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UP LAYERS AND ENTITY MODES
Select LAYER CONTROL in the SETTINGS menu, and create a set of layer names, e.g. 1granite, 1granith, 2diabase, 2diabash, 3sand, 3sandh, 4lime, 4limeh, by typing in the rock name (e.g. 1granite) on the name box beneath the NEW button, and clicking the NEW button. Also, create a `rectangle' layer in which to draw a bounding rectangle. The names will be arranged alphabetically. The layer `1granite' will contain all granite entities that you draw , and the `1granith' layer the hatch fill for that entity, etc. Click the 1granite and 1graniteh layers (they will become highlighted) and click off any other layers already highlighted. Click the set colour button and click on the standard red button to set the `1granite' and `1granith' layers to the colour red. Repeat this operation, designating a different colour for each rock type [DIABASE (blue), SANDSTONE (yellow), LIMESTONE (CYAN), and the bounding RECTANGLE (MAGENTA)]. Make `1granite' the current layer by clicking the CURRENT button, and exit the LAYER CONTROL menu. Select ENTITY MODES in the SETTINGS menu. Set the COLOUR and LINE THICKNESS to BY LAYER, and enter a value of `1' for the ELEVATION. All objects will now be drawn in the COLOUR and LINE THICKNESS set in the LAYER menu, and all granites drawn on the granite layer will be designated a topological value of `1'. (The entity properties can be changed by clicking MODIFY, CHANGE, Points, Select objects `ENTER', and typing (P)roperties-'ENTER', (E)levation `ENTER', and giving the drawn entity a new topological Z value; if necessary also type `t' `ENTER' to change the line thickness.)
DRAWING LINES and SKETCHING
Lines can be drawn as straight line segments or sets of connected straight line segments in either polyline or sketch mode. The thickness of the line is represented as a `Width' rather than a `Thickness'. In polyline mode (`pl' `ENTER') the length of the segments can be varied as the lines are drawn, whereas in sketch mode the length of the segments are pre-defined. If using sketch mode, first set SKPOLY to a non-0 value by typing `skpoly' `ENTER' `1' `ENTER', and then `SKETCH' `ENTER'. (Note: P = Raise/lower pen; C = connect; E = erase; .(period) to draw a line from last end point to new location of pointer when the pen is up; R = record lines drawn so far; X = records and exits; Q = quit. Check disk space from time to time with `STATUS'.) If SKPOLY= 0 the lines drawn in SKETCH will be composed of individual line segments rather than a continuous sequence of linked polyline segments. In other words clicking on the line will only select the line segment and not the the polyline. Having pressed `p', move the cursor to generate a sketched polyline. Press `p' to terminate the sketch and `X' to exit and save the SKETCH. If drawing an irregular closed area, it will be necessary upon exit from SKETCH to join the end points of the polyline to create a closed polyline. Type `PEDIT' `ENTER', select the object, and type `C' `ENTER' `ENTER'. An additional line segment will be added to the line joining the end point nodes of the line, and the line will be closed. Alternatively, choose `ENTITY' in the MODIFY menu, click the sketched entity and click the `polyline closed' button. The polyline will be automatically closed.
To join polylines:
1) in the case that a 2nd polyline is to be joined to a previously drawn polyline as the 2nd polyline is being drawn; a) On the AutoCad command line, type `OSNAP' `ENTER', and response to the prompt `Object snap Modes', type `endpoint' `ENTER'. b) Draw the 1st polyline by typing `pl' `ENTER' and clicking the left mouse button to generate a set of nodes delineating the polyline. c) When finished, press ENTER and again enter `pl' to begin drawing the second polyline. The cursor cross hair should now have an object snap box located at the intersection of the cross hairs. (The size of the object snap box can be set by selecting OBJECT SNAP in the SETTINGS menu.) Place the box over the end point of the 1st polyline and click to locate the beginning node of the polyline. When the line is completed, type `pedit' `ENTER', click on one of the lines, type `j' (for join) `ENTER'. Click the two polylines to be joined. The two polylines will be combined into a single polyline.
2) in the case both lines have already been drawn and are separated by a gap. a) If `Grips' has not already been turned on, type `grips' `ENTER' and in response to the prompt `New Value for Grips ' enter a value of `1' to turn the grips mode on. Clicking a polyline will cause the nodes to be displayed. Click and drag the end node of one of the lines to the end node of the other line. Since OSNAP endpoint is in operation, the two end points will be exactly superimposed, and can be joined using `pedit' `ENTER' `j' `ENTER' `ENTER'. To clear the `grips' press Ctrl-C twice. If in joining the lines you create a polygon object, the object will be automatically closed. To convert polylines to polygons use BPOLY.
To replicate a closed or unclosed (segments not joined) polyline object, or to create a `polygonal' object defined by a set of intersecting polylines (e.g. draw four intersecting polylines), type `bpoly' `ENTER'. Click the `Pick Points' button in the Polyline Creation dialogue box, and click inside the polygon defined by the intersecting lines.
(NOTE: if the dimensions of the map are large, for example UTM coordinates of 476900, 4760000 to 478700, 4762500 (1800 m by 2500 m), BPOLY will tell you when you click inside the area that 'The point is outside the boundary'. In this case it is necessary to move the diagram to the base coordinate of 0,0 using MOVE, before using BPOLY.) There now exists two entities, the copied `polygon', and underlying closed polyline. To remove the latter, MOVE the polygon to expose the polyline, and then ERASE it. Or, copy the polygon to a new layer using the CHANGE function, and then ERASE the polyline. Or, do not close the polyline when drawing it, but draw the last segment of the line through and beyond the beginning node. When you create the BPOLY polygon, the segment extending beyond the final node will still be visible, and can be selected to erase the underlying polyline. Note that the object created with BPOLY will NOT automatically take on the Z (Elevation) of the layer objects as set in Entity modes. The Elevation value must be changed using MODIFY, CHANGE, Points, Select objects `ENTER', and typing (P)roperties-'ENTER', (E)levation `ENTER', and giving the drawn entity a new topological Z value; if necessary also type `t' `ENTER' to change the line thickness.
Figure 1. Plate Tectonics.
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