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Gale's table, coordinates of all points

Short answer

Using Bowditch rule from C (1000N,1500E), coordinates are: A (972.637N, 1333.995E), B (1030.036N, 1367.756E), C (1000.000N, 1500.000E), D (993.467N, 1565.935E), E (920.688N, 1542.047E). Linear misclosure 0.3657 m, 1/1530.

Prepare the Gale's Table and find the co-ordinates of all the points if the co-ordinate of C is (1000N, 1500E) from the following data.

S.NoLineLength (m)Bearing (WCB)
1AB66.6030°30'
2BC135.70102°48'
3CD66.3095°40'
4DE76.60198°8'
5EA214.30284°1'

The bearings are given directly, so the Gale's table starts from the latitudes and departures. Bowditch's rule is used to balance the traverse, and the coordinates are then run from C (1000 N, 1500 E).

Step 1: Latitude and departure

Lat=Lcos⁡θ,Dep=Lsin⁡θ\text{Lat}=L\cos\theta,\qquad \text{Dep}=L\sin\theta
LineLength (m)BearingLatitudeDepartureCorr. latCorr. dep
AB66.60030°30'+57.385+33.802+0.0140-0.0412
BC135.700102°48'-30.064+132.328+0.0285-0.0840
CD66.30095°40'-6.547+65.976+0.0139-0.0410
DE76.600198°08'-72.796-23.840+0.0161-0.0474
EA214.300284°01'+51.904-207.919+0.0450-0.1327
Sum559.500-0.117+0.346+0.1174-0.3464

Step 2: Closing error

eN=ΣLat=−0.117 m,eE=ΣDep=+0.346 me=eN2+eE2=0.3657 mRelative error=eΣL=0.3657559.50=11530\begin{aligned} e_N&=\Sigma\text{Lat}=-0.117\ \text{m},\qquad e_E=\Sigma\text{Dep}=+0.346\ \text{m}\\ e&=\sqrt{e_N^2+e_E^2}=0.3657\ \text{m}\\ \text{Relative error}&=\frac{e}{\Sigma L}=\frac{0.3657}{559.50}=\frac{1}{1530} \end{aligned}

Step 3: Bowditch correction

Clat=−eNLΣL,Cdep=−eELΣLC_{lat}=-e_N\frac{L}{\Sigma L},\qquad C_{dep}=-e_E\frac{L}{\Sigma L}

The corrections are in the last two columns above (their sums cancel the errors). Adjusted values:

LineAdj. latAdj. depAdj. length (m)Adj. bearing
AB+57.398+33.76166.59130°28'
BC-30.036+132.244135.612102°48'
CD-6.533+65.93566.25895°39'
DE-72.780-23.88876.599198°10'
EA+51.949-208.052214.440284°01'

Step 4: Coordinates of all points

Starting from C = (1000.000 N, 1500.000 E), add the adjusted latitude and departure of CD, DE, EA and AB in turn:

StationNorthing (m)Easting (m)
A972.6371333.995
B1030.0361367.756
C1000.0001500.000
D993.4671565.935
E920.6881542.047

Check: B plus the adjusted BC returns exactly to C (1000.000 N, 1500.000 E).

Answer: A (972.637 N, 1333.995 E), B (1030.036 N, 1367.756 E), C (1000.000 N, 1500.000 E), D (993.467 N, 1565.935 E), E (920.688 N, 1542.047 E); misclosure 0.3657 m, 1 in 1530.

✓ Answer checked by Claude Opus 5.5 (high effort)

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