Surveying and Construction Pros — Must See: Achieve High-Precision Location Data for Construction Photos and Streamline Workflows with LRTK

Table of Contents

• Why location information is necessary for construction photos

• Challenges in conventional construction photo management

• Benefits of improving location accuracy

• High-precision positioning realized with RTK technology

• What is the smartphone GNSS device "LRTK"?

• Achieve centimeter-level location data for construction photos with LRTK

• Efficiency gains from using LRTK

• Summary: Realize construction photo management and simple surveying with LRTK

• FAQ (Frequently Asked Questions)

Why location information is necessary for construction photos

In construction projects, construction photos are taken at each stage of the work and saved for quality control and progress records. Construction photos are not merely records; they are important evidence that proves "when, where, and what work was performed." Photos of foundation parts and buried items (concealed parts) that become invisible after completion are especially valuable sources of information that guarantee structural quality into the future. Therefore, photos require accurate information indicating the shooting location as well as the shooting date and time. If photos include location information, the shooting points can be confirmed on drawings or maps, making it easier for stakeholders to share a common understanding.

Challenges in conventional construction photo management

Traditionally, managing construction photos has been a major burden for site supervisors. Photos are taken with a construction board (chalkboard) or an electronic board in the frame, and details such as "project name," "shooting location," "shooting content," and "date/time" are recorded by handwriting or entry. After shooting, those photos must be organized into folders by trade or shooting location and a ledger must be created, which consumes enormous time and effort. Because this work is done manually, there is also a risk of human error. Mistakes on the board, forgotten photos, or omissions during organization can result in missing necessary records or photos from incorrect locations being used. In addition, if objects or markers indicating the shooting location are not visible in the photo itself, it can become unclear later "where this photo was taken," diminishing the value of the photo as evidential material.

Focusing further on the photos' location information, conventional practice rarely records accurate latitude and longitude. Typical digital cameras and smartphone GPS functions produce errors of about 5–10 m (16.4–32.8 ft), so on large construction sites this accuracy is insufficient to precisely identify "where a photo was taken." For example, a shift of a few meters could result in coordinates being recorded for a different structure than the one shown, and when plotting photos on a map for management, reliability was lacking. Thus, the inability to fully utilize location information has been a key issue in construction photo management.

Benefits of improving location accuracy

So what benefits arise if the accuracy of location information attached to construction photos is improved? First, the reliability of photo data increases dramatically. With high-precision location information, it is possible to objectively prove "at which point on the site a photo was taken," which helps prevent fraud (since electronic data is harder to falsify). When construction managers use photos for explanations, accurate coordinates provide solid backing, enhancing persuasiveness to clients and third parties.

Second, the range of applications for location-tagged photos expands. For example, if photo coordinates are imported into electronic maps or drawing software, shooting points can be plotted and managed on a map. This enables automatic classification of a vast number of construction photos by "when and where they were taken," and makes it easy to search for photos from a specific point later. Especially when combined with electronic board apps or photo management systems, photos can be automatically sorted into designated folders based on entered information and location data at the time of shooting, and the creation of a photo ledger can be completed with the push of a button, realizing significant efficiency improvements.

Moreover, precise location information is compatible with future maintenance and other digital technologies. For example, if photos of buried pipes include accurate coordinates, the precise location can be identified during later excavation work, preventing unnecessary digging. In photogrammetry, which generates 3D models of a site using multiple photos and their location data, the accuracy of shooting positions contributes to improving the overall model accuracy. High-precision location-tagged photos thus serve as foundational data that accelerate site DX (digital transformation) not only for construction records but also for surveying and AR-assisted construction support.

High-precision positioning realized with RTK technology

To dramatically improve the positional accuracy obtainable from smartphones or GPS cameras, it is effective to use a positioning technology called RTK. RTK (Real Time Kinematic) is a technique that corrects GNSS (satellite positioning) errors in real time, reducing positioning errors that were conventionally 5–10 m (16.4–32.8 ft) down to a few centimeters. Error information is generated based on satellite signals received at a stationary base point and sent as correction data to the mobile receiver, enabling high precision. In Japan, network RTK that uses the Geospatial Information Authority of Japan’s reference station network and various correction data distribution services has become widespread, making centimeter-level (cm-level) positioning possible without installing a dedicated base station. Also, Japan’s regional quasi-zenith satellite system "Michibiki" provides enhanced positioning signals that can improve accuracy even in mountainous areas where internet communication is difficult. In the past, GNSS receivers capable of centimeter-level positioning were large, expensive, and difficult to handle, but technological advances now allow small, low-cost devices to achieve high-precision positioning, and their use is spreading on ordinary construction sites.

What is the smartphone GNSS device "LRTK"?

Recently, LRTK has emerged as a solution that makes it easier to take advantage of RTK high-precision positioning. LRTK is a compact, lightweight RTK-compatible GNSS receiver device developed by a startup originating from Tokyo Institute of Technology. Pocket-sized, weighing about 125 g and about 13 mm (0.51 in) thick, it attaches to smart devices such as iPhone or iPad by magnet. By pairing with a dedicated smartphone app, correction information is applied to satellite positioning signals in real time, enabling centimeter-level (cm-level) positioning easily anytime and anywhere. LRTK is transforming high-precision surveying, which was traditionally left to specialized equipment and skilled technicians, into something "anyone can do with a smartphone."

When you attach LRTK to a smartphone and launch the app, you can complete on-site position measurement and recording by yourself. For example, you can hold your phone over an inspection point and tap once to immediately obtain and save the latitude, longitude, and height of that point. Combined with the phone’s built-in camera or LiDAR scanner, you can 3D-scan structures and terrain, and with AR features that overlay design drawings or reference point data on the phone screen, one person can accurately set out batter boards and similar tasks. Handling these varied functions in a single device, LRTK is beginning to rewrite on-site norms as a true "all-purpose surveying instrument." Because the device is affordably priced, it can be easily introduced using existing smartphones, and the practice of carrying one device per person on site is realistic.

Achieve centimeter-level location data for construction photos with LRTK

So what changes when LRTK is used for taking construction photos? The main point is that the location information attached to photos becomes dramatically higher in precision. When photos are taken with a smartphone using the LRTK app, centimeter-precision positioning data obtained on-site can be used to automatically tag photo files with latitude, longitude, and altitude. Geotags from conventional GPS that could not be relied upon are transformed into trustworthy positioning tags with LRTK.

Photos with high-precision location tags will revolutionize the workflow of construction photo management. Also, because location data is automatically attached to photos, there is no need to write detailed information on a board in the photo, simplifying on-site shooting. You will no longer need to write the shooting location on a board each time or sort photos later by cross-referencing maps. Since accurate location data is recorded at the time of shooting, it becomes immediately clear "at which location on the site this photo was taken," making subsequent organization and report preparation smoother. In addition, photo data acquired with LRTK can be instantly shared via the cloud. Photos uploaded from the site can be checked in real time by supervisors in the office or remote locations, enabling prompt instructions and corrections.

Efficiency gains from using LRTK

Accurately recording construction photo location information with LRTK contributes not only to improved accuracy but also significantly to workflow efficiency. The main effects are summarized below.

• Significant reduction in working hours: Because surveying and photo shooting can be done simultaneously, processes that were previously performed separately can be consolidated. Waiting for a surveying team for elevation surveys or stakeout, or doing overtime to organize data after shooting, can be reduced, contributing to shorter construction periods.

• Labor savings and response to labor shortages: With a smartphone and LRTK, site staff can complete location measurement and recording without relying on specially qualified surveyors. The ease of providing one device per person makes efficient site management possible even with limited personnel.

• Prevention of human error: Automatic tagging of location and time reduces the likelihood of entry mistakes or mix-ups. Forgotten photos can be prevented by displaying checklists or shooting-location maps in the LRTK app, aiming for zero omissions in records.

• Promotion of data use and sharing: High-precision location-tagged photo data can be used directly as materials for electronic deliverables or imported into GIS systems. Uploading to the cloud allows real-time sharing between office and site, enabling remote understanding of site conditions and issuing instructions from afar.

• Low-cost high-precision: LRTK devices are much easier to introduce than large surveying equipment and can leverage existing smartphones, keeping initial costs down. The cost performance that allows site DX to start without purchasing expensive dedicated equipment benefits both large and small projects.

• Improved safety: Surveying and recording can be done non-contact from a safe distance, even for dangerous slopes or high places. Tasks that previously required scaffolding or entry can be measured with LRTK from a safe posture, reducing risks of falls and other accidents for workers.

Summary: Realize construction photo management and simple surveying with LRTK

Construction photos with high-precision location information directly improve quality control and workflow efficiency. The foundation for that is LRTK, which enables centimeter-level positioning with a smartphone. By introducing LRTK, not only will on-site photo management become dramatically smarter, but surveying tasks that used to be left to specialists can be performed easily by anyone as simple surveying. For example, measuring the coordinates of several arbitrary points on-site and immediately checking them against the positions on design drawings can be done with just a smartphone. It is truly an innovative tool that "performs both surveying and recording in one device."

The construction and civil engineering industries are currently pursuing a productivity revolution through digital technologies, supported by government-led i-Construction initiatives. Smart GNSS solutions like LRTK are a concrete means to that end. If you feel there are issues in your site’s construction photo management or surveying efficiency, consider adopting LRTK. LRTK, a strong ally for surveying and construction professionals, should powerfully support your first steps toward on-site DX.

FAQ (Frequently Asked Questions)

Q. Is the GPS built into smartphones insufficiently accurate?

A. While the GPS standard on smartphones can record positions, it generally has errors of several meters. For construction photos to serve as accurate record materials, this accuracy is often insufficient, especially in situations requiring centimeter-level precision such as stakeout or as-built verification. Using an RTK-capable device like LRTK allows you to confidently record location information even in such cases.

Q. What level of positioning accuracy can I get with LRTK?

A. Depending on the environment, in clear conditions with good visibility you can obtain high precision with errors on the order of 2–3 cm (0.8–1.2 in). Considering that conventional GPS had errors on the order of meters, LRTK offers a dramatic improvement in accuracy, enabling precise position records on the order of centimeters.

Q. Is the operation difficult on-site?

A. No, operating LRTK is very simple. Attach the device to your phone and start positioning by following the app’s instructions and pressing a button. No complicated settings or expert knowledge are required, and even those without surveying experience can use it intuitively. Japanese-language support and manuals are also well provided, so you can introduce it with confidence.

Q. Can it be used at sites without internet access?

A. LRTK typically receives correction information via mobile communication or the internet, but there are methods for use even in environments where communication is difficult. It supports high-precision augmentation services distributed from Japan’s quasi-zenith satellite "Michibiki," allowing augmentation signals from satellites to be used to improve accuracy in mountainous areas outside network coverage. Therefore, you can benefit from LRTK even where network connectivity is unstable.

Q. What equipment or terminals are required to use LRTK?

A. Basically, you need an iOS-compatible smartphone or tablet and the LRTK device. It is currently designed for use with iPhone and iPad and is used with a dedicated mounting case for secure attachment. Install the LRTK app and no special equipment or large-scale preparations are required.

Q. Does LRTK make electronic boards unnecessary?

A. The location and date/time information automatically provided by LRTK can replace some of the information traditionally written on boards. However, it remains necessary to record what is shown in the photo (trade or part description). Using an electronic board in combination with LRTK allows you to combine accurate position data from LRTK with descriptive photo information to create richer records. Because the items written on the board will be reduced, shooting tasks will be much more efficient.

Q. Is LRTK useful for photogrammetry?

A. Yes, LRTK is very useful for creating 3D models via photogrammetry. Knowing shooting positions with high precision makes scale and coordinate alignment smoother, allowing you to reduce the number of ground control points (GCP) installed on site. In aerial photogrammetry using drones, obtaining reference point coordinates on the ground with LRTK makes it easier to align the model to the surveying coordinate system during post-processing. High-precision location data directly improves as-built control as well as volume calculations and terrain model accuracy.

Q. Can it position under elevated structures or near buildings?

A. GNSS positioning requires receiving satellite signals from the sky, so accuracy may degrade in environments such as under elevated bridges or in urban canyons between buildings. This is a common challenge for both conventional GPS and RTK, but LRTK can use multiple satellite systems including GLONASS, Galileo, and Michibiki in addition to GPS, enabling as stable positioning as possible in obstructed areas. Even so, where satellite signals are extremely blocked, positioning becomes difficult, so it is recommended to take measurements at points with line of sight to the sky when necessary.