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| IntroductionIn Geocap it is the responsibility of the user to secure that data have the correct Datum and Coordinate system, also called a Projection. Datasets with the same geographical location but with different coordinate system will not be displayed in the same graphical window. Thus, you will need to convert one of the datasets to the other coordinate system. |
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GEOTRANS
Geocap uses GEOTRANS for geodetic conversion of coordinates. The following statement applies: The product was developed using GEOTRANS, a product of the National Geospatial-Intelligence Agency (NGA) and U.S. Army Engineering Research and Development Center.
Through GEOTRANS, Geocap can convert datasets between more than 200 Datums, and 32 different projections and coordinate systems. See the full list in the Appendix.
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Converting datasets
The command menu is the same for all conversions, however there has been made four instances of it with pre-defined settings, for your convenience:
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Note that Geocap will ask you to specify the coordinate system for the original dataset if it does not contain any geodetic properties. |
Earth Distance Calculations
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Using Geocap you can easily calculate the shortest distance between two points following the earth's curvature. This is done with the calculate earth distance dialog. The dialog is opened from the main menu under Geodesy.
Select Calculate earth distance and the dialog will appear.Select the datum and coordinate system of the data in the display window. You can also select which unit you want for distances. Default unit is in meters. You can also select which distance calculation method you want to use. Flat earth calculates the distance between the two points as a straight line. Flat earth will automatically use Earth centered sphere if the selected coordinate system is geodetic. Earth centered sphere approximates the earth as a sphere with a constant radius. Radius adapted sphere approximates the earth as a sphere, but uses the radius of a sphere with the same curvature as the ellipsoid used by the selected datum, at the midpoint between two points. Ellipse approximation calculates the distance along the ellipsoid using an approximation algorithm.
The dialog will calculate the latitude and the longitude of the last selected point. It will also calculate the distance between the last two selected points. A point is selected by clicking in the display window in 2D mode. In 3D mode you can use the y key on the keyboard to select points on a surface. The distance calculations will not use the z value (that is the height value) in its calculations.
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Menu for correction distance calculation