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Layer Transformation

CivilGEO’s software uses a projected coordinate reference system (CRS) to create an engineering model. It lets the user bring in GIS, CAD, TIN, and other data files which are in a different coordinate system, and automatically map them according to the project CRS.

However, sometimes when a projection file layer with data that has been converted from 3D spheroid (Earth) survey data into a projection map is added to a project, it may not necessarily map in the same coordinate space as the rest of the data. This issue occurs because all map projections have distortions.

The transformation scale factor is a way to reduce the distortion over a particular area so that a dimension on the flat projection map is as close as it can get to the spherical Earth measurement. AutoCAD Civil 3D provides support for the transformation scale factor in its Drawing Settings dialog box.

In our software, the transformation scale factor is supported throughout the software, including CAD layers, TIN layers, and other layers.  This is accomplished by using the layer properties dialog boxes to automatically apply the transformation scale factor on any particular layer and accurately map it to the project coordinate reference system (CRS).

In addition, a layer’s position may be registered manually by providing two coordinate points (i.e., the source and the target location).

Follow these steps to apply a layer transformation and its registration on the desired layer:

  1. From the Map Data Layers panel, click the […] button of the desired layer.
  2. The layer Properties dialog box will be displayed.
  3. Select the Transformation tab.

The following sections describe how to use the Transformation tab and how to interact with the above dialog box.

Apply Grid Scale Factor

This option permits the application of grid scaling factor on a layer to match the layer’s dimensions to the project CRS. The Grid scale factor is the measure of distortion at a point on a projected map. It is used to calculate the actual ellipsoidal distances as per the true shape of the Earth, which is not a perfect sphere. To apply grid scale factor on a layer, follow these steps:

  1. Turn on the Apply Gird Scale Factor check box to enable layer transformation using a grid scale factor.
  2. Enter the Grid scale factor value.
  3. Click the [OK] button. Now, this grid scale factor will be applied to the layer’s dimension.

Apply Reference Point Shift

This option allows quick registration of a layer that is not mapped correctly according to the project CRS. The user can specify the coordinate points for the target and the source locations. To apply reference point shift on a layer, follow these steps:

  1. Turn on the Apply Reference Point Shift check box to enable the option.
  2. Enter the corresponding Easting and Northing coordinates in the Local reference point (target) and the Grid reference point (source) entry fields.

Alternatively, the user can interactively pick the target and source locations from the Map View to automatically register the layer. To use this alternate method, follow these steps:

  1. Click the [Pick] button corresponding to the Local reference point (target) section.
  2. The layer Properties dialog box will temporarily disappear, and a prompt will be displayed on the status bar “Pick target reference point.
  3. Click the point on the Map View that will serve as the reference for the target location.
  4. The layer Properties dialog box will redisplay.
  5. Click the [Pick] button corresponding to the Grid reference point (source) section.
  6. The layer Properties dialog box will again temporarily disappear, and a prompt will be displayed on the status bar “Pick source reference point.
  7. Click the point on the Map View that will serve as the reference for the source location.
  8. The layer Properties dialog box will redisplay.
  9. After defining the locations, click the [OK] button, and the software will automatically transform and register the selected layer based on the user-defined criteria.

About the Author Chris Maeder

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