Estimating Sheet

# How land surveyors compute scale factor in surveying

Construction Software

In this construction article one will learn how to work out scale factor. The article is specifically useful for land surveyors.

Surveyors take care of small but vital modifications to their field surveys constantly. The surveyors should have sound knowledge on how the scale factor utilized with field observations and office calculations is vital while handling grid coordinates i.e. Map Grid of Australia (MGA94). The challenge for surveyors is to apply GPS devoid of misinterpretation what the scale factors are. It will turn out to be more complex while introducing a Total Station that creates ground distances, incorporated with GPS. It forms coordinates which are associated with a predefined datum.

A map projection offers an ideal way of illustrating the curved surface of the earth on a plane surface in order that coordinate grids are described and maps are drawn. The relative positions of points on the grid are partly modified from their ground positions because of applying Transverse Mercator Projection to form the curvature of the earth.

The formula for the scale factor is given as :-

Scale Factor = Grid Distance/Measured Distance (at MSL)
As for instance, choose these two coordinates

• A=1882281.927 , 182474.093
• B=1882314.193 , 182458.059
• The grid distance (measured distance) on the map is provided as 36.03
• Namely √((1882281.927 -1882314.193)²+(182474.093-182458.059)²)=36.030

• If you estimate the horizontal distance among A&B in ground with tape or Total station and got 36.000 m. Then the scale factor will be computed as
• Scale Factor=Grid Distance/Measured Distance (at MSL)
• Scale Factor=36.030/36.000
• Scale Factor=1.000833
• Otherwise, the computation can be done for the ground distance from the above plan
• The ground distance among point
• 1 to 2 =36.03/1.0008428=36.00