How to Reliably Locate Survey Control Points Buried in Vegetation and Brush | Complete Guide to Solving Surveying Site Problems

At surveying sites, the situation described as "control points are hidden by vegetation or brush and cannot be found" is a common problem that occurs regardless of season or site conditions. Especially in forests, farmland, and land prior to development, control points that could be confirmed during a previous survey are often completely overgrown by vegetation by the next season. If a control point cannot be found, the surveying work itself cannot begin, which can lead to schedule delays and additional costs. In this article, we systematically explain methods to reliably locate control points buried in vegetation and brush, fully resolving this problem faced by field personnel.

At sites where locating control points is difficult, the personnel's effort is sapped and the time that should be devoted to the actual surveying work is reduced. Also, entering the brush without a plan to find control points increases the risk of safety incidents such as bee stings and heatstroke. By mastering efficient and safe search methods, these risks can be greatly reduced.

Table of Contents

• How reference points become buried in brush and their effects

• Pre-survey procedures to increase discovery rate

• Safe methods for removing vegetation in the brush

• Tools and equipment that help ensure reliable discovery

• Common mistakes that lead to search failures and countermeasures

• How to reliably tackle vegetation-covered sites with high-precision GNSS equipment

How Survey Control Points Become Overgrown by Vegetation and Their Impacts

By understanding how control points become overgrown by brush, you can develop more effective search plans. Control point reference stones and markers are generally placed at locations that facilitate surveying work, but subsequent management varies greatly depending on the region and the managing authority.

National control points (triangulation points and leveling points) are the administrative responsibility of the Geospatial Information Authority of Japan, but actual vegetation maintenance is often entrusted to local collaborators or municipalities, so regional disparities easily arise. Block reference points and multipoint control points established by public surveys are managed by the surveying divisions of municipalities or prefectures, but even where management registers exist, they usually cannot keep up with on‑site vegetation maintenance. Management tends to be deferred especially in less profitable areas and depopulated regions.

Vegetation encroachment progresses in stages. First, annual weeds begin to cover the ground; next, perennials and shrubs take root; and finally tall trees grow thick enough to block even sunlight. In this process, benchmark stones and metal pins at control points become entangled in grass roots and vines, covered by humus and leaf litter, and are rendered almost impossible to visually detect. Even if a control point has been checked in winter, the same location can be overrun in summer by scrub with vegetation heights exceeding 2 m (6.6 ft). Understanding the magnitude of these seasonal changes is critically important when planning work.

The main problems caused by being unable to locate control points buried in undergrowth are delays to surveying work and impacts on precision management. When alternative control points are used, additional work is required to verify their validity. In the worst case, work may have to be suspended because it cannot be carried out to the precision required for design. Additionally, site personnel experience stress from spending time searching for control points instead of progressing with the actual surveying work, which affects on-site morale. In the long term, streamlining control point searches and establishing management systems are increasingly being recognized as industry-wide challenges.

When viewed by type, thickets of herbaceous plants (reed, silvergrass, kudzu, etc.) die back in winter, temporarily improving visibility, but bamboo groves and stands of shrubs obstruct visibility year-round. Also, vines and climbing plants (kudzu, yabukarashi, etc.) entwine around survey markers and are time-consuming to remove. Preparing the most suitable brush-cutting tools for the types of vegetation in advance will make on-site work smoother.

Pre-survey Procedures to Improve Detection Rate

Before conducting on-site exploration, collecting as much information as possible beforehand is the most important factor in increasing the discovery rate. Below, we explain the steps for an effective preliminary investigation.

The first thing to do is collect information using the Geospatial Information Authority of Japan’s Reference Point Results Viewing Service. This service allows you to check information on triangulation points, leveling benchmarks, GNSS reference stations, and other public control points, including coordinate values, elevations, point records, and installation dates. The point records include photos taken at the time of observation and simplified sketches of the surrounding area, allowing partial confirmation of the vegetation conditions at that time. By comparing multiple point records, trends in seasonal vegetation changes also become apparent.

The next step is to assess the current on-site situation using up-to-date satellite imagery. Utilize satellite images from free map services to check the vegetation around the target point in advance. Depending on when aerial photographs were taken, vegetation may appear sparse, but they can be useful for comparison with current conditions. By identifying the extent of bamboo groves and dense forests from satellite images, you can plan on-site search routes in advance. Comparing satellite images from multiple years also allows you to estimate vegetation growth rates.

Furthermore, interviewing surveying contractors or personnel who have previously used the same control point is also effective. If someone who used the control point during the previous fieldwork is nearby, information such as "the vegetation was heavy" or "the reference stone was slightly buried" can be helpful for on-site searches. The knowledge of experienced field personnel is valuable insight not found in digital data. In particular, asking contractors or personnel with multiple past projects about the season-by-season difficulty of searching is especially valuable.

Also, having the person in charge perform a preliminary site inspection (pre-survey) the day before or immediately prior to the work helps streamline the main task. During the pre-survey, they not only check whether control points can be located, but also determine whether vegetation clearing is necessary and what level of equipment will be required. If the pre-survey concludes that vegetation clearing is necessary, completing the clearing before the main work the following day enables smooth surveying operations. Photographs and video recordings taken during the pre-survey are also useful as reference materials for the main work.

Consider interviewing the owners or managers of adjacent land. Farmers who work the fields and local residents may know the recent condition of the reference points. Contacting local agricultural committees or land improvement districts may also provide useful information. In some areas, weed control around reference points is carried out regularly, and such information can be extremely helpful when drawing up work plans.

How to Safely Remove Vegetation in a Thicket

Removing vegetation is an unavoidable task when searching for control points, but unless appropriate methods and safety measures are implemented, it can be hazardous for workers. Working in thickets presents many unexpected dangers, and to prevent injuries thorough preparation and a staged approach to the work is essential.

As basic equipment required for grass-cutting work, long-sleeved shirts and long pants, leather gloves, goggles or a face shield, and work boots (preferably ones that protect the ankles) are recommended. Because the risk of heatstroke is high during summer grass-cutting, be sure to bring a hat, sunscreen, and plenty of drinking water. Also, since hornets and venomous snakes may lurk in the undergrowth, tap the vegetation with a stick before approaching and check your cell phone’s signal coverage in case of an emergency.

Particular caution is necessary during the period when hornets are active (May–November). The sound of a brush cutter can also excite bees, so when working in a group it is desirable that one person act as a lookout to monitor the surroundings. If you are chased by bees, it is important to remain calm, escape the thicket in a low posture, and stop moving until the bees leave. As for venomous snakes, one countermeasure is to plan work to avoid their active times (often early morning and evening).

When removing grass, it is safest and most efficient to begin brush cutting at the outer perimeter and gradually work toward the center. Diving straight into the middle of a thicket can make it difficult to secure an escape route and is dangerous in an emergency. By mowing in a circular pattern from the outside in, you can work safely while keeping track of your progress. Also, during brush cutting, always pay attention to your footing and proceed while checking for any risk of slipping or falling.

When woody plants (shrubs and resprouting shoots) are dense, a hand sickle or a brush cutter alone may not be sufficient. Bring pruning shears and a folding saw, and proceed while cutting branches as necessary. If a tree has grown too large, hiring a professional tree service is also an option. When felling a tree, always ensure that no one is in the direction of the fall and keep a safe distance before beginning work.

After mowing, gather the cut grass in one place or clear it away as much as possible so the ground surface can be easily inspected visually. Once the ground is visible, again perform coordinate guidance and a ground survey to locate the reference point. This is also the moment when your efforts to date are rewarded, so it is important to proceed carefully with the verification.

In bamboo groves, cutting with a hand sickle is difficult, so a folding saw or pruning shears are effective. The nodes of bamboo are hard, and thin-bladed tools may chip. Also, bamboo cut ends are sharp and dangerous, so for safety it is important to always lay the cut end on its side or have it face the ground. If the bamboo roots are intricately entangled, plan your work with the understanding that treating each stalk individually will take time.

Tools and Equipment to Aid Reliable Discoveries

There are various tools and equipment for locating reference points hidden by vegetation, with options depending on purpose and budget. Choosing the right tools has a major impact on both the time required and safety.

The most basic tools are the aforementioned grass-cutting tools and a metal rod (or rebar). A metal rod, though simple, is very effective for searching for reference points: by probing the ground you can judge the presence of a marker stone from the feel and the resonant sound. If there is a marker stone you will feel hard concrete or stone and hear a higher-pitched sound; if it’s soil you will feel softness and hear a dull sound. Metal rods about 400-600 mm (15.75-23.62 in) in length are convenient for the rod itself or for use as a hammer-type tool, and a pointed tip makes it easier to penetrate the ground. When using a metal rod, systematically probing the ground in a directional pattern allows you to pinpoint the marker stone’s location more accurately. With experience, an operator’s ability to distinguish a marker stone from soil by touch alone improves.

Next, metal detectors are effective. They are particularly useful when searching for metal survey markers (metal tacks and metal markers); some models can detect them when buried about 10-20 cm (3.9-7.9 in) below the surface. If kept on-site for construction surveying, they can be used not only for locating benchmarks but also for checking buried pipes and old stakes. When choosing a metal detector, confirm its underground detection depth and detection accuracy, and select one suited to the site’s conditions. Also, regular calibration and maintenance are important to maintain high detection performance. Becoming familiar with the operating procedures in advance will improve efficiency in the field.

High-precision GNSS devices are very effective for narrowing search areas. By using the guidance function to known coordinates, you can approach reference point positions with centimeter-level accuracy (half-inch accuracy), and even in sites where vegetation is dense you can accurately identify target points. If you invest assuming regular use for surveying work, the cost-effectiveness is very high. However, in environments with dense trees radio signals can be blocked and positioning accuracy may decrease, so it is desirable to use them while periodically securing a clear view of the sky. It is also important to check the device’s battery operating time in advance and to plan on-site charging methods and the preparation of spare batteries.

Using aerial photography from drones to get an overview of thicket conditions is also effective. By photographing the area around a reference point with a small drone, you can grasp vegetation density and terrain features that are not apparent from the ground. If there are exposed rocks or man-made objects near the reference point, their positions can sometimes be identified from aerial images. Recording aerial video can also serve as a reference when planning work at a later date. Drone surveys are affected by weather, so it is preferable to operate in the early morning when winds are light. Also, when flying near buildings or power lines, utmost care in safety management is required.

For equipment that is difficult to bring to the site every time, using a rental service before on-site work is also an option. There are providers that offer rental services for high-precision GNSS devices and metal detectors, allowing you to reduce costs for spot use. Renting is particularly efficient for short-term projects. When using rental equipment, carefully verify operating procedures and perform function checks in advance so that the actual work proceeds smoothly.

Common mistakes that cause failures in exploration and countermeasures

Understanding common failure patterns when searching for benchmarks hidden in vegetation will help you avoid making the same mistakes.

The most common mistake is entering the coordinate values incorrectly. Reference point coordinates can be in degrees, minutes, and seconds format or decimal format, and entering the wrong format will point you to a completely different location. After inputting coordinates, always verify the position on the map and visually confirm that it is pointing to the correct location. Establishing a process in which multiple people double-check the coordinate values can help prevent human error.

Another common mistake is making the search area too small. If you don't have a high-precision GNSS, smartphone GPS can have errors of several meters (several ft). Also, if the reference point's coordinates themselves are recorded in a slightly older geodetic datum, they need to be converted to the modern geodetic datum (the World Geodetic System). If you search without converting, you'll end up searching a location tens of meters (tens of ft) away from the actual position. Using automated conversion tools for datum transformations reduces the chance of errors.

Not taking seasonal differences from the previous inspection into account can also cause failure. If a reference point checked in winter cannot be found in summer, it is because changes in vegetation were not anticipated. When searching in summer, you should be prepared to clear a wider area than in winter before checking. Learning the seasonal vegetation growth patterns helps in drawing up efficient work plans.

Additionally, "venturing deep into the brush alone" poses safety risks. Working in a group is ideal, but if you must work alone, always record where you enter and secure a means of communication for emergencies before you start. Venturing into the brush alone with a low smartphone battery can increase the risk of becoming lost. If possible, have a friend wait at the entrance to the brush and check in with each other regularly by radio or mobile phone.

"Performing wide-area clearing without first identifying the search area" can also lead to wasted effort. By first narrowing the search area through coordinate guidance and verifying point records before starting clearing, you can greatly reduce the workload. Avoiding unnecessary clearing also reduces physical exhaustion and allows you to concentrate on surveying work after the reference point is found.

Reliably conquer vegetated field sites with high-precision GNSS equipment

In fieldwork searching for reference points hidden by vegetation, high-precision coordinate guidance is an invaluable ally. This is where high-precision GNSS devices that attach to smartphones come into play.

High-precision GNSS devices use RTK positioning technology, enabling real-time positioning with an accuracy of several centimeters (cm level accuracy (half-inch accuracy)). If you register the coordinates of reference points in the app beforehand, it will accurately guide you to the target point while you look at your smartphone screen, even at sites covered by vegetation. You can start using it simply by attaching a GNSS antenna to your smartphone, and it is also useful for boundary confirmation work in mountainous areas and farmland where bringing large surveying equipment is difficult.

Because it can be operated intuitively like a smartphone, field personnel without specialized surveying qualifications can become proficient in a short period, contributing greatly to labor savings and efficiency improvements. Its high ease of use solves the challenges of the specialized field task of locating control points. You will particularly appreciate the value of the high-precision GNSS guidance function in difficult field work obstructed by undergrowth and vegetation. Additionally, as an alternative when control points cannot be found, leveraging the RTK direct positioning function makes it possible to continue high-precision surveying even without control points. Field personnel who want to simultaneously improve the efficiency and safety of control point searches should consider using high-precision GNSS equipment.

The benefits of introducing high-precision GNSS equipment are not limited to simply reducing the time spent locating reference points. It streamlines the entire surveying workflow and, by enabling solo fieldwork, also allows for optimization of personnel deployment. Because the application automatically performs complex coordinate calculations, calculation errors can be reduced as well. Although there are upfront acquisition costs, in the long term it is an investment that leads to significant operational efficiency gains.

In particular, at sites with control points that are used repeatedly or where surveys are conducted several times a year, the return on investment in high-precision GNSS equipment becomes especially apparent. Once control point coordinates are stored in a database, subsequent retrievals are further streamlined. Furthermore, sharing the same equipment among multiple staff members reduces the acquisition cost burden per person.

In the current surveying industry, improving the efficiency of field work, including searching for control points, has become a very important issue. The combined approach described in this article—pre-survey investigations, safety measures, selecting appropriate tools, and the use of high-precision GNSS equipment—makes it possible to quickly, safely, and reliably locate control points hidden by vegetation. By comprehensively combining these methods, problems at survey sites can be addressed at their root, enabling more efficient and safer operations.