Photomontage methodology in a landscape and visual assessment

A verified photomontage exists to let a decision maker see, as accurately as a flat image allows, what a proposal would look like from a given point. Photomontage methodology in an LVIA is therefore a question of reproducibility: could another practitioner stand where the camera stood, using the stated equipment, and produce the same image. If not, the view is an illustration rather than evidence, and an inspector will treat it accordingly.

The recognised landscape assessment guidelines set the framework for the assessment itself. The professional guidance on visual representation of development proposals then defines a hierarchy of visualisation types, from an annotated viewpoint photograph through wirelines to fully verified photomontages, and states what each requires.

Choosing the right visualisation type

Match the type to the purpose, and say which type each figure is.

An annotated photograph records the baseline view and is appropriate where the proposal is not visible or where the assessment is scoping.

A wireline shows the proposal's outline over the photograph or over a terrain model. It is quick, it is honest about what it does not show, and for a distant view of a linear structure it often communicates more than a rendered image.

A rendered photomontage that has not been verified is presentation material. It has a place in consultation and no place in evidence.

A verified photomontage carries surveyed camera positions, a registered model and an accuracy statement, and it is what a contested inquiry needs. Producing a small number of verified views is better than producing many unverified ones.

Survey control and camera position

The camera position has to be recorded to national grid coordinates and to a stated height above ground, using survey-grade positioning rather than a phone.

Record the date and time, the weather and visibility, the bearing of the view and the equipment used. Where the view depends on seasonal screening, record whether vegetation was in leaf.

Control points are what make registration checkable. Identify fixed features visible in the photograph whose positions are known or can be surveyed, such as building corners, masts or road furniture, and list them with their coordinates. A reviewer can then test the registration independently.

Photographs should be taken from a tripod at a consistent eye height, conventionally around 1.5 metres, in conditions with adequate visibility. A view shot in haze that hides the site is not a baseline, and substituting a clear-day image from a different date without saying so is the kind of error that damages an entire assessment.

Lens, focal length and print size

The convention is a fixed focal length around 50 millimetres on a full-frame sensor, which approximates the angular relationships the eye perceives in the central field.

Where a wider field is needed, produce a panorama by rotating the camera about the correct axis and joining the frames in a stated projection, rather than using a wide-angle lens, which distorts scale relationships at the edges.

Print size and viewing distance then have to be stated together, because they are what preserve the angular relationship. An image that is correct at A1 viewed at arm's length is wrong when reproduced at A4 in a committee report, and the figure should carry the intended print size and viewing distance in its title block so that anyone reproducing it knows what they are changing.

Model registration and the accuracy statement

Registration is the step where the three-dimensional model is aligned with the photograph so that the camera in the model matches the camera on site.

The model should be built on survey data or reliable terrain data, with the proposal positioned by coordinates rather than by eye. Once registered, the accuracy of the alignment is tested against the control points, and the residual error reported.

The accuracy statement is the document that makes the montage evidence. It should record the survey method and equipment, the coordinate system, the control points used, the registration method, the residual errors, the software, and the name and role of the person who carried out each stage. Where any element was approximated, say which and why.

Two further points matter at inquiry. State whether the rendering shows materials and colours as proposed or as neutral surfaces, because a neutral render understates visibility of a reflective or pale building. And state whether adjacent consented schemes are included.

Who does the work, and why that shows

Verified views are produced by three sets of hands: a surveyor establishing camera positions and control, a modeller building and registering the geometry, and a visualiser rendering the image. On small commissions one person does all three, which is fine provided the competence is there for each stage.

Where it goes wrong is at the joins. A camera position surveyed to the wrong datum, a model built in a local coordinate system and registered by eye, or a render produced from a viewpoint that drifted between iterations, each produce an image that looks convincing and cannot be reproduced.

Name the person responsible for each stage in the methodology section. It takes three lines and it tells a reviewer where to direct any question.

Seasonal and cumulative scenarios

Vegetation changes what is visible. Summer views with full leaf cover routinely understate visibility, so the convention on schemes screened by deciduous planting is to present winter views, or both.

Where the scheme relies on proposed planting for mitigation, present the view at year one and at a stated later year, with the growth assumption named. An image showing mature planting at completion is misleading and will be identified as such.

Cumulative assessment covers other schemes that are built, consented or the subject of undetermined applications. Define which category each falls into, and produce cumulative views where they change the judgement. Viewpoint selection itself is a separate exercise, covered in our note on viewpoint selection for townscape and visual assessment.

Limitations to state in the report

1. That a photograph cannot reproduce the dynamic, binocular experience of a view, and that the montages support rather than replace a site visit.
2. The print size and viewing distance each figure assumes.
3. The weather, visibility and season in which each baseline photograph was taken.
4. Any approximation in the model, including assumed heights of surrounding features.
5. Whether materials are rendered as proposed or neutral.
6. Which other schemes are included in cumulative views, and their planning status.

Stating limitations strengthens the assessment. A report that claims the images show exactly what will be seen invites cross-examination on the one point where the technique is weakest.

Illustrative example, for method only. A scheme on rising ground is assessed from eight viewpoints. Two are verified photomontages at A1 with stated viewing distances, taken in winter with leaf-off conditions and supported by surveyed camera positions and residual errors under the tolerance stated in the guidance. Four are wirelines. Two are annotated baseline photographs where the proposal is not visible. The inspector has a proportionate set of evidence, and the two verified views carry the weight.

The visual work then feeds the written assessment in the Landscape and Visual Impact Assessment, with townscape effects covered separately in a Townscape and Visual Impact Assessment where the setting is urban.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

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