Calibrated Photogrammetric Scale Bars
Cultural Heritage Imaging (CHI) is now offering a set of professionally calibrated scale bars for highly accurate measurement during scientific photogrammetric imaging of 3D data. These scale bars are uniquely suited to today's practice of close range photogrammetry. The unrivaled scale bar design was developed and field-tested by a senior team of photogrammetry experts from the US Bureau of Land Management.
Scale bars are flat, lightweight linear bars in several sizes with printed targets separated by a known distance. To enable the measurement of an object or a site in 3D you place the scale bars on, around, or next to the imaging subject. (The scale bars ship with a user guide that has detailed instructions). When a series of images is processed to create a 3D model, the processing software — we use Agisoft PhotoScan Pro — finds the exact center of the targets on the scale bars in the set of photos. Once the professionally calibrated, written measurement of the distance between the targets, is entered in the software, the measurement of any feature of the imaging subject becomes possible.
These aren’t just any scale bars! Our scale bars are:
- Designed by senior photogrammetry experts at the US Bureau of Land Management for highly accurate measurement and scientific imaging in photogrammetry projects
- Each scale bar individually calibrated by CHI staff to 1/10th mm or better accuracy
- Printed on Dibond, a tough, durable composite material consisting of 2 aluminum sheets bonded on either side to a solid polyethylene core
- No delamination or warping, optimized for long-term outdoor use, water- and environment-resistant
- Three types of coded and non-coded targets to meet a variety of needs (see product details below)
- High-frequency details on the grayscale background enable the generation of a measurable 3D model of the entire scale bar
CHI's calibrated scale bar sets are now available to ship!
|Download the US Domestic Order Form (PDF)|
|Download the International Order Form (PDF)|
The price of each set of scale bars is $495.00 plus a cost of between $15–$23 for UPS ground shipping in the US, depending on the destination. We charge sales tax for scale bar sets shipped within California.
We ship internationally via USPS (United States Postal Service), which transfers the package to your country's local postal service for delivery. if you prefer to use a different carrier, let us know. To determine international shipping and handling costs in advance, contact us at firstname.lastname@example.org.
We can accept credit cards, Electronic Fund Transfers (EFT), checks, and purchase orders. If you choose to pay by credit card, we will send you an invoice that includes a link to enter your credit card information using a secure server. At that time you can pay with any major credit card or with a PayPal account. Please let us know what you prefer.
If you have any questions about the scale bars, please send an email to email@example.com; include your location if you have questions about shipping. If you need to have your department information and/or a purchase order number included on your invoice, please send us that information, and we will email an invoice back to you. We will ship your scale bars to you after we have received payment or a p.o. number from your institution.
CHI provides a set of 10 scale bars: 2 each of 5 sizes, 6 coded, 4 non-coded.
Coded Scale Bars
Three sizes of the scale bars have 12-bit coded targets. The coded targets are automatically detected and named by several photogrammetry software packages, including Agisoft PhotoScan Pro. The automatically detected names (represented by numbers) of the coded targets are different on all the bars in a set, and CHI offers 10 different sets with unique coded targets. This is useful if more than one set of scale bars is needed in a project. The different target designs ensure that the processing software can manage those targets as unique and not confuse them with other targets within the same 3D project.
Non-coded Scale Bars
The non-coded targets come in two styles.
- The black circle on the meter scale bar can be located by the user in large projects to manually select the target. This is necessary if the imaging resolution of the scale bar is insufficient for automated detection due to large-scale subjects like sites and landscapes, as in cases where the camera may be distant from the subject. The circular design with a white dot in the center enables the software to locate the center of the target automatically.
- The other non-coded, cross-type targets (alternating quadrants of black and white within a circular boundary) are found on the small scale bars (18cm and 5cm), and the cross-hatch design allows some software packages (including Agisoft PhotoScan Pro version 1.1 and later) to detect them automatically as targets, placing a marker at the center of the circle where the black and white sections intersect.
Specifications of Each Type of Scale Bar
Note: Our scale bars are calibrated by CHI staff to 1/10 mm accuracy or better, with the actual calibrated measurement between each target written on the scale bar.
Meter Scale Bars (2)
Each bar uses 3 coded and 2 non-coded circular targets. Centers of each target are approximately 25 cm apart, with a total distance from targets on each end of 1 meter. Each bar’s overall dimensions are 108cm x 6cm tall.
Half-meter Scale Bars (2)
Each bar uses 3 coded targets. Centers of each target are approximately 25cm apart, with a total distance from targets at each end of 1/2 meter (or 50cm). Each bar’s overall dimensions are 60cm x 6cm tall.
Quarter-meter Scale Bars (2)
Each bar uses 2 coded targets. Centers of each target are approximately 25cm apart. Each bar’s overall dimensions are 35cm x 6cm tall.
18cm Scale Bars (2)
Each bar uses 2 non-coded, circular cross-type targets. Centers of each target are approximately 18cm apart. Each bar’s overall dimensions are 23cm x 6cm tall.
5cm Scale Bars (2)
Each bar uses 2 non-coded circular cross-type targets. Centers of each target are approximately 5cm apart. Each bar’s overall dimensions are 10cm x 6cm tall.
Questions About Scale Bars?
Please send email to firstname.lastname@example.org.
Note: The calibrated photogrammetric scale bars come with a limited warranty. Read the warranty…