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Localization in MAGNET Field
When performing a task of transformation of GNSS points coordinates measured in WGS-84/Datum/Grid coordinate system into a Ground coordinate system, we cannot use the algorithms of transformation which are applied to predefined or created by the user grids and datums. In this case, MAGNET Field does not have predefined relation between two coordinate systems. We use Localization to perform coordinate transformation from WGS-84/Datum/Grid to Ground (and vice versa).
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Basic Concept of Localization
Localization in MAGNET Field is a calculation of transformation parameters between WGS84/Datum/Grid and a ground coordinate system. To perform localization, you need to have two independent sets of coordinates for the same point or few points in the MAGNET Field. An independent set of coordinates is a set of such point coordinates that do not have a relation between each other. To perform localization in MAGNET Field, you need to manually select coordinates in the Ground coordinate system ("Known Point") and in the Grid coordinate system or WGS84/Datum coordinate system ("Measured Point") for the same point in the current job. Such a point is called Localization Point.
In MAGNET Field, horizontal localization and vertical localization are performed separately.
- Horizontal localizations use two-dimensional conformal transformations. This kind of transformation is also known as a four-parameter similarity transformation (Rotation, Scale, and two translation parameters (DX, DY)). To relate the points’ geodesic coordinates (measured with GNSS receivers) to local plane coordinates (obtained with total stations, etc.), a map projection is used as an intermediate step.
- Vertical localizations use a three-parameter transformation (one shift (HO) and two slopes (Hx, Hy) to convert between the points’ ellipsoidal or orthometric heights and the elevations in the local height system. These three parameters are necessary in order to specify the plane that would adequately model the difference between the local geoid and the WGS84 ellipsoid in the given local area.
You determine how the localization points will use in localization parameters calculation by selecting the corresponding check boxes:
- Use Horizontal - the point will use only in horizontal plane localization.
- Use Vertical - the point will use only in vertical plane localization.
- Use Horizontal and Use Vertical - the point will use in both localizations.
Also you can select the point which will use only in the determination of rotation between two coordinate systems by selecting the corresponding check box Rotation Only.
When you check Use Horizontal and / or Use Vertical you can use one, two, three and more localization points. For this case MAGNET Field will calculate a different set of transformation parameters and residuals. The table displays which parameters are calculated in the process of localization, some parameters can be set to zero depending on the used number of the localization points:
Localization |
Parameters |
ONE Point |
TWO Points |
THREE Points |
FOUR Points |
Horizontal Plane
|
Note: To perform localization in horizontal plane, check the Use Horizontal box for minimum ONE point. |
DX, DY - horizontal offset between two coordinate systems |
CALC |
CALC |
CALC |
CALC |
Scale - combined Scale factor
|
CALC |
CALC |
CALC |
CALC |
Rotation - rotation between two coordinate systems |
0 |
CALC |
CALC |
CALC |
N Residual, E Residual - residuals on the horizontal plane |
0 |
0 |
CALC |
CALC |
Vertical Plane
|
Note: To perform localization in vertical plane, check the Use Vertical box for minimum ONE point. |
H0 - vertical offset between two coordinate systems |
CALC |
CALC |
CALC |
CALC |
Deflection North, Deflection East- deflection components |
0 |
0 |
CALC |
CALC |
Ht Residual - residuals on the vertical plane |
0 |
CALC |
0 |
CALC |
When you check Rotation Only for a localization point, you need add to localization one or more localization points with Use Horizontal or Use Horizontal and Use Vertical status. For this case MAGNET Field will calculate:
- when using localization point(s) with Use Horizontal and Use Vertical - DX, DY, H0, Rotation, Scale, Deflection North, Deflection East, NResiduals, EResidual, Ht Residuals;
- when using localization point(s) with Rotation Only - Rotation, NResiduals, EResidual, Ht Residuals.
If a geoid model is set in the job, MAGNET Field will use this geoid model for calculating orthometric height (elevation).
The current version of MAGNET Field enables you to perform the horizontal localization in three ways:
- Using default (the stereographic) projection on WGS84 (Find out more...).
- Using default (the stereographic) projection on any datum (Find out more...).
- Using any predefined or created projection (Find out more...).
Localization
In the dialog you can select the type of localization and see the points are used in the calculation of the transformation parameters.
- Select the Type of Localization. You can see the following types:
- WGS84 ->Local; For the plane localization will use the stereographic projection on WGS-84. If you perform a task of transformation of WGS-84 coordinates into Ground coordinates for a network where the maximum distance between the local points is less than 5 kilometers, you can use this localization type. Before localization you need to set in the Coordinate System dialog: Projection <none>; Datum WGS-84.
- Datum -> Local; For the plane localization will use the stereographic projection on selected datum. If you know which datum is used for the local coordinate system, you can use this datum in localization. Before localization you need to set in the Coordinate System dialog: Projection <none>; Datum ANY_Datum.
- Grid->Local; If you know which projection is used for the local coordinate system, you can use this projection in localization. In this case this projection and corresponding datum will be used in the process of calculation of localization parameters. Such approach to the calculation of the localization parameters between two coordinate systems is more rigorous method, than using the stereographic projection for a unknown local projection. This way allows increasing the distance between localization points (up to some hundred of kilometers depending on the type of the projection) without loss in transformation precision. Before localization you need to set in the Coordinate System dialog: Projection ANY_Projection; Datum Datum_for_Projection.
- Click Add to open the Add Localization Point dialog for adding control point(s). The quantity of points required for localization depends on how these points are used in localization parameters calculation.
Note: The localization is recomputed every time a new point is added to the list of localization points. The new coordinate system will be saved under the name "Localization" and is automatically selected in the Coordinate System dialog.
- Check the Keep scale box to use the value of 1.0 to preserve the localization from a scale transformation or enter the desired scale factor to reduce the grid localization to the ground. With cleared check box (default state), the scale factor will be calculated according to the number of localization points.
- If needed, click Edit to open the Edit H/V Controls dialog to change how these points are used in localization parameters calculation.
- Click Remove to remove the highlighted points pair(s).
- Click Details to view the results of the localization.
- Click
to apply changes and exit the Localization dialog.
Note: In specific cases, clicking
you can receive a message that reads "Please check pair X". In such a case, the following actions are required:
1. Select the pair in the list of point pairs in the Localization dialog.
2. Click Edit.
3. Click
. You will get a message that contains problem description and recommended solution.
Click
to open the dialog menu with additional options. More...
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Pop-up menu of Localization
The pop-up menu contains a set of the following options:
- Edit Points
- Export to File opens the To File dialog, where you can select the desired file format to export the transformation parameters. The Export to File menu item is enabled, when the localization type is WGS84 -> Local.
- Localization Origin is enabled, when one or more pairs of points are selected for localization, and the option is used for the WGS84 -> Local localization type. You can select one of the following:
- Center of Localization Points (default setting) - the geometrical center of pairs of points, which is used in localization, becomes the center of the default map projection.
- First Localization Point - the first pair of points, which is used in the localization, becomes the center of default map projection.
- Legacy Mode is enabled when one or more pairs of points are selected for localization. Select it to set the Legacy mode for the horizontal localization. We recommend you to select this mode when you import the Topcon 3D localization file (*.gc3), which was created by all versions of Topcon Tools, TopSURV, Pocket 3D, 3D-Office and versions 1.* of MAGNET Tools and MAGNET Field. If this mode is not selected (by default), the default mode is applied. We recommend you to select default mode when you import the Topcon 3D localization file (*.gc3), which was created by MAGNET Tools and MAGNET Field from version 2.0. When you import Localization file into the opened job and you click the Use Legacy Localization check box, the Legacy mode is automatically set.
Add Localization Point / Edit H/V Controls
In the dialog you can add known point and measured point to localization or to edit localization controls of existing localization point.
- Select the localization control where the point will be used:
- Rotation Only - the localization point is used for the determination of rotation between two coordinate systems only. Using one point is not enough to perform localization. Need to add one or more point with "Use Horizontal" or "Use Horizontal"/ "Use Vertical" status. When performing localization, the software calculates:
- the rotation between two coordinate systems using point(s) with "Rotation Only" and point(s) with "Use Horizontal" or "Use Horizontal"/ "Use Vertical "status;
- the offset and scale between two coordinate systems using point(s) with "Use Horizontal", or "Use Horizontal"/ "Use Vertical "status.
- Use Horizontal - check the box to use the point in the horizontal localization. You can select one, two, three and more localization points in this plane. For each case the application will calculate a different set of transformation parameters and residuals.
- Use Vertical - check the box to use the point in the vertical localization. You can select one, two, three and more localization points in the plane.
Note: To obtain horizontal and vertical (3D) coordinates for points after localization, there must be minimum one localization point with Use Horizontal and one localization point with Use Vertical check box enabled, or one localization point with both Use Horizontal and Use Vertical check boxes enabled.
- In the Known Point field, enter the Point in the local (ground) coordinate system. You can enter the point manually or select it from the map
or from the list
of the job points.
-
In the Measured Point field, enter the Point in the coordinate system that is set for the current job. You can enter the point manually, select it from the map
or from the list
of job points. For the GNSS device type, you can also measure the point coordinates by clicking
.
In the measure point coordinates dialog:
- The # field shows the number of the accepted epochs (the parameters of the logging are set through the
Settings button).
- You can overwrite, rename, or store the point as a check point.
- You can select the Code for this point and click
to set the point's attributes. More...
- Click
to save the point and return to the Localization dialog with a newly added point.
Click
to open the dialog menu with additional options:
Localization Details
The Localization details dialog displays the input and calculated parameters of the localization:
- Localize To: the name of the projection (datum) of the current job to which the localization was applied.
- Rotation: the rotation angle between the projection (datum) and local coordinate systems.
- Scale: the scale factor between the projection (datum) and local coordinate systems.
- Offsets: the offset vector between the origins of coordinate systems.
- North: the horizontal component of the offset vector on the X axis.
- East: the horizontal component of the offset vector on the Y axis.
- HO: the vertical component of the offset vector.
- Deflections: the vertical deflection.
- North: the North component.
- East: the East component.
- Geodetic Origin: geodetic coordinates of the first localization point from the projection (datum) set in the coordinate system of the current job.
- Lat: the latitude of the first localization point.
- Lon: the longitude of the first localization point.
- Ht: the ellipsoidal height of the first localization point.
- Local Origin: local coordinates of the first localization point from the local set in the local coordinate system.
- North: the northing coordinate of the first localization point.
- East: the easting coordinate of the first localization point.
- Ht: the orthometric height of the first localization point.
- Quality estimation: the coordinate transformation error.
- Hz error: the coordinate transformation error in the horizontal plane.
- Angle error: the angular error of the coordinate transformation.
The Map tab displays all points of the job. Localization points are marked by blue triangles showing how this point is used in current localization:
-
- localization point is used in horizontal and vertical localization;
-
- localization point is used in horizontal localization;
-
- localization point is used in vertical localization;
-
- localization point is used for the determination of rotation between two coordinate systems;
-
- localization point is not used in current localization.
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