## Surface Patch (SP)

```Purpose:  To input parameters of a single surface patch.

Card:

Cols        Parameter
----------------------
1- 2        SP
3- 5        I1 - blank
6-10        I2 - NS
11-20        F1 - X1
21-30        F2 - Y1
31-40        F3 - Z1
41-50        F4 - X2
51-60        F5 - Y2
61-70        F6 - Z2
71-80        blank

If NS is 1, 2, or 3, a second card is read in the following
format:

Cols        Parameter
----------------------
1- 2        SC
3- 5        I1 - blank
6-10        I2 - (see Notes)
11-20        F1 - X3
21-30        F2 - Y3
31-40        F3 - Z3
41-50        F4 - X4
51-60        F5 - Y4
61-70        F6 - Z4
71-80        blank

Parameters:
Integers
(I1) -  not used
NS  (I2) -  Selects patch shape
0: (default) arbitrary patch shape
1: rectangular patch
2: triangular patch

Decimal Numbers

Arbitrary shape (NS = 0)

X1  (F1) - X coordinate of patch center

Y1  (F2) - Y coordinate of patch center

Z1  (F3) - Z coordinate of patch center

X2  (F4) - elevation angle above the X-Y plane of
outward normal vector (degrees)

Y2  (F5) - azimuth angle from X-axis of outward
normal vector (degrees)

Z2  (F6) - patch area (square of units used)

Rectangular, triangular, or quadrilateral patch (NS = 1, 2, or 3)

X1  (F1)    X coordinate of corner 1

Y1  (F2)    Y coordinate of corner 1

X1  (F3)    Z coordinate of corner 1

X2  (F4)    X coordinate of corner 2

Y2  (F5)    Y coordinate of corner 2

Z2  (F6)    Z coordinate of corner 2

X3  (Fl)    X coordinate of corner 3

Y3  (F2)    Y coordinate of corner 3

Z3  (F3)    Z coordinate of corner 3

For the quadrilateral patch only (NS = 3)

X4  (F4)    X coordinate of corner 4

Y4  (F5)    Y coordinate of corner 4

Z4  (F6)    Z coordinate of corner 4
```
Notes:
• The four patch options are shown in figure 5a b c d. For the rectangular, triangular, and quadrilateral patches the outward normal vector n is specified by the ordering of corners 1, 2, and 3 and the right-hand rule.
• For a rectangular, triangular, or quadrilateral patch, t1 is parallel to the side from corner 1 to corner 2. For NS = 0, t1 is chosen as described in section II-2.
• If the sides from corner 1 to corner 2 and from corner 2 to corner 3 of the rectangular patch are not perpendicular, the result will be a parallelogram.
• If the four corners of the quadrilateral patch do not lie in the same plane, the run will terminate with an error message.
• Since the program does not integrate over patches, except at a wire connection, the patch shape does not affect the results. The only parameters affecting the results are the location of the patch centroid, the patch area, and the outward unit normal vector. For the arbitrary patch shape these are input, while for the other options they are determined from the specified shape. For solution accuracy, however, the distribution of patch centers obtained with generally square patches has been found to be desirable (see section II-2).
• For the rectangular or quadrilateral options, multiple SC cards may follow a SP card to specify a string of patches. The parameters on the second or subsequent SC card specify corner 3 for a rectangle or corners 3 and 4 for a quadrilateral, while corners 3 and 4 of the previous patch become corners 2 and 1, respectively, of the new patch. The integer I2 on the second or subsequent SC card specifies the new patch shape and must be 1 for rectangular shape or 3 for quadrilateral shape. On the first SC card after SP, I2 has no effect. Rectangular or quadrilateral patches may be intermixed, but triangular or arbitrary shapes are not allowed in a string of linked patches.