Transform Survey Points

Transform survey points by moving, rotating, and/or scaling them using either of the following methods:

Transform survey points using points pairs - This is the most popular method for performing a point transformation and typically provides excellent results. You simply specify the point pairs you want to use for the transformation. You can then select to have Trimble Business Center automatically disable outlier point pairs and determine the best calculation method and transformation parameters to use to achieve minimal overall point pair residuals. If necessary, you can override any automatic settings to obtain more optimal results by ensuring the more trusted point pairs have lower residuals than less trusted point pairs.
Transform survey points without using point pairs - This method for performing a point transformation does not require the use of point pairs. Instead you manually specify the parameters to use for the transformation.

Prerequisites:

None.

To access the command:

Select Transform Survey Points in Survey > COGO.

To transform survey points using point pairs:

In the Transform Survey Points command pane, click in the Objects to transform field. Then, using a graphic view, Project Explorer, or Points Spreadsheet, select the points you want to transform. Or, click the Options button for additional selection options.
In the Calculation Method box, select the method you want to use to calculate the transformation: Helmert or Least squares.
The goal of computing scale, translation, and rotation parameters is to minimize the residuals, or error, between the transformed “from” points and the “to” points. The Helmert method essentially defines horizontal residual as being separate and independent from vertical residual, whereas the least squares method defines the residual to be the RMS value of all residuals. Because the two methods are essentially minimizing different things, they produce slightly different results. For 5-parameter transformations, this difference is hardly noticeable, but for 7-parameter transformations, it is more noticeable. Therefore, if you are not fixing the vertical scale to 1.00 (see below) and your data is a mixture of 2D and 3D, it is recommended that you select Helmert. Otherwise, select Least squares.
In the Scale/Rotation Origin box, select either of the following options:
- Centroid - Scale or rotate around an origin point that is defined by the mean or average position of all of the selected points.
- First "From point" - Scale or rotate around the "from point" in your first point pair selection (see step 4).
Using the fields in the Transform Calculator box located in the lower portion of the pane, define the point pairs you want to use to calculate the transformation.
Note: Consider adding your most trusted point pairs first so they display together at the top of the list, making their residuals more convenient to view.
1. Click in the first From point / to point field and then either type in or select in the Plan View the first "from" point you want to transform.
  If you made your selection in the Plan View, your cursor automatically moves to the second From point / to point field. Otherwise, click in the second field.
2. Type in or select in the Plan View a "to" point or location to which you want to move the "from" point.
3. Repeat to add two or more additional point pairs.
  As you add point pairs, the Transformation Parameters fields are updated automatically as the data is recalculated to provide optimal results. After you specify the third point pair, residuals display for all point pairs and are constantly updated as you enter each new point pair (or make any changes to parameters).
  A minimum of three point pairs is required to activate the Automatically determine best settings button. However, the button can only identify outliers in the point pairs if there are more point pairs than the minimum. Therefore, four or more point pairs are recommended if you plan to use the button.
  Point pairs can be 2D or 3D. Note that some point pairs may be ignored in the transformation calculation. For example, a 7-parameter transformation cannot use 2D points.
When you are done specifying point pairs, optionally click the Automatically determine best settings button located at the top of the Transform Survey Points command pane.
An Information message displays indicating any changes that were automatically made to the Calculation Method and/or Transformation Parameters check boxes to optimize the transformation and provide the lowest overall point pair residuals. The message also identifies any outlier point pairs that were automatically disabled. Review the point pair residuals to determine if they are acceptable.
Note: The software defines an outlier point pair as any point pair whose residual value exceeds three times the median for all of the residuals. If a "trusted" point pair was identified as an outlier and disabled, you can select the check box to re-enable it, but note that it will impact the residuals for the other point pairs.
Click OK in the Information message window.
If you do not think the automatic settings provide optimal results (that is, lowest residuals on the most trusted point pairs), you can make changes manually to see if you can achieve better results.
Optionally, change the Calculation Method, select or deselect any of the Transformation Parameters, and/or select to enable or disable any point pairs to see if you can obtain more desirable results.
For additional instructions, see steps 4 and 5 in the next section, "To transform survey points without using point pairs."
When you are satisfied with the point pair residuals, click the Apply button to transform the selected points using the specified parameters.
The selected points are transformed and a message is displayed prompting you to view the Transform Survey Points Report, which includes complete transformation information. Note that the report is not saved into the project so this is the only chance to view it.
After performing a transformation:
- Any global or local coordinates for the transformed points are disabled.
- Any surveying observations flowing into or out of each transformed point are disabled. This includes azimuths, total station observations, RTK and post processed vectors, photogrammetry observations, and anything else the software uses to compute a survey.
  Note: Depending on the survey, there is an alternative to disabling coordinates and observations during a transformation. Most surveys originate from a few control points. These are points from which the other points are calculated. By transforming these points, the other points will follow. Therefore, you can transform just the control points, record their new coordinates, undo the transformation (Ctrl + Z), enter the new coordinates for the control points, and recompute the project. All of the points "flowing" from the control points will be transformed accordingly and no coordinates or observations are disabled.

To transform survey points without using point pairs:

At the top of the Transform Survey Points command pane, optionally select the appropriate preset button to preconfigure the default settings for the Transformation Parameters group box:
- 5-parameter preset - A 5-parameter transformation includes translation, Z rotation, horizontal scale, and fixed vertical scale. Therefore, the X Rotation and Y Rotation transformation check boxes are deselected, and the Fix Vertical Scale at 1.00 and Horizontal Scale check boxes are selected.
- 7-parameter preset - A 7-parameter transformation includes translation, full 3D rotation, and symmetrical scale. Therefore, the X Rotation and Y Rotation transformation check boxes are selected, the Fix Vertical Scale at 1.00 check box is deselected, and the Horizontal Scale check box is changed to a Horizontal and Vertical Scale check box and is selected.
These buttons are simply an aid in determining which parameters to use based on the transformation type. Regardless of your selection, you can select or deselect any parameter as necessary in the following steps to obtain optimal results.
Click in the Objects to transform field. Then, using a graphic view, Project Explorer, or Points Spreadsheet, select the points you want to transform. Or, click the Options button for additional selection options.
In the Transformation parameters box, enter appropriate values for the checked parameters:
- Delta Easting and Delta Northing - Moves the points horizontally by the displayed distance value. Positive values move the selected objects to the East and North. Type in values or select a distance in the graphic view.
- Delta elevation - Moves the points vertically by the displayed distance value. A positive value moves the selected objects up.
- Rotation - Rotates the points around the X, Y, and Z axes accordingly by the displayed rotation values. A positive value rotates the selected objects clockwise. Note that selecting either the X Rotation or Y Rotation check box causes both check boxes, along with the Z Rotation check box, to be selected (the default configuration for a 7-parameter transformation). However, the Z Rotation check box can be selected without the X Rotation or Y Rotation check boxes being selected (the default configuration for a 5-parameter transformation).
- Scale - Scales the points by the displayed scale factor. You can either select the Fix Vertical scale at 1.00 check box and specify the Horizontal Scale (the default configuration for a 5-parameter transformation), or deselect the Fix Vertical scale at 1.00 check box and specify a single value for the Horizontal and Vertical Scale (the default configuration for a 7-parameter transformation).
In the Scale/Rotation Origin box, select either of the following options:
- Centroid - Scale or rotate around an origin point that is defined by the mean or average position of all of the selected points.
- First "From point" - Scale or rotate around the first point in your point selection in step 2. If you selected the points to transform individually using the Project Explorer or Points Spreadsheet, the first point you selected is the first "from" point. If you selected the points en masse in a graphic view by clicking and dragging a selection box, the lowest alpha/numeric point ID (the highest in the Project Explorer list) is the first "from" point.
Click Apply to transform the selected points using the specified parameters.
The selected points are transformed and a message is displayed prompting you to view the Transform Survey Report, which includes complete transformation information. Note that the report is not saved into the project so this is the only chance to view it.
After performing a transformation:
- Any global or local coordinates for the transformed points are disabled.
- Any surveying observations flowing into or out of each transformed point are disabled. This includes azimuths, total station observations, RTK and post processed vectors, photogrammetry observations, and anything else the software uses to compute a survey.