Methods of obtaining contours - WordPress.com · m is the horizontal map distance from A to M (cm)...

Methods of obtaining contours

CE 221 ‐ Higher Surveying

By estimationBy estimation

• Suitable for small scale maps where the ground p gform is not too irregular

• The process is fast and produce reasonable results when done carefullyresults when done carefully

• Steps:– Make a careful study of the position of the contourMake a careful study of the position of the contour points and try to visualize the changes in slope of the terrainDraw the contours which appear to be most definitely– Draw the contours which appear to be most definitely located by the plotted points; index contours are usually drawn first which will act as guides for the intermediate contoursintermediate contours

3Prepared by: Andre‐Paul C. Ampong

Rubber band methodRubber band method

The rubber band should have sufficient width so that graduations at equal intervals can be marked on it to form some kind of an elastic scale. 4Prepared by: Andre‐Paul C. Ampong

Rubber band methodRubber band method

The rubber band is stretched between two plotted points so that p pthese points fall at scale divisions corresponding to their elevations 5Prepared by: Andre‐Paul C. Ampong

Variable scalesVariable scales


Analytical methodAnalytical method


Analytical methodAnalytical method• By similar triangles:

Where:DEH

dehm =

Where:A & B are established points on the

ground of known elevationM is a point on a contour crossing p g

the line between A and Bhm is the horizontal map distance

from A to M (cm)de is the difference in elevationde is the difference in elevation

between M and A (m)DE is the difference in elevation

between A and B (m)H is the horizontal map distance

between A and B (cm)8Prepared by: Andre‐Paul C. Ampong

Triangle and scale methodTriangle and scale method



Elev = 296.9m

El 245 5Elev = 245.5m

GiGiven:Elevation of point “a” = 245.5 mElevation of point “b” = 296 9 mElevation of point b = 296.9 mContour Interval = 20.0 m



Elev = 296.9m

El 245 5Elev = 245.5m


Template methodTemplate method



• Sample problemSample problem

i d i d i l b i dIt is desired to interpolate between points X and Y the position of the following contours: 161, 162 163 164 d 165 Th l i f X d162, 163, 164 and 165. The elevation of X and Y are respectively 160.9 m and 165.4 m.



Y (Elev = 165 4 m)Y (Elev = 165.4 m)5.4

165 m

163 m

164 m

162 m

X (Elev = 160.9 m)0.9

161 m



• Sample ProblemSample Problem

l d d hAssume two plotted ponts A and B have elevations of 117.5 m and 125.8 m,

i l I i i d lrespectively. It is required to locate contours 120 and 125 using a template of converging lilines.



A (Elev = 117.5 m)

B (Elev = 125.8 m)



A (Elev = 117.5 m)

01

B (Elev = 125.8 m)1

23

45

677

8



A (Elev = 117.5 m)

01

B (Elev = 125.8 m)

12

34

56

7 88


Methods of obtaining contours - WordPress.com · m is the horizontal map distance from A to M (cm)...

Documents

Transcript of Methods of obtaining contours - WordPress.com · m is the horizontal map distance from A to M (cm)...