Use the Model Selected option menu to select the type of model. The Actual Model field provides feedback on the actual model that can be calculated from currently captured control points.

The control points used to control the building of a model are displayed below the menu bar of the dialog box and the Model Selection area.

This information provides feedback to assist you in the building of a model with control points. It includes nine columns, which contain the number of a control point, its on/off status, its X and Y coordinates in the base and uncorrected system, and its residuals relative to the actual model.

The Helmert model, also called “rigid body,” performs a rotation and two translations (X and Y); however, no scaling is done. This model guarantees that the uncorrected data retains its proportions since the image or design elements are only moved and rotated.

The Similitude model performs a rotation, two translations (X and Y), and a scaling that has the same factor for the x- and y-axis. You can use a Similitude model to cut an image, to rotate an image, or to register two images with the same deformation relative to each other.

The Affine-1 performs a rotation, two translations (X and Y), and applies a different scale factor for the x-, y-axis as well as a factor that changes the orthogonality of these axes. You can use the Affine-1 model to register a document that has very little deformation such as a scanned map.

The Projective model projects one plane into another plane. Like the Similitude and the Polynomial-1 models, it can be used to register a document that has very little deformation. For example, you can use it to register an aerial photograph that has little relief.

The Thin Plate Spline model is based on a four variable mathematical algebraic formula. This means that this model requires at least four pair of control points to resolve the transformation model.

The benefits of this model resides in the fact that in order to compensate for the distortion caused by the rubbersheeting, instead of moving the control points to accommodate the residual values as in the traditional models, the Thin Plate Spline does not move the control points but instead, applies a correction elsewhere around the control points.

The trade-off is where it will most often be required to enter more control points than a traditional model. Control points will be positioned where the two systems (correct and uncorrected) do not aligned. Control points must be entered until the tanglement is satisfactory.

The Polynomial-2 and 3 models are used to register documents that have moderate relief. However, they are not suitable for documents that contain accentuated relief. For example, you can use these models to register aerial photographs of a city with low hills, but should not use these models to register aerial photographs of a mountainous region.

When there are not enough points to build the requested model, a provisional model, needing less points, is calculated to support the dynamic warping.

When the minimum number of points is reached for the model requested, the Actual Model field displays the same name as the Selected Model option menu. If Dynamic Warping in Views Displaying Uncorrected Data is on and for any reason the model cannot be calculated with the present set of control points, the actual model shown is None.

The Control Point # column provides a sequential number for all control points entered. If a point is removed or if a new point is inserted between two existing points, the list renumbers.

The On column indicates whether the corresponding control point is on or off in the calculation of the actual model. An "X" indicates on. An empty space indicates that this point is turned off. Double-clicking a line of the list toggles the status of the corresponding control point between on and off.

The X and Y columns under Base System display the coordinates of control points in the “base” system of coordinates. This system is the one into which the image is to be transformed after it is resampled by applying the model.

The X and Y columns under Uncorrected System display the coordinates of control points in the “uncorrected” system of coordinates. The residual of a control point is the difference in location between the position where a control point is pinned on the uncorrected system as compared to the position where it should be according to the actual model. When a model is built with the minimum number of control points, such as four points for the Projective, there is no residual (except for Helmert). This situation means that the model “trusts” you and puts the calculated point exactly where you pinned it on the uncorrected system.

In fact, since the model has only the minimum number of points, it must make this assumption. As soon as an extra point is provided, it can compare the position you “guessed” with the position it calculates through the model. The difference between your “guess” and the calculated position is the residual.

After a model is updated, the distance between the two corresponding marks reveals the residual for this pair of control points. As long as there is not an extra point, the model is exact, i.e., there is no residual (except for Helmert). Consequently, the two corresponding marks of each pair coincide.

The model supported is always the best fit to all points, when extra points are provided. Normally, when a control point is inconsistent with the others, its residual is greater. The residuals displayed in the Control Points List box are indications of points that can need adjustment. Turning off the point with the greatest residual normally improves the actual model.

Residuals are distances. The three columns X, Y, and XY under Residuals indicate the X component, the Y component, and the magnitude (XY) of this distance.

The Helmert model differs from the other models in respect to residuals. Because this model guarantees that the body of the uncorrected geometry stays rigid (without scale modification), the minimum number of control points usually generates residuals. In fact, with two control point pairs, the Helmert model moves and rotates the rigid body until the residuals are minimized.

Used to specify whether the calculated and displayed residual values apply to the Base System or to the Uncorrected System.

The On/Total field displays the number of control points turned on over the total number of control points in the present list.

This field displays the standard deviation or root mean square error for each set of residuals, one for each of the X, Y, and XY columns.

The standard deviation values provide a good assessment of the model, and supplement the individual residuals.

The Root Mean Square (RMS) error gives an estimate of the overall error for the entire collection of active control points (where N is the number of control points):

RMS for X = square root (sum(square(residual X))/N)

RMS for Y = square root (sum(square(residual Y))/N)

RMS for XY = square root ((square(residual for X)) + (square(residual for Y))

The File menu provides access to all necessary options to manage Register files (New, Attach, Import, Save, Save As). A Register file is used to save a transformation model for later use.

It is now possible to save a register list of control points into a text file. To do so:

1. Open an existing RGR file or create one.

2. From the Register dialog box, select File>Save As.

   The Save Model dialog box opens.

3. In the Select Format To Save option menu, select “Text (Comma delimited) [*.txt]”

4. Enter a file name and a location folder.

5. Click OK

The resulting file can be opened in a text editor or imported in a spreadsheet application supporting Comma Delimited file formats.

It is now possible to import *.COR files from Bentley I/RAS B using the File > Import menu.

The Edit menu provides access to various tools and dialog boxes that are used to create or modify a model. Use these features to enter, modify, delete, highlight, or locate pairs of control points.

Choose Add Control Points from the Edit menu to manually enter a pair of control points: (Base X, Base Y) and (Uncorrected X, Uncorrected Y).

The On/Off check button toggles this pair of points between on or off. When on, the pair of points is taken into account for the calculation of the actual model and the corresponding marks display in the appropriate views. When off, this pair is suppressed and the marks are not shown. The points, however, can be turned on and used again by using the Modify Control Points dialog box.

The new pair of points is always added after the previously selected line. If the new line is inserted before the last existing line, a renumbering of the following lines results.

In some situations, this result might not be desirable. Consider when an analog hard copy map is used as the base data. In this case, the corresponding numbers would be written directly on the map. Any changes in the sequence of the numbers requires a renumbering of the points on the hard copy. To avoid renumbering in such cases, add points to the end of the list.

If you wish to toggle points on or off, double-click on the corresponding line.

Choose Modify Control Points to modify the selected pair of control points by manually editing the following coordinates: (Base X, Base Y) and (Uncorrected X, Uncorrected Y).

The On/Off check button toggles this pair of points between on or off. When on, a pair is taken into account for the calculation of the actual model and the corresponding marks display in the appropriate views. When off, this pair of points is suppressed and the marks are not displayed. Alternatively, double-click on the corresponding line to toggle points on or off.

Choose Delete Control Points to remove the selected pair of control points from the list.

Choose Highlight Control Points to highlight the selected pair of control points. This feature uses the same color that MicroStation uses for highlighting elements when they are selected or identified.

Choose Locate Control Points to locate and highlight the selected pair of control points in the center of views that are set for locating control points (See “View > Views Used to Locate Control Points”). This feature is useful for rapidly panning to the location of control points that are not visible. The highlighting is done with the same color that MicroStation uses for selecting elements.

The View menu provides access to two toggles. One toggle controls the dynamic warping mechanism and the other, the display of control points. Dialog boxes are also provided to let you select the views which will display the dynamic warping of vector on uncorrected data and to select the views which will display the location of control points. A final dialog is used to set the warping window.

Dynamic Warping in Views Displaying Uncorrected Data permits you to control the dynamic warping mechanism inside each view where uncorrected data is displayed.

If on, it activates both the dynamic warping mechanism and the updating of the model. Each time that a pair of control points is entered or modified, the model is updated and the base vector data is warped. Base vector data is redrawn in views where uncorrected data is displayed, as an overlay to the uncorrected image(s) or vector(s), after being geometrically transformed through the actual model.

If on and the model cannot be calculated with the present set of control points, the actual model displayed will be None and the dynamic warping will not be activated.

Turn off to inhibit both the dynamic warping mechanism and the updating of the model; then, the Actual Model shown will be None.

The dynamic warping process can take time to complete. If you wish to abort it, press the <Esc> key. It is recommended that you use a small set of base vector data in order to accelerate the dynamic warping process. If using a small set of base vector data is not practical, set the warping window so that only the design elements inside the area that you wish to register are warped.

You can also control the warping process for each supported design element type.

Panning in a view displaying uncorrected data is not recommended when dynamic warping is on. The warping of vectors takes some time and in some circumstances causes MicroStation to not trap the release of the data point button. When this happens, the panning does not stop and performance is seriously degraded. To prevent this situation, move the mouse to another window and click the Reset button (or press the <Esc> key and immediately click the Data button) several times until the panning ceases.

Choose Views Displaying Uncorrected Data to identify the view or views where the uncorrected data (the images or vectors to be corrected) will be displayed. If Dynamic Warping in Views Displaying Uncorrected Data is on, the base vector data will be warped over the uncorrected data in the specified views. It will be redrawn after being geometrically transformed through the actual model. In all other views, vector data will behave normally. The check button Also Display Non-Warped Elements controls the presence or absence of non-warped elements (i.e., the original design elements without transformation) in uncorrected views

Choose Views Used to Locate Control Points to identify the view or views where the Locate Control Points feature will be activated (See “Edit > Locate Control Points”).

When the Auto Locate on Base Control Point Pinning toggle is on, the selected views will be automatically zoomed around a base control point just after it is pinned.

Use this feature when you want to refine the pinning of control points after you have done it approximately in a view with a smaller scale.

For example, use View 1 for a synoptic display of the whole image. Use View 2 as the detailed view where a zoom occurs automatically after a base control point is selected. Then, View 2 should be selected in the Views Used To Locate Control Points dialog box.

Here is a typical procedure you can follow as an example.

To use a synoptic view and a detailed view when pinning control points

1. Turn on View 2 in the Views Used To Locate Control Points dialog box.

2. Turn on the Auto Locate on Base Control Point Pinning toggle.

3. Select the Place Control Points tool from the Register toolbox.

4. Pin a base control point in View 1. View 2 automatically zooms around this point.

5. If the pinning of this point needs refinement, press the Reset button. That removes the last base control point and allows you to pin it again (in the zoomed view).

6. Pin the uncorrected control point and iterate the process from step 4.

Choose Warping Window to set the size of the warping window. The warping window is the extent in which the dynamic warping occurs if Dynamic Warping in Views Displaying Uncorrected Data from the View menu is on. You should set the size of the warping window if the extent of the design elements is larger than the area that you wish to register. If you choose this option, the time to warp the design elements is reduced since registration does not consider the elements outside of the warping window.

Show Control Points permits you to control the display of control point marks.

If on, activates the display of the control points mechanism. Then, both control points for all pairs of points are displayed according to the selected colors.

If off, suppresses the display of the control points mechanism.

Use Register/Settings to set the colors of the symbols that are used to mark the control points, to toggle on or off the Warning When Renumbering option, or to access the Elements Transformation dialog box.

Choose Colors for Control Points to set the colors for the symbols that are used to mark control points. Colors for the base control points mark and the uncorrected control points mark can be set independently. Next to each field where the color number is entered, the actual color corresponding to this number displays on a color button. You can also select the color with the color picker that pops up when you click the color button.

Warning when Renumbering permits you to be warned when the list of control points is going to be renumbered. If a line is inserted or deleted before the last existing line in the control points list box, a renumbering of the next points results.

If on, you are warned when a renumbering is about to occur.

If off, you are not warned when a renumbering is about to occur.

Choose Elements Transformation to control which design element types are used for the dynamic warping process, the Copy Vectors command, and the Move Vectors command. To disable a specific design element type for the transformation process, select the None option for the appropriate option button.

To enable a specific design element type, select the appropriate option for each design element type:

• All Coordinates

• Origin Only

• Stroking & All Coordinates

When All Coordinates is selected, the transformation model is applied to each (X,Y) coordinate of the element.

When Origin Only is selected, the transformation model is applied only on the origin of the element. Others characteristics such as rotation angle, scale, and so forth are not modified.

When Stroking & All Coordinates is selected, the transformation process modifies the original structure (i.e., center point, start angle, etc.) of the element. First, the element is stroked into a complex chain based on the specified Tolerance. Second, the transformation model is applied to each (X,Y) coordinate of the element. If the element does not transform as expected, adjust the Tolerance and repeat the process.

The Apply menu provides access to the To Image menu item, which opens the Resampling dialog box.

Selecting To Image from the Apply menu opens the Resampling dialog box. Use the Resampling dialog box to set all parameters to resample an image through a geometric correction model built with Register.