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PLACESTP: Lay Out a Systematic Sample in a Rectangular Area

      PLACESTP is used to determine the coordinates of a systematic layout of test units (of any size) within a rectangular area. It can either provide an optimal placement of test units (optimal in the sense that the size of the largest circular site that can be missed by the testing program is minimized; see Krakker et al. 1983, Kintigh 1988), or can determine the coordinates of test units with a user-specified spacing. This program's output file can be used directly by STP to determine the effectiveness the testing strategy.

      Three different systematic layouts of test units are supported: (1) a simple rectangular grid; (2) a staggered rectangular grid in which adjacent rows of test units are offset by one-half the test unit spacing along the transect; (3) a hexagonal grid in which each 3 adjacent test units form an equilateral triangle.

      The user first defines the length and width of a rectangular (or square) survey area. The program views that rectangle as placed on a coordinate system with its length along the X axis and its width along the Y axis, and the origin (0,0) point at the lower left hand corner of the rectangle. The program operates by placing transects of test units along the length of the survey area. The program output includes the coordinates of test units with the specified layout and various statistics on the test unit layout.

       There are no practical limits to the size of the area or number of test units that can be handled by the program.

 OPERATION OF PLACESTP

       The PLACESTP program is started from the command line. The program then prompts the user for all information that it needs to run. The prompts issued by the program are described below. For more information about the conventions used in these prompts, see the section entitled "Program Conventions."

       To start PLACESTP type: PLACESTP<Enter>. Once this is done, you will see this message:

 Length of Area to be Sampled ?

       Enter the length of the rectangular survey area. Any unit of measure can be used, but the unit of measure must be consistent throughout.

 Width of Area to be Sampled ?

       Enter the width of the rectangular survey area. The width must be less than the length.

 [H]exagonal, [S]taggered, or [G]rid Test Units {H} ?

       Choose the test unit layout. Enter H, S, or G. Hexagonal (equilateral) spacing provides the best coverage. A Staggered grid is a diamond-shaped layout with test units on adjacent transects offset. A reply of G for Grid obtains a standard rectangular grid of points.

 [O]ptimal or [S]pecified Spacing {O} ?

       If optimal spacing is desired, the program will position the transects adjacent to the lengthwise edges of the survey area Optimally, so that no larger sites will be missed along the edge than would be missed between transects. (The calculations required to do this are, in most cases not obvious. The formulae are given in Kintigh 1986.) With Specified spacing you determine the spacing between transects; the program centers the specified set of transects within the width of the survey area.

 Number of Lengthwise Transects ?

       Enter the number of transects desired that run the length of the survey area. Adjacent transects will be equidistant, with borderline transect locations determined by the previous prompt. For purposes of this program, all transects run lengthwise.

       If Specified spacing is requested, you will receive the following two prompts:

Interval Between Units Along Transects ?
Interval Between Lengthwise Transects {20.95} ?

       Only if Specified spacing is requested, these prompts allow you to specify the interval between units along the transects and the spacing between the transects, given the total number of transects given in the previous prompt.

Test Unit Size: Area (+) or Diameter (-) {0.0} ?

      Enter the test unit size. If the program is used only to obtain coordinates, the default value (0.0) may be entered. However, if the output of this program is to be used with STP, then a test unit size should be entered. The size may be entered as either an area or as a diameter. Enter areas as positive numbers, e.g., for a 1 m x 1 m test unit the entry of 1.0 indicates an area of 1.0 square meter. Enter diameters as negative numbers, e.g., -.40 indicates that each test unit is .4 units in diameter. Make sure that these values are in same units as the length and width. For example if the length and width are given in meters, then the diameter must be given in meters, e.g. -.40, not in centimeters (-40). If a diameter is given then the area of the test unit is reported as follows:

Test Unit Diameter: 0.40
Test Unit Area: 0.13

 Output File Name {.TXT} ?

       Enter the name of the file in which the program output is to be placed. The output file consists of the four x-y pairs of coordinates of the corners of the survey area on one line, followed by three values on one line for each test unit: the x and y coordinates, and the test unit size. If the named file already exists, you will be prompted to make sure that it is OK to replace it.

       The basic statistics of the test unit layout are included in the program output that is directed to the screen. These numbers are generally self explanatory. For example:

 Number of   Test Unit Interval        Spacing        Maximum Diameter 
Test Units    Along Transects     Between Transects   of Untested Site 
   23                24.74               21.43              28.57

      A minor word of caution should be interjected concerning the maximum diameter of an untested site. First, this applies only to sites whose centers fall within the survey area. Obviously, arbitrarily large sites with their centers outside the survey area could go untested. Second, for layouts with optimal spacing there is a minor boundary effect: it is possible that sites having their centers within the survey area and with diameters larger than the specified maximum may exist along the short ends of the survey area. For layouts with a user-specified spacing, the maximum diameter of an untested site does not apply to sites with their centers outside the array of test units (i.e., along any boundary).

 Program End

       Message that lets you know that the program has ended properly and that you can now use your output file.

SAMPLE SESSION

      The following lines show a sample interactive session with PLACESTP.

PLACESTP<Enter>

Length of Area to be Sampled ? 100<Enter>
Width of Area to be Sampled  ? 100<Enter>
[H]exagonal, [S]taggered, or [G]rid Test Units {H} ? <Enter>
[O]ptimal or [S]pecified Spacing {O} ? <Enter>
Number of Lengthwise Transects ? 5 

Test unit size, if positive, is interpreted as an area or, if 
  negative, as a test unit diameter.  Remember to use the same 
  unit of measure as was used in the length, width, and spacing 
  above, e.g. if length was in meters, area is in m2 or diameter 
  is in meters (not cm). 

Test Unit Size: Area (+) or Diameter (-) {0.0} ? -.40<Enter>
  Test Unit Diameter:  0.40 
  Test Unit Area:    0.13 
Output File Name {.DAT} ? test<Enter> 
File Exists; OK to Erase It {N} ? Y 
TEST.DAT Erased 
  
 Number of   Test Unit Interval   Test Unit Spacing   Maximum Diameter 
Test Units    Along Transects     Between Transects   of Untested Site 
   23                24.74               21.43              28.57 
  
Program End

SAMPLE OUTPUT

    0.00      0.00    100.00      0.00    100.00    100.00      0.00    100.00
      0.51      7.14 0.126
     25.26      7.14 0.126
     50.00      7.14 0.126
     74.74      7.14 0.126
     99.49      7.14 0.126
     12.88     28.57 0.126
     37.63     28.57 0.126
     62.37     28.57 0.126
     87.12     28.57 0.126
      0.51     50.00 0.126
     25.26     50.00 0.126
     50.00     50.00 0.126
     74.74     50.00 0.126
     99.49     50.00 0.126
     12.88     71.43 0.126
     37.63     71.43 0.126
     62.37     71.43 0.126
     87.12     71.43 0.126
      0.51     92.86 0.126
     25.26     92.86 0.126
     50.00     92.86 0.126
     74.74     92.86 0.126
     99.49     92.86 0.126

Page Last Updated: 17 October 2020