Aerial survey of land and sites around Tiverton

There is significant parkland in this parish, and parkland behaves differently from a field under the camera. Mature standing trees in cropped grass throw large moving shadows, hold their own canopy well above the ground, and hide whatever sits underneath them.

A surface model of parkland is therefore a model of the tree tops and the grass between them, and no processing produces the ground beneath a full crown. For most estate work that is fine, because the questions are about extent, condition, drives, drainage and the state of the grass. Where levels under a canopy have to be measured, that is laser scanning work rather than photography, and it is better to hear that at the quote than after the invoice.

The Grand Western Canal runs through here as a long thin feature, and a long thin feature needs a different flight from a square parcel. A corridor survey is flown as a strip with overlap along its length and enough width either side to hold the banks, the towpath and the ground behind them.

Anything linear behaves that way: a canal, a leat, a hedge line under dispute, a length of track, a pipeline route. The frame count climbs with the distance rather than the area, so a mile of corridor and a compact field of the same acreage are quite different jobs to price.

Tiverton sits where the Lowman meets the Exe on ground that climbs sharply north and west, and the farms above the town are on genuine slopes. As on the Creedy, a survey planned flat over that gets uneven ground detail and, at the top of a rise, less clearance than the plan assumed.

The other thing slope does is fill the frame with shade. A north-facing valley side in winter can sit in shadow for most of the short flying day, and shadow is missing information as far as the model is concerned. On the steep holdings here, the time of day is part of the plan.

This stretch of the Exe valley is notably wet, well above the county average, which shortens the number of days a survey can actually be flown. Nothing about that is solved by turning up anyway.

The practical answer is a booking that carries a fallback date, and a willingness to take a good day when it appears. Repeat sites are easier still: the plan is already written down, so a return visit can be flown at short notice whenever the weather opens.

Alongside the farms and the estate land there are large institutional grounds in this town, which bring their own considerations. Playing fields, drives, car parks, mature trees and a lot of people who are not part of the survey, all on one site.

The A2 Certificate of Competency governs how close the aircraft may work to people who are not involved in the job, so on ground like that the answer is timing rather than technique: fly out of hours, or fly the sections that are clear and come back for the rest. Where a site cannot be cleared at all, that is said before the visit is booked.