How HARVEY maps are made - Photogrammetry

A map is one of the most trusted pieces of equipment for safe navigation, and as such needs to be highly detailed, reliable and up to date. In addition, at HARVEY Maps we consider mapmaking to be an art as much as a science!

How do we make our maps? Where does our data come from? Our maps are crafted at our HQ in Doune, Scotland, by our highly skilled team of photogrammetrist's and cartographers. Pete, our senior photogrammetrist, takes us through the process of map making at HARVEY Maps in the first of two blogs.

Introduction
Choosing an area to map is the first step. There are lots of areas in the UK and Ireland that we have still to map so the team must research and agree on an area for the next new map. They need to decide on the map format and whether it's a sheet map containing lots of exciting hills, or a long distance path map like the South West Coast Path.

All our data is original and created from scratch using aerial photography. Historically, aerial photographs were supplied as prints which were set up in manual stereo plotting machines like the Swiss made Wild A8 or the Italian Stereosimplex G6. We have a working example of this, a WildA8-1221, at our HQ in Doune. These days the aerial photography is digital and the process is achieved using specialist software and a fast processor!

Once the relevant data has been captured it is sent to our cartographers who then make sense of all the lines, add text and additional information and produce something which is recognisable as a map.

The map is then tested on location where a thorough survey check is carried out. Once final changes/edits have been made, the map is sent to the printers. From inception to finished product the time taken to produce a single map can be anything from four to nine months.

Photogrammetry
The creation of the map starts with photogrammetry, which is the process of extracting 3D information from photographs. We begin by doing a 'photo search' to see what aerial photos are available and when they were taken. On occasion it will be necessary to commission a certain area to be flown.

Photos are taken by a special high precision camera fitted to a light aircraft flying at a height of between 4000-7000m. The plane flies on a straight course, taking photographs of the ground at regular intervals. Each photo is taken with a 60% photograph overlap, and the co-ordinates of the centre point location is precisely recorded.

This allows the strip of photos to be georeferenced to the ground, and the overlap allows the land to be seen in 3D. Viewing through stereo eyepieces provides the operator with an elevated view of the terrain and a birds eye perspective.

Every detail is accurately recorded with painstaking care, selecting features that are useful to people navigating the terrain. The features that we want to appear on the map (tracks, buildings, woodland, marsh, stony ground, contours, etc) are recorded in separate layers. The accuracy of this data is approximately 5m in plan position and 1m in height. The hallmark of HARVEY mapping is its clarity and detail, and precisely plotted contours, supplemented by rock information.

Once this stage is complete, and the photogrammetrists have recorded the detail of the terrain, it is the turn of the cartographers to turn the data into a readable map.

Visit our Map Shop and Map Bothy and find out first-hand how we make maps.

Next up: How HARVEY Maps are made - Cartography & Survey




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