Using SnakeGrid

User interface

The user interface is divided into three bands. In the application management area the user can access the help file and load the required parameter file. Once this has been loaded (see below) the selected grid will apply to either single point conversion or multiple point conversion.

	Application Management Area
	Single Point Conversion Area
	Multiple Point Conversion Area

The single point and multiple point modes are described in separate sections below.

Loading a parameter file

At start-up the coordinate conversion boxes will be greyed out and the program cannot be used. It will continue so until an appropriate parameter file has been selected.

To load a parameter file, simply click on the “Open Snakegrid Parameter File” button and this will bring up a dialogue box allowing the file to be browsed for and loaded in the usual way.

If a valid parameter file is opened, the point conversion boxes will be activated and the title bar will change to read “SnakeGrid” followed by the name of the grid. The user should check that the correct one has been loaded – this name will also be printed on the first line of any output file. In the image below it can be seen that the parameter file relating to the grid ABCGrid_2008 has been loaded.

Once a parameter file has been loaded it is not possible to load another without exiting the application. This is to prevent accidental re-loading of a different parameter file during subsequent use.

Only parameter files that have been created expressly for the SnakeGrid software may be used. These have been encrypted to prevent the use of invalid files.

Single point conversion

The conversion of individual points between ellipsoidal and grid coordinates is carried out within the “single point conversion” area in the middle of the user interface. This may be carried out in either direction.

Simply fill in the values in the boxes shown, and then convert by pressing the arrow. The right arrow converts ellipsoidal coordinates to grid, and the left arrow performs the conversion from grid to ellipsoidal.

The ellipsoidal coordinates are to be entered in decimal degrees, with North and East the positive directions. When entering values it is helpful to bear in mind that 0.000 000 01 degrees (10^-8) is approximately 1mm – therefore eight places of decimals are shown when the conversion is made from grid coordinates.

The Easting and Northing values in the boxes shown are in the system of the grid named in the title bar. They are in metres, with three decimal places as standard.

Batch conversion

Input and output formats supported

 Tabulated below are the file formats currently supported by SnakeGrid. It should be emphasised that ONLY latitude and longitude OR easting and northing are relevant to the coordinate conversion. However, in order to handle pre-existing file formats in which the points are associated with IDs, heights, code strings, and so on, there is the option to read these in and write them to the output file alongside the converted coordinates.

The following generic points apply to the tables below:

If the “Ignore header” box is ticked then the program will ignore the first line of the input file. Any further lines of header will be treated as incorrectly formatted points.

Files may be tab delimited or comma separated. The software will automatically determine which type the input file is.

For ellipsoidal coordinates:

For grid coordinates:

For each of the above, comma separated format is an acceptable alternative. For example, LL5 could be of the form:

P129.A,51°,09',21.95560",N,2°,28',16.48343",W

The format of the output file may be any of those listed above, provided that the information required is present. That is, a format specifying ID for example cannot be selected if it was not supplied in the input file. However, a format that shows less information than the input file is acceptable. Once the format of the input file is selected, only the permissible output formats will be shown.

The permissible combinations of input and output file formats are shown in the table below:

Either tab delimited or comma separated format may be selected for the output file by clicking the appropriate button in the output file area.

Conversion procedure

To convert files, first select the direction of the conversion – that is, whether it is to be from ellipsoidal to grid or vice versa. This is indicated by the buttons in the middle of the lower part of the screen:

The input file can then be selected by simply pressing the “Open Input File” button and navigating in the conventional way. The file found is shown in the left hand window at the bottom. The format is selected from the list shown.

Next select or assign an output file in a similar way by pressing “Open Output File”. This can be made comma separated or tab delimited by clicking the appropriate button. The name of the selected file is shown in the right hand window at the bottom.

Finally, press “process” and the conversion will be carried out. The progress is shown in the window indicating the number of points processed so far.

Once the processing is complete the name of the output file will be cleared in order to prevent accidental overwrites.

The output file will always show a header that names the grid in the first line, followed by the data headers.

Should any input point not be accepted the output file will write for that line “Invalid point:” followed by a reproduction of the line of the input file. The rest of the file will be unaffected.

There are two main reasons for a point being marked as invalid. Either it is not within the acceptable geographic area (has the right parameter file been loaded?) or the format is incorrect. This may have come about through – for example – accidentally specifying LL2 format when it is in LL1, and so the software is failing to find ID and height values on each line.