### SYNOPSYS

void slaPcd(disco, x, y)

double disco
double *x
double *y

### DESCRIPTION

```
Apply pincushion/barrel distortion to a tangent-plane [x,y].

```

#### Given

```     disco    double      pincushion/barrel distortion coefficient
x,y      double      tangent-plane coordinates

```

#### Returned

```     *x,*y    double      distorted coordinates

```

#### Notes

```
1)  The distortion is of the form rp = r*(1 + c*r2), where r is
the radial distance from the tangent point, c is the disco
argument, and rp is the radial distance in the presence of
the distortion.

2)  For pincushion distortion, c is +ve;
For barrel distortion, c is -ve.

3)  For x,y in units of one projection radius (in the case of
a photographic plate, the focal length), the following
```
disco values apply
```
geometry          disco

astrograph         0.0
schmidt           -0.3333
AAT pf doublet  +147.069
AAT pf triplet  +178.585
AAT f/8          +21.20
JKT f/8          +13.32

4)  There is a companion routine, slaUnpcd, which performs
an approximately inverse operation.