1. ST236 Site Calibrations with Trimble GNSS
Peter Mestemaker
Trimble Navigation
Westminster, Colorado

2. Agenda What is a site calibration? Calibration – how it works!
Control requirements
Interpreting results
Calibration scenarios
The agenda for this class is as follows:
An overview of the GPS site calibration.
An explanation of the parameters computed in the site calibration
An explanation of the control point requirements for a site calibration.
A discussion on interpreting the results of the site calibration
A guide to the project settings for the site calibration. For example, which settings to use for different calibration scenarios.

3. Section 1 – General Overview
Site calibration
Why do we need it?
What does it do?
How is it done?
How is it used?
This section of the course will give a general overview of the GPS site calibration, with emphasis on the functionality and purpose of the calibration. For example:
Why do we need the site calibration?
What does it do?
How is it used in practice?

4. Site Calibration – Why we need it
Why use a calibration?
GPS with grid coordinates
What is the purpose of the GPS site calibration?
To compute the relationship between:
WGS-84 geodetic coordinates
local grid coordinates
(preferred by most surveyors)

5. GPS Coordinates (WGS84) WGS84 Cartesian Latitude (φ) Longitude (λ)
Greenwich Meridian j l h Z X Y P
Equator
WGS84
Latitude (φ)
Longitude (λ)
Height (h)
Cartesian
(X,Y, Z)
GPS measures coordinates in the WGS84 datum.
WGS84 positions expressed as:
Latitude, Longitude and height, or
XYZ cartesian coordinates.
Height = distance above (or below) WGS84 ellipsoid.
Origin is coincident with the Earth’s center of mass.
X and Y axis - perpendicular to each other - in the equatorial plane.
Z axis - at right angles to the X,Y plane - coincides with the earth’s rotational axis.
The prime orientation axis (X) is the Greenwich Meridian.

6. Surveyors want grid (X) Easting (Y) Northing (Z) Elevation
vertical datum Z Y X
Surveyors prefer to work in a grid coordinate system
coordinates expressed as (X,Y,Z) or
Easting, Northing, and Elevation
Assumed local grid coordinates
origin is defined at the Earth’s Surface.
Pre-defined National Mapping datum
origin is defined at (or near) the surface of the reference ellipsoid.
X and Y axis are perpendicular to each other, in the Local Plane.
Z axis is perpendicular to the local plane.
Prime orientation axis (Y) is Grid North

7. Site Calibration – What it does
Compute transformation parameters
WGS84
grid
WGS84
Computes transformation parameters between measured WGS84 coordinates, and the corresponding grid coordinate values, for a set of survey control points
Grid

8. Site Calibration – How it’s done
Control (Grid)
Measure (GPS)
Match point pairs
Calibrate!
To calibrate a project, we required existing control points with grid (control) coordinates.
The surveyor measures these control points using GPS – to establish WGS84 coordinates.
The calibration is done by pairing the measured WGS84 coordinates with previously determined grid coordinates on the control points.

9. Site Calibration – How it’s used
Computes grid
WGS84 measured
Computes WGS84
Stakeout from grid
3D calibration parameters are applied to all other measured points for the same project – resulting in grid coordinates for these points as well.
Calibration parameters may also be used for construction stakeout purposes. In this case allowing the GPS receiver to determine WGS84 coordinates for a series of pre-determined (design) grid points.
In layman terms, the GPS site calibration is simply a coordinate transformation utility
used to compute the 3-D relationship between WGS84 (GPS) coordinates and any grid coordinate system.

10. Elements of the calibration Calibration parameters
Section 2 – How it works!
Coordinate systems
Elements of the calibration
Calibration parameters
This section will explain how the site calibration works.
We will discuss coordinate system details, including:
Datum transformation
Map projection.
We will also discuss the elements of the site calibration, including:
Horizontal adjustment
Vertical adjustment (with and without the geoid model).
We will also list the parameters computed in both the horizontal and vertical adjustments.

11. Coordinate System Transform WGS84 to grid Requires:
Datum transformation
Map projection
Mathematically impossible to directly compare WGS84 geodetic coordinates with control grid coordinates.
The WGS84 coordinates must first be transformed to grid coordinates, prior to comparing with exist grid control values.
This requires a coordinate system, consisting of:
Datum transformation
Map projection

12. WGS84 Local Ellipsoid Datum Transformation WGS84 to local ellipsoid
Not required if:
Local ellipsoid = WGS-84
Arbitrary local grid
Known parameters?
Use them!
Transforms WGS-84 coordinates to local geodetic coordinates - relative to the local ellipsoid.
Only necessary if the local map grid is projected from an ellipsoid other than WGS-84.
i.e. - coordinates in national or regional mapping datum.
Not required if calibrating to arbitrary local grid coordinates.
Published datum parameters are in Survey Controller and TGO – use them!

13. Projection to local grid
Map Projection
Projection to local grid
(φ, λ) (N, E)
Always required
Not specified?
default TM at project location
Projects geodetic coordinates to a plane surface – expressed as (N,E)
Map projection is ALWAYS used in the site calibration.
Choice of projection may be transparent to the user.
If calibrating to coordinates in a defined map projection
geodetic coordinates projected using the specified map projection.
If calibrating to an arbitrary local grid system
Map projection parameters are not defined.
Software creates a local (default) TM projection – with origin at the project area.
This step is transparent to the user.

14. Horizontal adjustment Vertical adjustment
Calibration Elements
Horizontal adjustment
Vertical adjustment
Geoid model
Adjustment parameters
The elements of the site calibration include:
Horizontal adjustment of projected grid coordinates to best fit the local control grid values.
Vertical adjustment of measured heights to best fit the local control elevations.
The vertical adjustment can be performed with (or without) a GEOID model
We will discuss the parameters computed in each of the adjustments

15. Horizontal Adjustment
2 coordinates per control
Measured (projected)
Control grid
Least squares adjustment
Rotation
Translations
scale
= GPS observation
= Control Point
We must have 2 sets of horizontal grid coordinate values for each control point in our calibration. These are:
GPS coordinates – transformed to local datum and projected to local grid, and
Control grid values – previously established.
This is an un-weighted least squares adjustment (paired with a 2D Helmert transformation) to determine the best fit between the measured coordinates, and the corresponding control point values.
Parameters are:
Rotation of the GPS coordinates around the project centroid.
Translation of the GPS coordinates in the N (+/-) and E (+/-).
Scale factor between GPS distances and control grid distances.

16. Rotation about project centroid 2 control points
Horizontal Rotation
Rotation about project centroid
2 control points
no redundancy
Horizontal rotation parameter is the horizontal rotation value that will cause the projected grid coordinates to best fit the control grid values.
Centroid computed using all H. control in the calibration.
GPS measured points are rotated about this centroid,
All measurements are rotated by the same amount.
Min. of 2 horizontal control points required to compute the rotation.
no redundancy for a check
error in 1 of the control points (or measured GPS coordinates) would not be detected.

17. Horizontal Translations
Points shifted (X,Y)
same amount
same direction
1 control point
no redundancy
Translations are computed as shifts (along the X,Y axis) that will cause the projected grid coordinates (from GPS) to best fit the control grid values.
All points are translated by the same amount.
Only 1 horizontal control point is required to compute the translation. However, this is the minimum requirement, and does not provide a check. Any error in the control point coordinate (or the measured GPS coordinate) would not be detected.

18. Horizontal Scale Factor
Ratio
GPS to grid distance
2 control points
no redundancy
Ratio of the true distance between control points (using the control grid coordinates) and the measured distances between the same control points (using projected grid coordinates from GPS).
All of the measured coordinates are scaled by the same amount.
Min of 2 horizontal control points are required.
No redundancy.
Any error in 1 of the control points (or measured GPS coordinates) would not be detected.

19. Residual Horizontal Residuals Redundancy = residuals Residual
GPS vs. control coordinate
3 control points
minimum
3 control points required for redundancy in the calibration.
If 3 (or more) horizontal control points are used
residuals are computed for each control point.
All GPS coordinates are adjusted (translated, rotated, scaled) by the parameter values determined in the calibration.
Adjusted grid coordinates (from the GPS measurements) are compared with the control grid values for all of the control points held in the calibration. The residual is the difference between the adjusted GPS coordinates and the control grid values.
Horizontal residuals should be relatively small
used to determine the quality of the least squares fit

20. Geoid model (optional)
Vertical Adjustment
Least squares best fit
WGS84 heights
Elevations
Parameters
Vertical shift
Vertical tilts (N & E)
Geoid model (optional)
Measured WGS84 heights compared with benchmark elevations.
Least squares best fit. Parameters are:
Constant (vertical shift) for all points
2. Vertical tilts (slopes N and E) of the inclined plane
If Geoid used - undulations are applied prior to computing the vertical adjustment.
If NO Geoid – then undulations are resolved as part of the vertical adjustment.
Simple planar Geoid model for the project area.

21. Geoid Model (Optional)
Earth’s Surface
Geoid N
WGS84 Ellipsoid
This diagram illustrates the relationship between the WGS84 ellipsoid, the Geoid, and the surface of the earth.
(N) - the modeled separation between the Geoid surface and the WGS84 ellipsoid.
Geoid surface represents the vertical datum to which orthometric heights, or elevations, are referenced.
Converts WGS-84 ellipsoid heights to Orthometric heights
- relative to a vertical datum.
specific Geoid model depends on the location of survey.
The Geoid model is optional in the site calibration, and may be used to model the undulations in the local Geoid, prior to computing the vertical adjustment.
Geoid separation (N)

22. Adjustment – No Geoid Model
3 control points
minimum
Earth’s Surface
WGS-84 Ellipsoid N NP
Geoid
Inclined Plane
For the vertical adjustment:
3 fixed control points uniquely define an inclined plane,
4 fixed control points define an inclined plane with redundancy
residuals not computed if less than 4 vertical control pts.
If NO Geoid model:
Software compares control point elevations against the measured WGS-84 ellipsoid heights
Computes approximate Geoid separations (N) at each control point held in the vertical adjustment.
Then computes a least squares best fit to create an inclined plane to approximate the local Geoid.
Inclined plane is used to compute Geoid separations (Np)
These are applied to all other measured WGS-84 heights.
Best fit inclined plane
approximates local Geoid

23. Residuals – No Geoid Model
Residuals at all vertical control
Earth’s Surface H e h N
Inclined Plane
Ellipsoid
Geoid
Residual NP
Residuals are computed at all of the control points (benchmarks) held in the vertical adjustment.
At each calibration point, the Geoid separation (N) is compared against the separation value (NP)
Remember that:
(N) is derived by subtracting WGS84 heights from the control point elevations.
(NP) is derived from the inclined plane.
The difference between these two Geoid separation values is the residual for that calibration point.
As explained in the previous slide, residuals are only computed if 4, or more, vertical control points are used in the calibration.
4 benchmarks minimum

24. Adjustment - with Geoid Model
Geoid model (Nm)
approximates Geoid
Earth’s Surface h
Ellipsoid H N
Geoid
Geoid Model Nm
Geoid values (N)
computed from benchmark elevations
(h – H) = N
Geoid model is used to model the separations between the WGS84 ellipsoid and the Geoid, or sea level datum.
However, the Geoid model may not accurately describe the true Geoid undulation in the local project area.
There may still be small differences between the modeled Geoid, and the Geoid shape described by the vertical control points.
For each vertical control point in the site calibration, the observed WGS-84 height (h) and the benchmark elevation (H) can be used to compute a value for the Geoid separation (N).
N = computed geoid height
Nm = modeled geoid height

25. Modeling Errors – Geoid Model
Earth’s Surface H e h N
Geoid Model
Ellipsoid
Geoid Nm NM DN
N - Nm
ΔN at each control point
The calculated Geoid separation value (N) can be compared with the separation value (Nm) - obtained from the Geoid model.
This comparison provides a ΔN value for each vertical control point used in the calibration.

26. Inclined Plane – Geoid Model
Ellipsoid
Geoid Nm
Inclined plane through ΔN
Inclined Plane DN + -
Residual
Lets take a look at how these delta N values are used to compute corrections to the original geoid model.
As illustrated in the graph at the bottom of the page
an inclined plane is fit through the delta N values at each of the vertical calibration control points. This inclined plane is computed as a least squares best fit.
The difference between the inclined plane and the ΔN value, for each vertical calibration control point, is the residual for that control point.
The inclined plane provides geoid model correction values that can be used to correct the original geoid model separations for all other measured points in the project.
Corrections to Geoid model

27. Geoid Model - Benefits
Improved modeling results when working with a larger calibrated site that incorporates a high degree of geoid undulation
Performing a site calibration along the front range of Colorado

28. Calibration Results - Applied
Computed using control points
Applied to all points
As described earlier, the calibration parameters are computed by comparing GPS derived coordinates with the corresponding control grid values for all of the control points held fixed in the calibration.
While the calibration is computed using only the control points held fixed in the calibration, the calibration results are applied to all of the points in the project file.

29. Section 3 – Control Requirements
Horizontal control requirements
Vertical control requirements
Recommendations
This section of the course will provide a brief description of the control point requirements for a successful site calibration.
we will discuss both horizontal and vertical control requirements, and
provide recommendations for the placement of control on different job sites.

30. Control Requirements Minimum redundancy Trimble recommends
3 Horizontal
4 Vertical
Trimble recommends
5 Horizontal
5 Vertical
More is better!
Basic rules regarding control requirements:
The minimum requirements to achieve redundancy are:
3 Horizontal and 4 Vertical control points
No redundancy means no residuals - no check on your control.
Errors in the control coordinates will not be apparent.
Errors in GPS measurements on the control will not be apparent.
Trimble recommends:
5 Horizontal and 5 Vertical control points
Trimble software allows up to 20 control points in the site calibration.

31. Control Placement Critical to success Cover entire project
Project Area
Critical to success
Cover entire project
Control placement is critical to success of the GPS site calibration.
Must be spaced to cover the entire project area.
This applies to both horizontal and vertical control points.

32. Control Placement Stay inside control Vertical tilts
Vertical tilts magnified
Limits of control
No Survey Here
Stay inside control
especially vertical
Vertical tilts
magnified outside control
Never work outside your control limits
Especially critical for vertical control
Error in the vertical tilt (of the inclined plane) will be magnified outside of the control area

33. Horizontal and Vertical Control
H & V
may be different
You decide: H V 3D
It is important to follow the minimum recommendations for control.
However, the horizontal and vertical control do not have to be the same control points.
You determine how a control point is used in the calibration.
You may select a control point to be:
Turned off in the calibration,
Used as vertical control only,
Used as horizontal control only, or
Used as both horizontal and vertical control.

34. Horizontal and Vertical Control
Mix and match
as required
▲= Horizontal
■ = Vertical
You can mix and match how control is used, as long as the recommended numbers of both horizontal and vertical control points are met.
The diagram shows a mixture of control types, where
the black triangle signifies a horizontal control point,
the grey square signifies a vertical control point.
Notice that some of the points are shown as both horizontal and vertical control.

35. Limit calibration size
Site Recommendations
Limit calibration size
minimize scale distortion
Practical limitation
10 km x 10 km
10 km
To minimize scale distortions, the calibration area should be limited in size.
A practical size limitation is approximately 10 kilometers by 10 kilometers (6 miles by 6 miles).

36. Site Recommendations Multiple zones Overlap long linear projects
common control
Calibration 2
Calibration 1
Overlap area
For large projects - consider splitting the project into several calibration zones.
This is a practical solution for long linear sites – such as road construction projects.
Overlap the calibration boundaries so that either calibration may be used when working near the edge where the calibration areas are joined.
Control points that fall within the overlap area should be used in both calibrations.

37. Site Recommendations Large ΔH Split into zones Minimize ΔH
scale errors
Split into zones
Minimize ΔH ΔH
Calibration 2
Calibration 1
Trimble software requires that we supply an average project height - to be used in the horizontal adjustment.
However, large variations in elevation, across the project area, will cause problems with the horizontal scale.
The calibration will compute 1 horizontal scale factor for the average elevation of the project, and points at the higher or lower elevation limits will see some scale distortion.
For projects with large variations in elevation - consider splitting the project into several calibration zones.
Each calibration should be computed at the average elevation of that zone.
Design each calibration zone to minimize elevation change across the zone.

38. Section 4 – Interpreting Results
Residuals
Horizontal adjustment parameters
Vertical adjustment parameters
At this point, we should discuss guidelines for interpreting the results of the GPS site calibration.
Topics will include:
the significance of the calibration residuals, both Horizontal and Vertical, and
the parameters computed in the horizontal and vertical adjustments.

39. Interpreting Results - Residuals
H and V
Large residuals
Control or measurement error
Pay close attention to the residuals for each control point.
Check both the horizontal and vertical residuals.
If you do NOT see residuals, for either the horizontal or vertical adjustment, this indicates there was not enough control for redundancy.
Large residual values indicate a problem with the calibration:
errors in the control coordinates, or
errors in the GPS measurements on the control points in question.
If a control point gives good residuals in Horizontal, but large residuals in vertical - it is acceptable to re-compute the calibration holding that control point in horizontal only.
Same for the reverse situation.
Note that in the example…several of the control points are held fixed in only the horizontal or vertical component.

40. Horizontal Adjustment Parameters
Scale factor
close to 1
Rotation
match local orientation
Max. H. Residual
Horizontal adjustment parameters from site calibration in Survey Controller software.
In this example, the horizontal scale factor is very close to 1.
Indicates that scale of the projected grid coordinates closely matched the scale of the control grid values.
The horizontal rotation is the amount of angular rotation, from geodetic North, required to match the orientation of the local grid coordinate system.
This example shown in arc seconds - indicates that the local grid orientation is just slightly different from geodetic North.
The maximum horizontal residual indicates the amount of horizontal adjustment required on the worst fitting control point.
This is the largest difference between a control grid coordinate and the adjusted GPS observation on that point.

41. Vertical Adjustment Parameters
Slope N & E
vertical tilts
Constant Adjustment
vertical shift
all points
Max. V Residual
The vertical adjustment computes a best fit inclined plane between the measured GPS heights and the local control elevations.
Slopes N & E are the vertical tilts required for the inclined plane to match the vertical control.
The Constant adjustment is the constant vertical shift applied to all points in the calibration.
If NO Geoid model is used – value will be approximately equal to the size of the Geoid separation in the local area.
The maximum Vertical residual indicates the amount of vertical adjustment required on the worst fitting control point.

42. Section 5 – Calibration Scenarios
Defined coordinate system
(US state plane zone)
Arbitrary grid system
(local ground coordinates)
1 point calibration
(scenarios for H & V adjustment)
In this section we will discuss several different calibration scenarios, and explain the calibration settings, in Trimble Survey Controller software, for each type of calibration. The following calibration scenarios will be discussed:
Calibration to control points in a pre-defined grid coordinate system. For example: - US State Plane grid coordinates, New Zealand Map Grid coordinates, UTM coordinates, etc.
Calibration to control points in an arbitrary, assumed, local grid system. For example: - local grid coordinates from an optical traverse, with assumed starting coordinates and azimuth.

43. Calibrating to Pre-defined Grid
Select from library
“GRID” coordinates
Project height
ellipsoid
This screen shows the calibration settings in Trimble Survey Controller software.
When calibrating to a pre-defined grid coordinate system:
the datum transformation, reference ellipsoid, and map projection parameters are already defined.
in most instances these parameters will also be available in the coordinate system library..
Since we are calibrating to a true grid coordinate system:
the calibration settings (in the project settings dialog) should be set to “grid” coordinates, as shown.

44. Calibrating to Pre-defined Grid
Projected to mapping plane
Position at ground surface
Mapping Plane at Ellipsoid A B
Projected Grid
Coordinate
Horizontal adjustment
scale ~ 1
small rotation
WGS-84
Coordinate
SF ≈
The WGS-84 coordinates are projected to grid using the pre-defined coordinate system parameters.
The mapping plane will be located at the reference ellipsoid.
Horizontal and Vertical adjustments are performed between the projected grid coordinates and the control grid values.
Horizontal adjustment results should show:
scale factor very close to 1
the closer to 1 – the better the GPS measurements fit the control values
a very small rotation value
since the orientation of the local grid control is defined in the map projection.
OF ELLIPSOID
TO CENTER

45. Calibrating to Assumed Grid
“no projection / no datum”
“Ground” coordinates
Project height
Geoid model
if available
This screen illustrates the settings for calibration to an assumed grid coordinate system.
When calibrating to an assumed local grid system
the datum is assumed to be WGS-84, and
the map projection parameters are not defined.
In this case the software creates a local (default) Transverse Mercator projection – at the WGS-84 ellipsoid - in the project area.
This local grid coordinate system is most likely also a “ground” coordinates system. In this case,
the calibration settings should be set to “ground”
the average project ellipsoid height should be entered.
You may also choose the appropriate Geoid model – if available.

46. Calibrating to Assumed Grid
Projected to map grid
Grid scaled to ground
Control at ground
Project height
Scaled to project height
SF > A B
Projected to grid
SF ≈
WGS84
Horizontal adjustment
scale ~ 1
rotation – any value
depends on local orientation
In this example, we are calibrating to an assumed grid coordinate system at high elevation (Denver, Colorado).
Since we selected “no projection / no datum” in the coordinate system settings,
the datum is assumed to be WGS-84 – no datum transformation
WGS-84 coordinates are projected to TM at project location.
We are calibrating to a coordinate system at ground (at high elevation).
projected grid coordinates will be scaled to ground, at the average height of the project, prior to computing the Horizontal adjustment.
Horizontal adjustment is performed between:
projected (and scaled) grid coordinates (at ground)
local control values at ground.
Results should be:
scale factor close to 1 – height scale applied inside the map projection.
rotation may be any value – since local grid has assumed orientation.
OF ELLIPSOID
TO CENTER

47. 1 Point Calibration to Ground
“no projection / no datum”
“Ground” coordinates
Project height
Geoid model
if available
This screen illustrates the settings for calibration to an assumed grid coordinate system.
When calibrating to an assumed local grid system
the datum is assumed to be WGS-84, and
the map projection parameters are not defined.
In this case the software creates a local (default) Transverse Mercator projection – at the WGS-84 ellipsoid - in the project area.
This local grid coordinate system is most likely also a “ground” coordinates system. In this case,
the calibration settings should be set to “ground”
the average project ellipsoid height should be entered.
You may also choose the appropriate Geoid model – if available.

48. 1 Point Calibration to Ground
Projected to map grid
Grid scaled to ground
SF >
Scaled to Project Height
Project Height A B
Projected to Grid
WGS84
SF =
Horizontal adjustment
scale = 1
no rotation
geodetic North
We are using a 1 point calibration to scale measured points to ground.
the control coordinate can be any arbitrary value.
project height must be accurate.
Since we selected “no projection / no datum” in the coordinate system settings,
the datum is assumed to be WGS-84 – no datum transformation
WGS-84 coordinates are projected to TM at project location.
Projected grid coordinates will be scaled to ground, at the average height of the project, prior to computing the Horizontal adjustment.
Horizontal adjustment computes shifts in X,Y only. No scale or rotation since only 1 control point.
Results should be:
scale factor = 1 – height scale applied inside the map projection.
no rotation – orientation is geodetic north from GPS.
OF ELLIPSOID
TO CENTER

49. 1 Point Vertical Calibration
With geoid model
maintains shape of Geoid
vertical shift
no vertical tilts
Earth’s Surface
WGS-84 Ellipsoid h H N
We already know that calibrating to 3 (or more) benchmarks provides a best fit inclined plane that:
approximates the local Geoid, or
provides corrections to the Geoid model, depending on the circumstances.
In constrast, calibrating to just 1 vertical control point (with a Geoid model) will maintain the shape of the Geoid model…resulting in a constant vertical shift only. No vertical tilts are computed.
NOTE: This is useful when you have less than optimal vertical control…i.e. 1, 2, or 3 benchmarks – no redundancy.
This adjustment relies on 1 control point to derive vertical shifts.
If you have second (or third) benchmark…these are used as checks.
Geoid
Geoid Model

50. Summary GPS site calibration Computes transformation parameters
WGS84 to grid
Grid to WGS84
To summarize:
The GPS site calibration is required to compute transformation parameters between WGS84 and grid coordinates.
This is a 2 way street, and calibration parameters can be applied to move back and forth between the coordinate types.

51. Calibration requires a coordinate system
Summary
Calibration requires a coordinate system
Datum transformation
WGS84 to local ellipsoid
Map projection
Ellipsoid to map grid
Use published – if available
We have also seen that the site calibration requires an underlying coordinate system. This is because we cannot directly compare geodetic coordinates with grid coordinates.
The coordinate system is required to provide:
Datum transformation from WGS84 to local ellipsoid
Map projection from ellipsoid to local grid
If published parameters are known – then use them.

52. Elements of the calibration
Summary
Elements of the calibration
Horizontal adjustment
Rotation, translations (2), scale
Vertical adjustment
Vertical shift, tilts (2)
Geoid model - optional
We also know that the calibration consists of several elements:
The horizontal adjustment between projected “grid” (N & E), and control grid (N,E)
This produces horizontal rotation, 2 translations, and horizontal scale.
The vertical adjustment between ellipsoid height, and the control elevations.
This produces a vertical shift, and 2 tilts.
The geoid model is optional.

53. Control requirements: For redundancy (residuals)
Summary
Control requirements:
For redundancy (residuals)
3 Horizontal
4 Vertical
Trimble recommends:
5 Horizontal and Vertical
We talked about the control requirements for a successful site calibration.
For redundancy (residuals) we need:
3 horizontal control points
4 vertical control points
Trimble recommends you use 5 or more (H & V)

54. Summary Site recommendations Stay inside control
Limit calibration size
Multiple calibrations for:
Long linear projects
Large elevation range
We also talked about specific site recommendations.
Stay inside the limits of your calibration, as defined by the control that you used.
Limit the size of the calibration – to control scale distortion
Use multiple calibrations for:
Long linear projects, and
Projects with large elevation range

55. Interpreting calibration results
Summary
Interpreting calibration results
Pay attention to residuals
Horizontal
Scale and rotation
Vertical
Tilts and vertical shift
When interpreting your calibration results:
Pay attention to the size of the residuals (H&V)
Understand the significance of the other parameters:
Horizontal scale and rotation
Vertical tilts, and the vertical shift

56. Calibration scenarios
Summary
Calibration scenarios
Defined grid
Use the projection and parameters
Arbitrary grid
No projection / no datum
1 point calibration
Horizontal
Vertical
We also discussed several different scenarios for the site calibration.
If calibrating to a defined grid coordinate system, always use the published projection parameters.
If calibrating to an arbitrary (local) grid system, use the “no projection/no datum” option. This just means that we are not specifying the parameters. The software will create a default TM projection.
Also, be aware of the possibilities of using a 1 point calibration for either the H or V.

57. Questions?
We also discussed several different scenarios for the site calibration.
If calibrating to a defined grid coordinate system, always use the published projection parameters.
If calibrating to an arbitrary (local) grid system, use the “no projection/no datum” option. This just means that we are not specifying the parameters. The software will create a default TM projection.
Also, be aware of the possibilities of using a 1 point calibration for either the H or V.