Visual Impact Assessment Guidebook

Appendix 6

Choosing an appropriate visual simulation presentation technique

Choose the appropriate presentation technique for the perspective view based on:

complexity of the proposed operation(s);
number of viewpoints and visual sensitivity class (previously visual sensitivity rating);
level of public involvement;
silvicultural system proposed; and
number and location of landmarks easily identified on both topographic map and photographs.

Freehand sketching requires some practice and is generally used only in low-risk situations where accurate representation of the proposed operation is not critical. A more accurate and effective approach is a photo overlay.
In the field or based on photographs, record on sketches the main forms and lines of the landscape and some of the variety, such as forest type change, rock outcrops, and existing openings.
Estimate and draw the shape and position of the proposed operation.
Develop sight lines from specific viewpoints to increase reliability and accuracy.
Refer to the Ministry of Forests booklet An Introduction to Graphic Communication (1994) for details on how to sketch. This booklet is available from the Forest Practices Branch upon request.

Photographic overlay is relatively easy to apply, but requires backup maps and sight-line information to be reliable and accurate.
Place an acetate overlay on top of photograph and locate the proposed operation on the landscape by matching landscape features, such as rock outcrops, meadows, and timber type boundaries, on photographs with the same features observed in the field.
Refer to Appendix 3 for photographic presentation criteria.

Take a photograph from the important viewpoint(s) used in the assessment.
Develop a simple wire-frame DTM from the photo locations using the same parameters as for taking the photograph (i.e., same lens size and same horizontal and vertical viewing angles).
Plot the DTM to match the size of photo used; alternately reduce the wire-frame DTM onto acetate overhead material using a photocopier.
When the reduced DTM matches the photograph perspective, overlay DTM acetate on top of the photograph and colour the proposed operation to match as closely as possible the final appearance.

This simulation should provide an accurate representation of size, shape, and location of the proposed operation relative to the photo image.

Computer simulations are usually necessary in situations where: the terrain is complex or indistinct; a high public concern is evident; or multiple proposals are visible from one or more viewpoints, or one proposal is visible from more than two viewpoints.
Computer simulations are also used to predict forest operations over several passes or over an entire rotation period.

Import TRIM data and digitized or scanned contour map data to generate a DTM for the area being evaluated.
Digitize all existing and proposed cutblocks and roads.
Produce simulations from the same viewpoint previously used in the field for taking photographs. A stereoscopic pair can be produced by offsetting the viewpoint. An approximate offset of 100 m per km of distance from the target will provide an easy-to-view, three-dimensional image. Several offsets may be necessary to produce the desired image.
To simulate a cutblock, some software programs add trees to the model surface while others counter-sink the block into a rendered surface. Whichever process is used, it is necessary to specify the average height of the trees in the vicinity of the proposed block. This information can either be measured in the field or derived from forest cover inventory data. After a visual simulation has been completed, it should be labelled with information identified in Appendix 5 (i.e., digital terrain model presentation criteria).

Digital retouching allows the merging of DTM output with scanned photographs. The final product realistically simulates the appearance of proposed operations.
This technique may be required in high-sensitivity areas and when public presentations are required.

Note: Not all visual simulation techniques are required for all visual impact assessments.