Slope and Planarity (ITF CS 03/03)



Ideally, a tennis court should be a flat surface lying in a single horizontal plane. The court may be sloped for drainage, but the single plane of the surface should always be maintained.

The slope should be oriented to minimise its effect on play. Thus, where a court must be sloped for drainage, a slope from side-to-side is preferred (see Figure 6).

The slope is determined by measuring the ratio of change in elevation to horizontal distance. Planarity is measured relative to a hypothetical plane parallel to the slope of the court.

Preferred orientation of slope

Figure 6. Preferred orientation of slope (side-to-side), if necessary.


Apparatus

Test apparatus consists of:

- A distance-measuring device, calibrated to ± 0.05%, such as a laser distance meter or a steel tape.

- A surveyor’s level, calibrated to ± 1 mm/10 m, and a measuring staff, calibrated to ± 0.25 mm. The level may be either a self-levelling rotary laser, which sweeps out a horizontal plane with a beam of visible or infrared light, or an optical level, where the plane is defined by the horizontal axis of the instrument.

The distance-measuring device and measuring staff must be checked against known standards. This should be carried out at appropriate intervals (typically annually) or if there is any reason to suspect that the device is inaccurate and/or has been damaged, (e.g. if a laser distance meter has been dropped or left in the rain, or a steel tape has become kinked).

A surveyor’s level may be checked using the standard ‘two-peg’ method: Place the level midway between two pegs at different heights 10 m apart and read the staff on each peg. Calculate the height difference between the pegs. Move the level 1 m past one of the pegs and read the staff on each peg and calculate the height difference again. The difference in the height differences is the collimation error in mm/10 m.


Test procedure

1. Using the distance-measuring device, find the x- and y-coordinates of the corners of the TPA (B2, B6, H2 and H6 in Figure 4). Temporarily mark a 7.5 m grid on the court surface (e.g. using coins). The centre point of the grid will be at the midpoint of the net, and the perimeter of the grid encloses the PPA (C3, C5, G3 and G5 in Figure 4).

2. Using the surveyor’s level, establish a horizontal reference plane using a fixed datum, e.g. by placing the level near the centre of the court. Measure the vertical distance between the surface and the horizontal reference plane at the four corners of the TPA and each of the 15 points of the PPA grid (19 points in total) using the measuring staff.

3. Repeat the measurements in reverse order. Check any measurement for which the discrepancy between the two values exceeds 1 mm.

4. Measure the evenness of the court at the 19 points (refer to method ITF CS 02/02).


Calculation of results

Slope

1. Calculate the height difference for each pair of points along the two sides of the PPA and take the mean of these five values.

2. Divide the difference between the two mean values by the width of the PPA (15.0 m) to give the side-to-side slope.

3. Repeat this method to determine the end-to-end slope (using the points along the ends of the PPA, divided by 30.0 m) and the two corner-to-corner diagonal slopes (using the corner points of the PPA).

4. The maximum of these four gradients is the test value for slope.

Planarity

1. Calculate the mean of all the level measurements in the PPA to give the height of the centre of a hypothetical plane parallel to the court.

2. Calculate the heights of this hypothetical plane at each of the PPA and TPA points using the side-to-side and end-to-end slopes.

3. Use the evenness measurements from step (4) of the test procedure to correct the height, i.e. add the depth of a hollow, or subtract the height of a bump.

4. Calculate the height difference between the surface and the ideal plane at each measurement point. The maximum difference is the test value for planarity.


Recommendations

Refer to Table 4.

Table 4. Evenness, slope and planarity recommendations for a tennis court
Table 4. Evenness, slope and planarity recommendations for a tennis court.

Notes: PPA = Principal Playing Area; TPA = Total Playing Area.

1. Specifications are for porous constructions. For impervious constructions, see ‘acrylic’.
2. In no instance should any imperfection exist that could cause the ball to deviate significantly from its path on a level surface, or expose a player to a significantly increased risk of injury within the perimeter of the court.
3. Deviations on clay or grass over 6 mm should be corrected where possible.
4. Unless design, specification or construction necessitate otherwise.

Note: A steeper maximum gradient is given for acrylic, impervious asphalt and concrete courts to prevent water from collecting on the court. In the case of clay and grass, a shallower gradient is required to minimise the erosion of the top dressing.