What can contour lines reveal? Smartphone AR ushers in a new era of topographic surveying

Limitations of Conventional Use of Contour Lines

Contour lines are a common means of representing terrain relief on a plane, but simply referring to contour lines on paper drawings or in CAD makes it difficult to grasp the actual terrain. In particular, as the size of the site and the complexity of the terrain increase, it becomes harder to intuitively understand the meaning of the contour interval. On paper drawings, one must mentally reconstruct elevation differences in 3D, which is a burden for field personnel.

Moreover, reading contour maps requires specialized knowledge, which limits their usefulness as explanatory materials for stakeholders such as beginners or clients. A flat map alone makes it hard to convey the gradients and the locations of cuts and fills required for construction work, and there were cases where immediate decisions could not be made on site.

• Gap with the actual site: Contour lines on drawings alone do not give a clear impression of the real terrain. Accurately grasping the locations and heights of features such as valleys and embankments requires experience, and misunderstandings or communication errors can easily occur.

• Time and effort required to read maps: When doing surveying and design with paper maps or 2D CAD, you must examine contour information in detail, which is inefficient. For wide-area sites, it is also necessary to refer to multiple cross-sections and survey documents and combine the information.

• Difficulty in communication: Even when explaining the site while looking at documents, the meaning of contour lines is hard to convey to non-specialists. Reaching agreement with clients, residents, or upper management can sometimes take time.

The Innovation of Visualization with Smartphone AR

By using a smartphone's AR (augmented reality) capabilities, you can overlay contour lines and 3D terrain information onto the live view of the site. This allows terrain information that was previously available only in flat, two-dimensional drawings to be integrated with the landscape before you and understood intuitively.

If digitally generated contour lines and color contour maps are displayed in AR over the site viewed through a smartphone camera, the terrain's elevation differences become vividly apparent. For example, visualizing the slopes of mountains and valleys with color-coded contour lines allows on-site personnel to determine at a glance "what is high and what is low." Moving the smartphone along the contour lines creates a sense of connection with the real terrain, providing an on-site feel that cannot be obtained from conventional drawings alone.

In AR display, by moving the smartphone you can observe the terrain from all directions, allowing you to realistically experience the terrain’s irregularities and changes in visibility. This "visualization" enables faster on-site decision-making and makes it easier for everyone to share a common understanding of the design drawings.

Examples of Use for Construction Decisions, Site Development Review, and Consensus Building

The advantages of checking contour lines on-site with an AR-enabled smartphone are manifold. For example, during the design phase of site development works, you can simulate cut and fill volumes and compare multiple development proposals while viewing the existing terrain in AR. On-site, if the planned contour lines are displayed, construction can proceed while intuitively visualizing the actual excavation locations and fill heights.

It also proves powerful for inspection work during construction and after completion. Variations in as-built shape and slope deviations that are hard to understand from two-dimensional cross-sections and tabular reports can be overlaid and checked on site with smartphone AR using colored contour lines and heat maps. For example, in slope construction you can hold up your smartphone on the spot to check whether the design slope has been achieved. For paving and excavation, you can project a color contour map created from post-construction 3D point cloud data onto the site with AR and grasp the difference between the "planned elevation" and the "actual elevation" on the spot.

Furthermore, AR imagery is also useful as explanatory materials and as a tool for building consensus. Showing clients and residents AR-augmented terrain on a smartphone or tablet screen makes it easier to convey what the work will look like even to those without specialized knowledge. Taking screenshots of AR screens for meeting materials is more visually persuasive than traditional paper drawings and helps explanations of construction plans proceed more smoothly.

Align contour lines using high-precision positioning (RTK/LRTK) and point cloud data

To accurately overlay contour lines in AR displays, it is essential to know the smartphone’s position and orientation with high precision. This is where GNSS RTK positioning technology is used. By connecting an RTK-capable high-precision receiver to a smartphone, you can obtain position information far more accurate than conventional GPS. Devices like the LRTK Phone can acquire coordinates with centimeter-level precision (inch-level precision). This allows design contour lines overlaid on imagery captured by the smartphone to match the real terrain correctly without any offset.

Also, by using a smartphone’s LiDAR or photogrammetry functions, you can easily obtain 3D point cloud data of the existing terrain. With a LiDAR-equipped device you can laser-scan slopes and structures, recording the terrain’s undulations as a high-density point cloud. The acquired point cloud is processed in the cloud or with specialized software to generate high-precision mesh models and digital elevation models (DEMs). If contour lines and slope maps created from the DEM are incorporated into a smartphone AR display, you can compare planned and existing contour lines in the same coordinate system. For example, LRTK cloud services include features that automatically generate point clouds and contour lines from smartphone photos, enabling immediate on-site verification while eliminating complex office tasks.

LRTK-based Smartphone Surveying — Practical Workflow for AR Utilization

The workflow for smartphone surveying using LRTK is as follows:

• Surveying and data collection – First, install high-precision GPS control points such as an LRTK Phone at the site, and use a smartphone to capture photos and videos of the surroundings. Because the smartphone app records GNSS positioning data and camera/sensor information simultaneously, you can obtain photos with high-precision location information for each capture.

• Point cloud and mesh generation – The collected photos and LiDAR data are uploaded to the cloud or PC software, where SfM processing and point cloud processing generate a 3D point cloud. A mesh model is constructed from the generated point cloud, and contour lines following the terrain are extracted from it.

• AR visualization – The generated contour lines and mesh data are synchronized to the smartphone app. When you look around the site through the smartphone, contour lines and color contour maps corresponding to the actual terrain are overlaid in real time. This allows you to proceed with work while intuitively confirming differences between planned and existing elevations and the construction extent.

Thus, the key feature is that the entire process—from capture to AR display—can be completed with a single smartphone and the cloud. The need to measure survey points one by one on site and then produce drawings in the office, as in traditional workflows, is eliminated, greatly reducing working time. The LRTK app automatically links photos with location data to organize information and manages it in the cloud on a per-project basis, making it easy to share results and create reports.

Effects and future of smartphone AR surveying

By leveraging smartphones and AR technology, topographic surveying and as-built management are experiencing unprecedented gains in efficiency and sophistication. Field personnel can visualize terrain without specialized equipment, reducing the reliance of surveying work on specific individuals. Because construction decisions can be made instantly on site, the risk of rework and additional costs is also reduced. For example, comparisons of terrain before and after land development and verification of drainage plans can also be carried out quickly using AR.

It is also highly effective for consensus building: using AR displays makes it easier to communicate design intent to stakeholders and to resolve concerns and questions on the spot. Because the LRTK system can share on-site data via cloud integration, another benefit is that confirmations and reports can be made immediately without returning to the office.

At future construction sites, pairing a smartphone with RTK for surveying and management will become the standard. Smartphone surveying with LRTK makes it easy to "visualize" terrain information, including contour lines, and greatly simplifies traditional surveying work. Start by introducing LRTK even on a trial basis and experience the new era of surveying. With LRTK's simple surveying, anyone can obtain highly accurate terrain information using just a single smartphone.