GAF

Surveying Mathematics Made Simple

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Version 1.0.0

Grid Adjustment Factor

Start

(a.k.a. Combined Factor)

Grid Adjustment Factor

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Ground to Grid

Grid to Ground

Coordinates to GAF

GAF Comparison

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(a.k.a. Combined Factor)


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Ground Northing

Ground Easting

GAF

(1/X)

Origin Northing

Origin Easting

OUTPUT

Grid Easting

Grid Northing

Back

Calculate

Reset

NOTE: The GAF will normally be less than 1 (i.e. 0.99995678). For locations near the outside edges of the zone, the GAF can be greater than 1. (i.e. 1.00001234). Be sure to verify the GAF before applying.

Grid Northing

Grid Easting

GAF

Origin Northing

Origin Easting

OUTPUT

Ground Easting

Ground Northing

Back

Calculate

Reset

(1/X)

Ground Northing

Ground Easting

Grid Northing

Grid Easting

OUTPUT

N-GAF

(1/X)

E-GAF

(1/X)

Back

Calculate

Reset

GAF-1

(1/X)

GAF-2

(1/X)

Distance

OUTPUT

Distance-1

Distance-2

Back

Calculate

Reset

The GAF (a.k.a. Combined Factor) on the NGS data sheets are shown as ground to grid values when using the following formula:

Grid coordinate = Ground coordinate x GAF (Origin 0,0)

The GAF can also be shown as Grid to Ground value such as: 

Ground coordinate = Grid coordinate x GAF (Origin 0,0)

In this case the GAF = 1 /  GAF(NGS)

It is very important to apply the correct GAF with the right formula. 

If a GAF is shown as 1.000xxxxx then it maybe outside of the zone limits. This needs to be verified before applying to your project. If available, a review of a nearby NGS control point will aid in resolving the proper use of the GAF.

Ground to Grid  

Enter the Ground Northing coordinate 

Enter the Ground Easting coordinate 

Enter the project GAF. Be sure to use the correct value for the GAF. 

The Origin defaults to Zero for the Northing and Easting. If your project has a different Origin, enter the Northing and Easting.  

Tap “Calculate” to convert the Ground Coordinates to Grid Coordinates.   

Tap “Reset” to clear the fields.  

Tap “Back” or “Close” to return to the prior screen.  

See the companion book “Coordinate Transformation” for formulas and procedures for converting between coordinate datums.

Grid to Ground

Enter the Grid Northing coordinate

Enter the Grid Easting coordinate

Enter the project GAF. Be sure to use the correct value for the GAF. 

The Origin defaults to Zero for the Northing and Easting. If your project has a different Origin, enter the Northing and Easting.

Tap the “Calculate” button to convert the Grid Coordinates to Ground Coordinates. 

Tap the “Reset” button to clear the fields.

Tap the “Back” or “Close” button to return to the prior screen.

See the companion book “Coordinate Transformation” for formulas and procedures for converting between coordinate datums.

Coordinates to GAF

Use this tool to determine the GAF given the Ground and Grid Coordinates.

Enter the Ground Northing.

Enter the Ground Easting.

Enter the Grid Northing.

Enter the Grid Easting.

Tap the “Calculate” button to determine the GAF using both the Northing and Easting coordinates. They should be the same or very close to the same.

This tool is useful when the GAF is not shown on a drawing and you have both coordinate datums for determining the GAF. The origin is 0,0.

Tap the “Reset” button to clear the fields.

Tap the “Back” or “Close” button to return to the prior screen.

GAF Comparison

Use this tool to compare two GAF values to determine how they affect the overall distance when measuring on the ground with conventional survey equipment. 

This comparison is useful when comparing a project GAF with a published GAF such as those shown on NGS data sheets.

Written by Surveyors for Surveyors, Engineers and aspiring Students.

Author/Programmer: Jim Crume P.L.S., M.S., CFedS

www.cc4w.net

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Written by Surveyors for Surveyors, Engineers and aspiring Students.

Author/Programmer: Jim Crume P.L.S., M.S., CFedS

www.cc4w.net

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I have several decades of land surveying and civil engineering experience. I was first licensed in 1983 in Wyoming and Utah. In 1986 I became licensed in Arizona. I was appointed a United States Mineral Surveyor in 1986. I have been practicing Land Surveying in Arizona since 1990. I became a Certified Federal Surveyor in 2007. I have several decades of computer programming experience related to computer aided drafting and coordinate geometry. I am the pioneer in the use of Digital Signatures in Arizona for professional documents.

Jim Crume P.L.S., MS, CFedS