Subject: Mapping Contours in ACAD, how to, by Merrick
From: merrick group <merrickgroup(--nospam--at)compuserve.com>
Date: Thu, 4 May 2000 14:46:37 -0400
Instructions to draw a contour map in Autocad. I am using ACAD14.
1) Draw Survey points (Draw/Point) z = elevation. (x,y) can be located
in plan with your mouse and later adjusted for elevation
2) Draw Landscape lines, if needed, between points, (Tools/Object snap
settings / node)
a) Extrapolated contours can be done by enlarging the line between
the two points with a reference at its midpoint. (Modify/Scale/Select
object/ base point = (Draw/Object-snap-settings/midpoint))
b) To clarify: If a contour is to pass between two points then the
contour is interpolated, and no line is needed.
3) Draw the contour face, this to be the flooded water level for
locating contours (Draw/Surfaces/3Dface) use four points z default is 0.
Place boundaries beyond the image needed. Move the face to the desired
elevation by modifying the Z coordinates to one elevation.
(Modify/Properties/select 3Dface) This same face can be used for other
4) Draw Landscape faces (Draw/Surfaces/3Dface) between ends of Landscape
lines or between nearest the nodes of the elevation survey. Mostly
landscape faces are defined by the nearest reference nodes lines (object
snap settings / node) or ends of extended lines (object-snap-settings/end)
and are sloped. The snap command might turn off at initializing the 3Dface
command and needs to be reset.
5) Run the render function (View/Render) this will shadow the shapes to
approximate the contour to be defined.
a) Alternatively, run the Hide option. (View/Hide) this will look
like cut off lines that represent the joining edges of landscape faces. It
will not shadow in the cut edges of the landscape faces. Be sure what you
see is not a line, they don't cut off.
b) I have found that lines alone will not be cut from view. If a
short length is visible then the whole line is visible, so there must be
3Dfaces to view where the contour line is to be located.
6) Draw P-line contours (object snap settings / none) (Draw/Polyline)
select points at corners and to either side of corners to estimate the
width of a valley or ridge.
a) Selecting the corners only, the curve-fitting of the P-line will
cause large doughnuts to fly out beyond a realistic contour profile.
b) If points are only placed at corners and mid-points then the
curves will be too sharp.
7) Remove shade (View/Regen)
8) Modify P-line to curve. (Modify/Properties/curve-fit) pick the
contour P-line and choose (curve-fit).
9) Move P-line from Z = 0 to proper elevation, or leave it at zero for a
2D drawing. (Modify/Properties) pick P-line and change Z coordinates to
I want new ideas for this method. I plan to set up a program to down load
coordinates and automate some of the above with macros. Shall I here from
David B. Merrick, SE