing files. It controls whether old POLYLINE types can be converted to the new type when older drawings are accessed. The new POLYLINE type is optimized and takes up lesser space. When this value is set as 0, the old type is used when older drawings are accessed or new ones created. When the value is set at 1, older ones are not converted but new creations are done using the new type. When the value is at 2, both the old ones are converted and the new ones are created with the new version. PLINEWID: This variable, which is stored inside the drawing controls the default segment width. The last value you used is stored here and is applied as the default value for new drawings.System variables mentioned in this article: FILLMODE, HPBOUND, PLINECONVERTMODE, PLINEGEN, PLINETYPE, PLINEWID.
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