Calc Module
A classical geodetic calculator designed to provide:
- Convert and transform coordinates between two user-selected coordinate reference systems
- Perform distance and azimuth computations between pairs of points (known as forward and reverse computations)
- Provide file conversions with user defined file format specifications
- Full compliance with EPSG database and ISO terminology
Benefits
- Simple user interface
- Direct link from EPSG database for geodetic parameter definition
- User-defined file format function
- Inventory of pre-defined file formats provided, e.g. UKOOA P1, SEGP1
- Conversion and Transformation algorithms comply with EPSG guidance notes 7-2
- Reverse and forward computations provided
CRS Parameter selection
Prior to computations being performed the CRS parameters for both Point A and Point B must be supplied. This can be done in one of two ways:
1. If the user is already within the DB module the CRS being examined can be selected at that point to populate the calulator (see DB module).
2. The CRS can be selected from the ‘CRS definition wizard’ provided within the calculator. Details of this are shown below:
The CRS list provided, within the user panel, meets the criteria of the filtered options selected above (e.g. show all the 2D geographical CRS systems within the UK). All displayed parameters are extracted directly from the Geo DB module and thus honour the EPSG geodetic database. The i (information) icon in the bottom right corner provides a direct link to the database to enable the CRS parameters to be viewed in more detail.
Integral to the tool are the geodetic parameters used to define the coordinate reference systems and the algorithms used to perform the mathematics.
Calc provides an elegant user wizard to select the FROM and TO coordinate reference systems. The wizard incorporates a series of filters (described above) that narrow the selection listbased upon geographical area and coordinate system type selected by the user.
Single Point Conversions
Once FROM and TO CRS’ have been selected the main panel of the Calculator will display the selections made along with the basic parameters associated with each CRS. The Calculator can now be used to perform computations. The basic computation is that of a single point conversion where by the coordinates of a point are entered into either Point A or Point B and the conversion or transformation is performed between the two by clicking on the required arrow button in the middle column.
File Conversions
The file conversion function enables a collection of points to be converted and / or transformed from one input file. The ‘import wizard’ enables a input file format to be defined and thus does not restrict the user from pre-conditoning the file prior to use. The wizard guides the user through a series of steps that define the location of the coordinates contained within the file (e.g. row and column definition). An inventory of common exchange file formats are also recognised in addition to well known text and .prj files.
The converted data is exported to a user selected file. The coordinates can be either appended to the original import file or written to a new file. Details of the coordinates being exported are displayed within the main panel of the ‘Process File’ user panel
Reverse and forward computations
The reverse and forward computation modes enable computations to be performed to compute distance, angular and coordinates between pairs of positions. The relationship is shown below and comprises seven parameters, namely: Two angular (forward bearing and reverse bearing), four positional (two coordinates for point A and two coordinates for point B) and one distance (s – geodetic or plane distance between point A and point B).
Reverse Computation
The reverse computation enables the distance and bearings (forward and reverse) to be computed between pairs of points when the coordinates of the two points is known. The coordinates of point A and point B will be added to the boxes provided and Calc will determine the three unknown parameters. The answers are displayed in the box provided.
As shown on the user panel, the computations can be performed on ellipsoidal surface or a plane surface. It is recommended that the computations are performed on the ellipsoidal surface for accuracy.
Forward computations
The forward computation enables the coordinates of point B to be computed when the coordinates of point A are known along with the distance and bearing to point B. The reverse bearing from point B back to point A is also determined as part of the computation.
The coordinates of point A are entered into the fields provided. The Forward button is selected and a secondary panel will appear requiring entry of the distance and bearing to point B. Once provided the coordinates of point B along with the reverse bearing will be determined.