Closed strings, as in a circle, square or any irregular polygon A closed string is one whose first and last co-ordinates are the same If more than one closed string exists in a

file with the same string number, then these are called closed segments of that string and are assigned a segment number. This is common in situations where many features, all

3. A spot height string, being a set of random points linked together by a string number,

but outlining no particular feature. The points can be in any order, as the actual line joining them does not represent a feature you can see. Spot height strings are commonly used for recording elevations of points on a surface, or coordinates of bore holes.

Use of String Kinds

In survey applications it is more common to deal with open strings which define discontinuous features, as are found in open pits, with closed strings being used as boundary strings to constrain a volume computation.

Engineers and geologists tend to be more involved with closed strings, such as bench crests and toes, ore outlines etc. Such closed strings may be assigned a thickness and can therefore be used in calculation of both areas and volumes.

String Descriptions

The ability is provided to be able to assign other `non-coordinate' information to each point in a string. This data is called the point description. In surveying, this is usually exactly what it is, e.g. a description or name of a control station. When dealing with closed strings, it is more usual that the point description will contain attributes of the feature enclosed by the string, e.g. the concentration and total salinity of a water sample.

The point description may contain sub-fields, which can be used to address individually for various purposes. These may include:

• storing assays for multiple elements, e.g. total contaminant calculations

• plotting various description sub-fields for a point at different locations about the point. The description sub-fields are referred to as D1, D2, D3 up to a maximum of D100. They may be generally referred to as D fields.

The D fields are delimited by commas. In the following example DESCRIPTION = ``TREE, 1.54, HOUSE''

The sub-fields have the values: D1 = ``TREE''

D2 = ``1.54'' D3 = ``HOUSE''

The total length of the description field may not exceed 512 characters regardless of the number of sub-fields.

String Directions

The convention is to plot a string number at the first point of a string. Depending on how a particular string was created, the order of the points will sometimes give a clockwise direction for the string segment and sometimes an anticlockwise one. This direction of segments is important to closed strings when calculating areas and volumes.

If a closed string is defined in a clockwise direction, it is assumed it represents a positive area; that is an area of inclusion.

If it is defined in an anticlockwise direction, it is assumed it represents a negative area; that is, an area of exclusion.

If an anticlockwise closed segment of a string is contained within a clockwise closed segment, the combination is effectively defining the area between the closed segments.

String Files

Related strings are stored together in ASCII files called string files, identified by an .str extension. A string file can contain up to 32000 different strings

Each file is identified by a two-part name - the two parts are nominated separately in practice, but they are combined to form a filename acceptable to the computer on which the software is being run. The first part is called the Location code. This is an

alphanumeric character identifier usually chosen to indicate what the strings in the file represent, e.g. contour, borehole, buildings etc.

The second part is an ID number defining the file as a member of a set of files. This is a numeric character identifier.

For example, a set of files, each containing surveys for an underground mine for the months January, February and March 1990 may be called:

LEV9001 LEV9002 LEV9003

Where LEV is the common location code in each case, and the ID numbers are the year/month code of the individual files containing the surveys.

If you type a decimal number in an ID, for example 1.65:

• the number is rounded to one decimal place, with 0.05 rounded up (that is, 1.65 rounds to 1.7);

• the one-decimal-place number with the decimal point excluded (that is, 17) will be used for referring to the ID;

• refer to the one-decimal-place number, either with or without the decimal point (that is, either 1.7 or 17), when recalling the file.

String File Structure

Each line in a string file is called a record. The first two records are called the header record and axis record respectively. The header record contains data relating to the whole string file such as the location code, date formed and the purpose.

The axis record contains two sets of co-ordinates identified as string number zero, defining a 3-dimensional axis, which is used when taking sections. If no axis has been defined, this record will hold zeros.

The rest of the records in a string file contain points on the strings, with each record having the following structure.

string number Y X Z point descriptions

Each field is delimited by a comma. Records containing zeros in all of the first four fields indicate the end of a segment or string. The final record in the string file is a line with a string number of zero and END in the descriptor field.

The following example string file (pump1.str) was created using the GROUNDWATER

MODELLING module and contains the definitions of three pumping wells. The file

contains five description fields, (D1 - D5): borename, Time pump on (days), Time pump off (days), Pumping rate (kl/d) and Pumping bore radius.

pump ,26-Mar-92,pumping wells ,

0, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000 100, 28.275, -47.079, 0.000, recover1 ,0,10000000,500,0.15 100, 117.516, -93.714, 0.000, recover2 ,0,10000000,700,0.2 100, 108.160, -26.973, 0.000, recover3 ,0,10000000,500,0.15 0, 0.000, 0.000, 0.000, 0, 0.000, 0.000, 0.000, END

The second string file (blocks98.str) below shows an example of a string file containing closed segments.

The file was created using the GEOSTATISTICS module and contains regular blocks with a grade calculated using an inverse distance algorithm.

blocks , 1-May-92,Grade classifications of blocks98.str , 0, 0.000, 0.000, 0.000, 0.000, 0.000, 0.000 1, 285.000, 115.000, 98.000, 0.035,23.035 1, 295.000, 115.000, 98.000, 0.035,23.035 1, 295.000, 125.000, 98.000, 0.035,23.035 1, 285.000, 125.000, 98.000, 0.035,23.035 1, 285.000, 115.000, 98.000, 0.035,23.035 0, 0.000, 0.000, 0.000,

0, 0.000, 0.000, 0.000, 2, 35.000, 55.000, 98.000, 4.367,11.462 2, 45.000, 55.000, 98.000, 4.367,11.462 2, 45.000, 65.000, 98.000, 4.367,11.462 2, 35.000, 65.000, 98.000, 4.367,11.462 2, 35.000, 55.000, 98.000, 4.367,11.462 0, 0.000, 0.000, 0.000, 3, 55.000, 55.000, 98.000, 8.941,57.704 3, 65.000, 55.000, 98.000, 8.941,57.704 3, 65.000, 65.000, 98.000, 8.941,57.704 3, 55.000, 65.000, 98.000, 8.941,57.704 3, 55.000, 55.000, 98.000, 8.941,57.704 0, 0.000, 0.000, 0.000, 5, 65.000, 45.000, 98.000, 26.785,36.595 5, 75.000, 45.000, 98.000, 26.785,36.595 5, 75.000, 55.000, 98.000, 26.785,36.595 5, 65.000, 55.000, 98.000, 26.785,36.595 5, 65.000, 45.000, 98.000, 26.785,36.595 0, 0.000, 0.000, 0.000, 0, 0.000, 0.000, 0.000, END

DTM’s

Digital Terrain Models or DTM’s are how Surpac models surfaces. Surfaces are used in Surpac for such things as 3D visualization & calculating volumes. Most any superficial feature can be modelled as a DTM: natural topography, lithological contacts,

bedrock/overburden contact, or water table are such examples. DTM’s must come from String data. String files contain the raw data, where as DTM files contain a mapping of trios of points in the String file that constitute a triangle. DTM’s are made of triangles, with each point of each triangle matched to a point in the original String file.

Consequently DTM files are not valid without the original String files. That is, a DTM file cannot be opened if the original String file of the same name does not exist. Another rule as far as DTM’s are concerned is that DTM’s cannot fold back on themselves. That is, a DTM cannot have multiple Z values for a given XY coordinate.