Importing Control Points

Control point data can be imported in a tab delimited .gcp (text format) file:

§  First line (optional): Define the control points’ coordinate system in WKT format. (Default: geographic Lat-Long WGS84.)

#wkt=……

Note:       The WKT information must be in a single line without any line breaks. You can use the Coordinate System Generator to generate a WKT string defining the required coordinate system. See “Coordinate System” in the “Basic Concepts” chapter for more information.

§  Second line (optional): Indicate the number of control points. If this information is not provided, each subsequent line in the file is interpreted as providing positioning information for a distinct control point. If the file includes this information, all lines after the number of lines in cp=[number] are interpreted as mapping between control points and photos.

cp=[number]

§  For each control point, set the control point’s position on the terrain (X, Y, Altitude (Optional), Name (Optional), Type (Optional; Possible values: 1-control; 2-check; 3-tie) in tab delimited format.

[x coordinate] <TAB> [y coordinate] <TAB> [altitude] <TAB> [name] <TAB> [type]  

Note:       The Type parameter can only be passed together with the Name parameter.

Note:       The altitude base is assumed to be "GEOID”. If you want to change the altitude base, you can select all the control points after import and change the altitude base value in their property sheet.

§  Specify the position (in pixel coordinates) in a specified photo to associate with a particular control point (referenced by index).

[control point index] <TAB> [photo file path] <TAB> [x pixel coordinate] <TAB> [y pixel coordinate]

Example:

#wkt=GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4326"]]

cp=2

9.63390819201651 <TAB> 47.4233597051724 <TAB> 401.463806152344 <TAB> Control point1

9.63390818337074 <TAB> 47.4233597019402 <TAB> 401.463793239556 <TAB> Control point2

0 <TAB> C:\Photos\1.tif <TAB> 384 <TAB> 5456

0 <TAB> C:\Photos\2.tif <TAB> 7689 <TAB> 4761

0 <TAB> C:\Photos\3.tif <TAB> 8738 <TAB> 4340

1 <TAB> C:\Photos\4.tif <TAB> 388 <TAB> 5450

1 <TAB> C:\Photos\5.tif <TAB> 7690 <TAB> 4761

1 <TAB> C:\Photos\6.tif <TAB> 8741<TAB> 4326

To import control points:

1.      On the Home tab, in the Add group, click the arrow under Control Points and select Import. The Import Control Point File dialog box is displayed.

2.      Browse to the required .gcp file and click Open.

3.      Modify the control point properties as required, and then save the project.