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Document Properties

The document properties should be the first thing checked and filled when starting a new job. It contains properties and settings that affect the rest of job.

File -> Document Properties

Combined Scale Factor

Nullcad is designed around the idea that incoming data from a controller is in grid coordinates, and final plans and data are required to be coordinated. Conversely, distances are required to be plane distances and entered distances from existing plans are also in plane. Traditionally, data is scaled to plane after import from a controller for calculations and surveyors must rescale data back to grid to attain final coordinates.

Nullcad solves this by keeping your data in grid and using a global CSF to dynamically scale entered distances back to grid and show or label distances on geometry in plane. The scale factor can be entered manually in the General tab of the Document Properties window. You can also calculate a CSF by selecting and existing point in your document, normally a known control point.

Note: when calculating a CSF make sure the point used has a Z/Height.

NullCad uses the following formula for MGA (Map Grid of Australia) / UTM projections.

Formula

CSF = PSF × HSF

Where:

  • CSF = Combined Scale Factor
  • PSF = Point Scale Factor (accounts for map projection distortion)
  • HSF = Height Scale Factor (accounts for elevation above the ellipsoid)

Point Scale Factor (PSF)

PSF = 0.9996 + 1.23 × (E - 500000)² × 10⁻¹⁴

Where:

  • E = Easting coordinate (metres)
  • 500000 = False easting (central meridian offset for UTM/MGA zones)
  • 0.9996 = Central meridian scale factor (k₀) for UTM

PSF equals exactly 0.9996 at the central meridian (E = 500,000m) and increases as you move east or west.

Height Scale Factor (HSF)

HSF = 1 - (H × 0.1571 × 10⁻⁶)

Where:

  • H = Ellipsoidal height (metres)
  • 0.1571 × 10⁻⁶ ≈ 1 / 6,371,000 (approximation of 1/Earth radius)

HSF reduces distances as elevation increases, since higher points are further from Earth’s centre.

Where to configure it

The active CSF is set in the Document Properties and applied by all tools that take a distance.

Caveat

This formula is a simplified approximation suitable for most surveying work within a single UTM/MGA zone. For high-precision geodetic work spanning zone boundaries or requiring rigorous error bounds, use the full Transverse Mercator equations instead.