Photogrammetry Benchmark

This article talks about how to get the best results out of the process of photogrammetry

To get the most out of this benchmark, please refer to the main Photogrammetry page for the core underlying theory behind achieving a successful result.

Photogrammetry

Benchmarking Elements

The key goal is to provide the software with enough features and consistent information so that it can successfully align your photos, and triangulate it into 3D spatial data.

	Non-Optimal	Optimal
Quality	Inconsistent or widely varied	Consistent and cohesive photo-set
Variation	Unable to take many varied photos	Able to take lots of varied photos
Feature Points	Not many	Many
Overlap	Unable to overlap photos	Able to overlap all photos

Quality is a basic necessity to achieve a good result, if you foresee too much variation in the overall lighting and environment, it is recommended to reconsider the photogrammetry subject.

Variation in photos is required to build a complete result, if you foresee that you would be unable to take many photos from different perspectives and distances, reconsider the photogrammetry subject.

Feature Points as mentioned above are required, these are influenced by the geometry and its materiality.

Overlap is required for the alignment process other than feature points, ensure that photos overlap so that feature points can be correlated across images to align them.

Base Techniques

Technique	Description
Pathing	Ensure you can walk around the object comfortably
Camera Settings	Use a DSLR camera, keeping it on Auto will do
	Ensure same focal length (use a fixed lens or no zoom) and use the same camera

Benchmark Guide

The following guide (in no particular order) is a way to identify qualities that impact the ability for the software to align photos and detect depth. By default, some subjects have differing qualities in this benchmark than others that may detract or improve alignment and depth processing. Recommendations for dealing with each feature are provided to help improve the process.

These alerts signify a quality that is difficult to overcome, if these become applicable to your photogrammetry subject we recommend that you do not proceed with it. You are always welcome to book a consultation with us to discuss and plan your approach.

Environment

	Non-Optimal	Optimal
Background	Dynamic with lots of motion	Static
	Very high contrast Featureless	Balanced contrast
Lighting	Dynamic, changing Too light or too dark, obscures details	Static or consistent Natural, overcast - slightly sunny so details are all visible with some contrast
Ease of Photography	Unable to take different perspectives	Able to take many, varied perspectives
	Can only take photos from one fixed distance.	Can take photos from many distances

Background Techniques

A dynamic environment, such as a moving crowd or dynamic weather patterns means that there is too much variation for the software to identify similar features across the photo set.

TIP: The background environment can be a great tool to help in photo alignment as it provides context. This is applicable for objects with low geometric or visual features.

Technique	Description
Time	Restrictions to access or limited activity. E.g. after hours for a public sculpture

Lighting Techniques

For the software to easily recognise features for alignment, it is desirable for the photo-set to be consistent. Very dark or overexposed parts of the subject can lead to incorrect alignment and it is also common for these features to just go missing as the software has trouble picking up depth. Depth is best read with subtle shifts in shadows as a gradient.

Technique	Description
Time	Take photos when lighting is less harsh
Flash/LED	A flash can help with underexposed, overly dark areas if the object is not too far away.
Camera	If you have experience with photography, switching to manual settings gives you more control over exposure and can help with ensuring a consistent photo-set.

Ease of Photography Techniques

It is best to reconsider the subject for photogrammetry if you are unable to take varied perspectives from many different distances.

Perspectives: A varied set of angles provides more information to produce a more complete 3D model. As the camera has direct vision like human eyes do, we encourage to directly take photos of everything you want to include. This will increase efficiency of software in aligning the photos.

Proximity: If there is too much obstruction in the area due to crowds or other objects, it may hinder your ability to to take photos from a variety of proximities. Photos from far-away to mid-range, will give more improve alignment.

Technique	Description
Tripod/Extensions	A tripod or a selfie-stick could help in extending your range, allowing for more angles to be reached.
Markers On Subject	If you are forced to get really close to an object due to space restrictions, you may end up too close to capture any significant feature points. In this case, markers can be put on the subject to add a set of references for the software to align with. See Technical Guides - Advanced Techniques

Geometric Features

Quality	Non-Optimal	Optimal
Motion	Subject is dynamic, even swaying in a breeze	Completely static
Features	Very few or almost no perceivable detail	Feature Rich
Variation	Repeated elements	Lots of unique/asymmetrical features
Detail	Very tiny or thin	Large objects with big dimensions
Visibility	Aspects of the subject are inaccessible by camera	All aspects are accessible through the camera

Motion

Motion is usually inherent to the subject so it is hard to control, examples include things like kinetic sculptures or objects that light up dynamically.

It is best to reconsider the subject for photogrammetry if subject cannot be made static nor have a static phase. Capturing a dynamic subject using photogrammetry is not ideal.

Features & Variation Techniques

Depending on what can be captured in frame, it is ideal to maximise the amount of different geometric features.

Large amounts of featureless geometry, such as a blank plaster wall, will not have enough feature points for the software to align with.

Repeated elements can confuse the program as the feature points are very similar. For example, the facade of a skyscraper. Usually this is not a problem as lighting, small inconsistencies/imperfections can act as feature points.

Technique	Description
Markers On Subject	Markers can be used to by the software to help distinguish between two photographs that consist of very similar and repeated geometry and features. See Technical Guides - Advanced Techniques
Use the Environment	If the area around the subject, in the near background or the ground, is feature-rich, then you should try to include as much of the environment as possible to improve alignment.
Pathing	Plan out your pathing differently by ensuring more overlap or capture other kinds of features in frame by moving back.

Detail Techniques

Photogrammetry, and digital reconstruction technologies in general will struggle capturing extremely thin or small subjects especially if the subject is comprised primarily of fine details. Objects smaller than 500mm will struggle to have any detail retained, and objects thinner than 500mm will struggle to have their thickness captured.

Technique	Description
Markers Around Subject	Markers placed around the subject, such as on attached geometry or in the background or ground can be used for alignment instead of the subject, this will allow the subject to still be generated as a 3D model, but rougher. See Technical Guides - Advanced Techniques
Use the Environment	If the area around the subject, in the near background or the ground, is feature-rich, then you should try to include as much of the environment as possible to allow the software to use it as part of the alignment process.

Details like carpet texture or hair are considered very thin, the resulting 3D model will not be able to generate each individual strand, but only the overall shape. There are no techniques to help with this.

Visibility Techniques

If you need something in your model, you need to have a photo of it.

Technique	Description
Pathing	Ensure you plan before hand what angles you will need to take. A good technique is to split the subject into various sections and photograph each section rigorously. As long as you include photos that can align sections together, or there is enough information between two sections, it will usually work better.
Chunking	Consider separating the model into various sections, you can apply photogrammetry in sections and piece them together. Using markers will help in the alignment process as you can use these to join sections together. This is very common for capturing both the underside of an object.
Tripod/Extensions	A tripod or a selfie-stick could help in extending your range, allowing you to photograph any inaccessible or hard-to-reach areas.

Visual Features

	Non-Optimal	Optimal
Contrast	No contrast	Balanced Contrast
Colour	Single flat colour	Varied colour, to the point of patterns and asymmetry
Texture	Smooth	Asymmetrical, varied textural details
Repetition	Repeating patterns	Lots of unique features

Techniques

Visual Features refer to the surface quality or materiality of the object. A wall covered in graffiti is the perfect example of optimal Visual Features compared to a blank brick wall.

All the qualities of Visual Features do not need to be maximised for good results, as any one of them should be enough to give enough information for alignment. Usually, variation given by the light/environment and imperfections on surfaces can be enough to offset any lack of visual features.

Technique	Description
Markers On Object	Markers can be used to by the software to help distinguish between two photographs that consist of very similar visual features. See Technical Guides - Advanced Techniques

Transparency/Reflectivity

Quality	Non-Optimal	Optimal
Transparency	Transparent completely	All opaque
Reflectivity	Completely reflective; mirror-like	All opaque

Techniques

As transparent objects allow light to pass through, a masking agent that covers the surface can be used to make it recognisable by the software. A removable/cleanable, matte spray paint is ideal as it can be applied with an even coating. Masking tape is a cheap alternative.

If you are unable to make the subject opaque, we recommend choosing a different subject all together.

Technique	Description
Masking	Use a removable/cleanable matte spray paint so that it can be captured on camera.
	Apply masking tape so that it can be captured on camera