Photogrammetry Archives - The Survey Association

Why not all photogrammetry surveys are equal

Rachel Tyrrell — Wed, 12 Aug 2026 08:12:01 +0000

Photogrammetry has become more accessible than ever. With drones, high-resolution cameras and powerful software now widely available, it’s easier to produce visually impressive models. It is important to understand that not all photogrammetry surveys deliver the same quality or the same level of accuracy. A model might look convincing on screen. That does not mean it can be relied on for design, engineering or construction decisions.

High quality images

Good data begins with good digital images. Higher-quality digital cameras capture more detail, sharper features and less distortion. Images need to be well-focused and consistently exposed too. Poor lighting or inconsistent image quality can reduce clarity. This makes it harder for software to correctly match features between digital photos. This results in reduced accuracy and potentially unreliable outputs.

Planning is critical

A photogrammetry survey is never simply a case of flying a drone and taking pictures. Successful projects rely on careful planning, including designed flight paths or camera positions, consistent image overlap and appropriate viewing angles. Missing areas or uneven coverage can lead to gaps in the data or distortions in the final model, so getting the coverage right from the start is essential.

Ground control’s important role

One of the biggest differences between a visually impressive model and a survey-grade dataset is the use of ground control points (GCPs). These are accurately surveyed reference points on the ground that anchor the model to real-world coordinates and significantly improve positional accuracy. Without GCPs, a model may look good but lack the accuracy required for precise measurement or integration with other survey data.

The human factor

Despite advances in automation, photogrammetry is still a professional surveying activity. Technology is a powerful tool but it is geospatial survey expertise that ensures the results can be trusted. Experienced geospatial surveyors bring critical expertise, including the skill to plan the survey properly, check and validate results and ensure outputs are fit for purpose.

What about accuracy?

Modern photogrammetry can achieve very high levels of precision, sometimes down to millimetres in ideal conditions. However, this depends on good planning, high-quality imagery and proper control and processing.

What this means for clients

Good photogrammetry is not defined by the technology, it is defined by how it is used. When commissioning a survey, it’s important to look beyond the visuals. Consider how the data will be captured, how accuracy will be controlled and whether the outputs will meet your project needs. A well-executed survey will provide reliable, reusable data. A poorly executed one may need to be repeated, involving delay and extra costs.

TSA is leading a national marketing campaign in a drive to gain greater recognition for geospatial surveying; photogrammetry is just one of the many specialisms of the profession. Found out more about the national marketing campaign and TSA’s Unity Charter here.

For detailed guidance on specifying photogrammetry surveys, understanding accuracy, and choosing the right provider, download the full client guide from TSA’s website. TSA publishes a range of guidance notes on different aspects of surveying – access all our guides here.

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How photogrammetry works (without the jargon)

Rachel Tyrrell — Wed, 01 Jul 2026 09:28:37 +0000

Photogrammetry might sound complex, but the basic idea is surprisingly simple. At its core, it works because the same object looks slightly different when viewed from different positions. By analysing these differences, software can work out where things are, what shape they are, and how big they are. Basically, photogrammetry uses multiple digital photos to build an accurate 3D picture of the real world.

The principle behind photogrammetry

If you walked around a building and took digital photos from lots of different angles, each image would capture a slightly different view. Photogrammetry software compares these different images, identifies common features across them, and uses this information to calculate their precise position.

A useful way to think about it is comparing it to how people see the world. Each of our eyes sees a slightly different view and our brain combines them to create depth. Photogrammetry does the same thing, but instead of two images, it might use hundreds or even thousands.

The three key steps involved in the photogrammetry process

While the process is highly technical behind the scenes, it can be broken down into three main stages:

1. Understanding the camera

Before anything else, the software needs to understand how the camera “sees” the world. Every lens introduces small distortions, so the system accounts for these to ensure measurements are accurate. This step is often called camera calibration.

2. Matching images and building the model

Next, the software searches across all the photos to find matching features, points that appear in multiple images.

By linking thousands of these points together, it builds a 3D framework known as a point cloud. This forms the foundation of the final model.

3. Placing it in the real world

Finally, the model is tied to real-world coordinates using surveyed control points.

This step, known as georeferencing, is what turns a visual model into accurate, usable survey data that designers and engineers can rely on.

Why overlap matters in photogrammetry

One of the most important requirements in photogrammetry is image overlap. Each digital photo must share a significant amount of common ground with the next, typically 60-80%. If there isn’t enough overlap, gaps can appear in the data, accuracy is reduced and the final model may be unreliable. So, good data capture is just as important as good processing.

Why this matters for clients

Understanding the basics helps you ask the right questions and ensures you get data you can trust.

The process may happen behind the scenes, but the impact is huge. The quality of the final output depends on professional planning, coverage, and control, not just the software used.

Photogrammetry is now more accessible than ever, but producing reliable, accurate survey results still requires professional expertise.

For detailed guidance on workflows, accuracy, and specifying photogrammetry surveys, download the full client guide from The Survey Association website.

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Photogrammetry in the modern world

Rachel Tyrrell — Thu, 08 Oct 2015 15:56:49 +0000

TSA recently ran its newly introduced technical short course on “Practical Photogrammetry” at The Survey School in Worcester. The course was conducted by recognised industry expert Clive Boardman and was held over three days.

The aim of the course is to demystify the technique of photogrammetry which has become ever more important in recent times with the development of lightweight small aerial platforms and “off the shelf” processing packages.

Most commonly associated with stereo photography and the production of maps, photogrammetry is now an accepted method of data collection in almost any sphere of measurement and competes well with other methods despite still retaining a slight air of mystery about it.

The course includes both classroom and outdoor field work in a total of six sessions. The classroom sessions concentrate on theory, camera calibration, control requirements, rectification and the use of multi-image processing software. The outdoor sessions concentrate on image capture. Most of the image processing software used in the course is now available at realistic prices and opens up the technique to a whole new audience.

The course can only take six students at a time and was fully subscribed within a day of promoting it. It will be run again in December and quarterly thereafter and it is anticipated that the course will form part of the regular short course offering from The Survey School.

Thanks should go to EOS Systems in Canada for the loan of multiple PhotoModeler licences and Agisoft for their support.

The feedback from the students indicated that the balance of theory versus practical was ideal and all attendees stated that they would recommend the course to others.

More information on the photogrammetry course can be found here.