mcl civil eng'g: How to Interpolate a Contour Map the AutoCAD way.

The coordinate-method is one way of drawing a contour map. Surveyors start at a certain reference point and indicate points on locations that are of an increment distance away from the reference. In this example,

points are incremented by 10 meters from the reference. The elevations at each point are measured and tabulated. Point A1 is the reference and has a coordinate of (0, 0, 1522.82). Point A2 has a coordinate of (10, 0,

1559.25), point B1 has a coordinate of (0, -10, 1440.00), etc.

To draw the contour map using the spline-loft method of Autocad, use first the 3dmesh command.

Type 3dmesh in the command line. Then from there you will be asked what of what size will your mesh be in the M direction. This will be the number of coordinates you will have on the x-axis direction. For this

example input 6. Then for the N direction, input 7.

After that you will be asked for the locations of vertices. These are the coordinates of each point and there are 6x7 coordinates/vertices in this problem.

the first vertex is point A1. Input for the first vertex: 0,0,322.82

Why 322.82? The vertical reference elevation for this problem is considered to be 1200 since the lowest point on the map is 1290.56. Any reference elevation can be used but it will be best if it is lower than the lowest

elevation and divisible by 100 (which is the index cotour). 322.82 came from the difference between the point elevation of A1 and the reference elevation.

When asked for the second vertex, it should be B1 because the arrangement of input for a 3dmesh is [M][N]

the second vertex should be 0,-100,240

100 is used instead of 10 to increase the horizontal scale of the map by a factor of ten. It would make the appearance of the final mesh clearer.

next, input the coordinates of C1 (C1 is 0,-200,195.45), D1, E1, F1, G1, A2 (A2 is 100,0,359.25), B2...

You can continue to input these values up to G6, or just start a new file and paste this on the command line:

3dmesh

Enter size of mesh in M direction: 6

Enter size of mesh in N direction: 7

Specify location for vertex (0, 0): 0,0,322.82

Specify location for vertex (0, 1): 0,-100,240

Specify location for vertex (0, 2): 0,-200,195.45

Specify location for vertex (0, 3): 0,-300,209.56

Specify location for vertex (0, 4): 0,-400,236.73

Specify location for vertex (0, 5): 0,-500,270.35

Specify location for vertex (0, 6): 0,-600,345.35

Specify location for vertex (1, 0): 100,0,359.25

Specify location for vertex (1, 1): 100,-100,241.32

Specify location for vertex (1, 2): 100,-200,225.68

Specify location for vertex (1, 3): 100,-300,253.68

Specify location for vertex (1, 4): 100,-400,279.15

Specify location for vertex (1, 5): 100,-500,320.44

Specify location for vertex (1, 6): 100,-600,365

Specify location for vertex (2, 0): 200,0,285.1

Specify location for vertex (2, 1): 200,-100,262.38

Specify location for vertex (2, 2): 200,-200,306.44

Specify location for vertex (2, 3): 200,-300,345.15

Specify location for vertex (2, 4): 200,-400,295.65

Specify location for vertex (2, 5): 200,-500,290.68

Specify location for vertex (2, 6): 200,-600,319.5

Specify location for vertex (3, 0): 300,0,213.45

Specify location for vertex (3, 1): 300,-100,251.65

Specify location for vertex (3, 2): 300,-200,280.37

Specify location for vertex (3, 3): 300,-300,260

Specify location for vertex (3, 4): 300,-400,251.3

Specify location for vertex (3, 5): 300,-500,265.4

Specify location for vertex (3, 6): 300,-600,290.23

Specify location for vertex (4, 0): 400,0,162.12

Specify location for vertex (4, 1): 400,-100,191.05

Specify location for vertex (4, 2): 400,-200,200.72

Specify location for vertex (4, 3): 400,-300,210.28

Specify location for vertex (4, 4): 400,-400,234.05

Specify location for vertex (4, 5): 400,-500,252.98

Specify location for vertex (4, 6): 400,-600,275.1

Specify location for vertex (5, 0): 500,0,90.56

Specify location for vertex (5, 1): 500,-100,140

Specify location for vertex (5, 2): 500,-200,171.58

Specify location for vertex (5, 3): 500,-300,193.19

Specify location for vertex (5, 4): 500,-400,230

Specify location for vertex (5, 5): 500,-500,258.16

Specify location for vertex (5, 6): 500,-600,270.75

Use ZOOM EXTENDS (Type Z *Enter* E *Enter*)

You can see a mat like figure on the screen.

Use the spline command. Type spl on the command line.

Click consecutively on the points of intersection from A1 down to G1. After clicking G1, press Enter three times.

Do the same for the range of A2 - G2, A3 - G3 up to A6 - B6.

Select the splines using the left-to-right rectangular selection method and give the splines a color of red.

Use again the spline command, this time to the horizontal coordinate ranges. Ex: A1 - A6, B1 - B6, G1 - G6

Slect the new splines and color them green.

Select SW Isometric on the view toolbar.

Delete the white colored mesh. Only the colored splines will be left.

Draw a rectangle with corners at (0,0,0) and (500,-600,0). Use ZOOM EXTENDS again if the figure is out of the boundary.

On the UCS2 toolbar drag down list select Front

Use the 3d orbit (command: 3dorbit) to adjust the view to something similar to the figure below. This is done so that the endlines of all green splines are seen.

Use the polyline command (command: pl). When asked which is the first point, click the left end of the first green spline (the one nearest to you). The next point is the corner of the rectangle directly under the left end of the green spline. The next point is the other corner of the rectangle (directly below the right end of the green spline). Then the last point is the right end of the green spline.

Repeat the same process to the succeeding green splines (The same corners of the rectangle are still the 2nd and 3rd point). Then delete the rectangle at the bottom.

Use the region command (command: reg). Select all green splines and polylines. Press Enter after selecting all. This time the green splines will be combined with the polylines and will be colored white again.

Draw a line from 0,0 to 0,0,60. Array this line with a column count of 6 and a row count of 1. The column offset should be 100

Use the loft command (command: loft). Select all regions (The combined green splines and polylines) then press enter.

After pressing enter, there will be choices. Choose Guides by pressing g then enter.
The guide curves are all the red splines and lines drawn under (which are arrayed). Press Enter.

Using the left-to-right rectangular selection method (or the quick select method). Delete all red splines and lines at the bottom. You will have a final block which is the simulated figure of the contour map in 3d.

The front UCS must still be active in the UCS2 toolbar. Draw a line from (-100, 0, -100) to (600, 0, -100). Extrude (Using extrude command, shortkey: ext) this line to the direction of the positive axis by 800.

Array the extruded line, with a row count of 19, a column count of 1 and a row offset of 20.

Press Front on the view toolbar.

Use slice command (command: sl). Select the Block (The contour block). Then press Enter.

In the options choose Surface by typing s then pressing enter. Select the 2nd level extruded line (The one above the original) then press enter.

Repeat the last two steps. Use slice, select the block, choose surface, but this time use the 3rd extruded line, 4th extruded line on the succeeding repetitions, up until the last extruded line (at the very top is used as the slicing surface).