What are orthomosaic images in drone surveying? A simple explanation of 5 uses

When researching drone surveying, one of the terms you often see alongside point clouds and 3D models is "orthophoto." However, even if you've seen the name before, it can be surprisingly difficult to understand how it differs from a regular aerial photograph and how it is used in practice. In particular, clients and site personnel often have questions like "What can it actually be used for?", "Can it be used for drawings or measurements?", and "Which is needed, orthophotos or point clouds?"

Orthophotos are not just visually appealing aerial photographs. They are images corrected and aligned like a map, and are deliverables widely used at construction and civil engineering worksites for understanding current conditions, confirming areas, reviewing plans, construction management, record sharing, and more. A major characteristic is that they combine the clarity of being able to view the entire site at a glance on a single image with the practical ease of use that comes from being based on coordinates.

On the other hand, orthophotos are not foolproof. Because they are not data well suited to representing height, it is important to use them in combination with point clouds and elevation data for tasks such as volume calculations and cross-section checks. In other words, correctly understanding orthophotos also leads to correctly selecting the overall set of deliverables for drone surveying.

This article provides a clear and accessible overview of orthophotos in drone surveying — from the basics and how they differ from regular photographs to conceptual approaches for creating them and common practical applications. It is compiled as material to help decision-making for both those planning to introduce drone surveying and those already using it who want to reassess how they select and use different deliverables.

Table of Contents

• What is an orthophoto in drone surveying

• Differences between orthophotos and regular photographs

• How are orthophotos created?

• Purpose 1: Assessment of current conditions and initial survey

• Use 2: Checking area and distance

• Use 3: Foundation for preparing drawings and reviewing plans

• Use Case 4: Construction progress management and as-built verification

• Use 5 Sharing with stakeholders and record retention

• Precautions when using orthophotos

• The importance of integrating point clouds with high-precision coordinates

• Summary

What is an orthophoto in drone surveying

An orthophoto is an image created by stitching together multiple photographs taken from above and then correcting distortions and tilt so that it is arranged like a map viewed directly from overhead. On site it may be thought of as “a series of aerial photos placed side by side,” but in reality it is a more practical, work-oriented deliverable. Because the photos are not merely joined together but are corrected so that positional relationships are as accurate as possible, it becomes easier to understand the on-site conditions on a flat, two-dimensional plane.

Ordinary photographs are affected by the shooting position, the tilt of the camera, and differences in terrain elevation. For example, the same road can look different in the foreground and background, and buildings can appear to lean. As they are, photographs are difficult to treat like maps or drawings; they may be useful for visual checks, but are not suitable for practical comparisons or measurements.

An orthophoto is an image created by correcting such photographic distortions, reducing positional displacement and making it possible to handle it in a way that closely resembles a plan view. In other words, it may be easier to understand if you think of it as a product transformed from "photos for viewing" into "images for use." Not only is it easy to use as material for explaining current conditions, but the fact that it can be linked to coordinates also makes it much easier to manage in practical work.

Because drone surveying can capture wide areas from the air in a short time, orthophotos are produced for various sites such as large land development sites, roadside areas, slopes, material storage yards, construction yards, farmland, and areas around infrastructure. Since the entire site can be seen in a single image, they are very easy-to-handle deliverables in everyday operations. They are easier to understand than point clouds even without as much specialized knowledge, and the fact that they help create a shared understanding among stakeholders is another reason orthophotos are highly valued.

Furthermore, orthophotos also serve to record the site as it existed at past points in time. Because they can capture on-site conditions that are difficult to convey with text and drawings alone—visually and across a wide area—they provide a large amount of information when reviewed later. Placing orthophotos of the same area side by side for before, during, and after construction also makes it easier to grasp changes. This ability to “preserve information in an easy-to-understand way” is of great value not only for site management but also for internal briefings and sharing with clients.

Differences between orthophotos and regular photographs

What is important to understand about orthophotos is that they are not the same as ordinary aerial photographs. Both are images taken from above, but their purposes and uses differ greatly.

Ordinary photographs are primarily meant for checking appearance. Orthophotos, on the other hand, are intended to understand a site with accurate spatial relationships preserved.

For example, a typical oblique photograph easily conveys the atmosphere and sense of depth of a site, but the scale changes between the foreground and background. Because buildings and trees also appear tilted, they are unsuitable for overlaying on plans or for checking distances and areas. Although they are easy to understand visually, there are limitations when they are used for measuring, comparing, or as explanatory materials.

By contrast, orthophotos are corrected so that the appearance of the entire image is as consistent as possible, allowing them to be used much like a plan view. Of course, no site will ever be completely free of error, but they are far more practical for field work than "visually pleasing photos." They make it easier to check on-site road widths, areas of land development, the placement of temporary structures, and material storage locations within the context of the overall spatial relationships.

Also, while regular photographs capture information one image at a time, an orthophoto compiles multiple photographs into a single product that covers the entire target area. Therefore, another difference is that it represents the site as an area rather than in parts. For on-site personnel, this ability to "grasp the site as an area" is more important than they might imagine. While individual photos alone make oversights and misunderstandings more likely, an orthophoto makes it easier to make assessments that include the relationships with the surrounding area.

However, one important point to note is that orthophotos are essentially images that correct the planar appearance and do not richly represent height information itself. For example, if you want to understand in detail the difference between fill and cut, the slope gradient, or the amount of step changes, point clouds or elevation models are more appropriate. Orthophotos excel at conveying color, shape, and spatial relationships, but for detailed confirmation of elevation differences, other deliverables are better suited.

Understanding this difference makes it easier on-site to decide whether an "orthomosaic image" alone is sufficient or whether a "point cloud" is also necessary. Visible information and measurable information are not necessarily the same. Orthomosaic images are very user-friendly deliverables, but in practice it's important to know how much you can rely on them.

How are orthophotos created?

An orthophoto cannot be produced from a single photograph taken from above. Basically, the target area is captured continuously with overlapping coverage, and the orthophoto is created by analyzing those multiple photographs. Ensuring sufficient overlap makes it easier to estimate the spatial relationships based on the common areas between photos. If there is not enough overlap, seams can appear unnatural and positional corrections can become unstable.

During the image acquisition stage, flight altitude, course settings, shooting direction, shutter interval, and other factors affect the final result. If the altitude is too high, fine details become difficult to see; if it is too low, efficiency drops. If the number of images is insufficient, corrections cannot fully compensate, and conversely, simply increasing the number of images under poor conditions may still fail to achieve the expected quality. In short, orthophotos are not determined solely by post-processing—how they are captured in the field is critically important.

The multiple photos taken are processed afterward to find matching points, calculate the positional relationships between the photos, and align them while estimating the shapes of the terrain and features. Distortions and tilts are then corrected, and the whole is compiled into a single image called an orthophoto. You don’t need to know the technical terms in detail—it's sufficient to think of it as “a map-like image created by aligning many photos according to the site's positional relationships.”

In addition to shooting conditions, the method of alignment is also an important factor affecting final accuracy. By combining approaches such as securing reference points on the ground and leveraging high-precision positioning information, orthophotos can be brought closer to a form that is more useful in practice. If this is left ambiguous, the images may look clean visually but misalignments can become noticeable when overlaid with drawings or existing data.

Also, orthophotos are affected by weather and sunlight. If shadows are too strong, the contours of objects become difficult to read, and puddles or reflections can lead to misinterpretation of surface conditions. Strong winds tend to cause blur and changes in the aircraft's attitude, and subjects that move, such as trees and grass, are prone to causing instability in processing. In other words, orthophotos are not something that can be fully fixed in post-processing; an overall design that includes on-site conditions is an important deliverable.

When you hear it put this way it may seem difficult, but in practice it is important to grasp the basics: "capture the target area with overlap," "be conscious of positional reference points," and "ensure appropriate shooting conditions." Rather than looking at an orthophoto only after it has been produced, understanding how it was created makes it easier to judge whether the deliverable is usable.

Use 1: Assessment of Current Conditions and Initial Survey

The clearest use of an orthophoto is understanding current conditions. Because you can view the entire target area from above without visiting the site, it is extremely useful for initial surveys and preliminary reviews before construction. There are many situations where viewing the whole area in a single orthophoto lets you grasp the situation more quickly and accurately than lining up dozens of on-site photos.

For example, on a proposed development site, it becomes easier to grasp at a glance existing roads, slopes, drainage flow, material storage areas, temporary structures, and how the boundaries with surrounding land appear. Because you can confirm in plan where roads and structures are and what might become obstacles, this also helps organize construction plans and the scope of surveys. If this information is shared before entering the site, the efficiency of on-site inspections will also improve.

Also, in initial surveys the question of "how to explain the site" often becomes an issue. Drawings alone make it hard to convey the site's atmosphere, and photographs alone can make it difficult to understand the spatial relationships. Orthophotos are the deliverable that fills that middle ground. They are visually easy to understand while also making spatial relationships easy to read, so they are useful in internal meetings and in discussions with clients.

A major advantage, especially on sites involving multiple people, is that it can be used like a shared site map. Even if the site staff, design staff, management staff, and the client each focus on different points, basing discussions on the same ortho image makes it easier to reduce gaps in understanding. It becomes less ambiguous what is being pointed to, and conversations such as "this area," "near this slope shoulder," and "along this temporary road" are easier to follow.

Assessing current conditions is the entry point to drone surveying, and if this is unclear it will affect subsequent steps. That is precisely why orthomosaic images are not mere record photographs but are highly valuable as the first operational data linking planning and the field.

Use Case 2: Checking Area and Distance

Orthophotos are also used to check areas and distances. Of course, for precise quantity calculations it may be necessary to cross-check with other data, but they are extremely useful when getting an overview of a site, confirming extents, or carrying out comparative assessments. Because they make it easy to understand extents on a plane, they facilitate a visual understanding of the approximate size of the target area and the extent of each section.

For example, when assessing how far the area usable as a material storage yard extends, how much and where a temporary yard can be secured, or how extensive the areas requiring pavement repair are, orthophotos make it easier to judge. Simply walking the site to check can lead to oversights or differences in perception, but a planimetric image from above allows you to grasp the whole as a coherent unit.

The same applies when verifying distances. Orthophotos are effective for grasping the sense of length along roads, the spacing between facilities, the clearances near boundaries, and the lengths of temporary access routes. Especially when comparing multiple candidates, the ability to judge within the same visual context—rather than by words or intuition—is particularly valuable.

However, it should not be misunderstood that orthophotos alone can provide unlimited measurement accuracy. If imaging conditions or positioning accuracy are insufficient, the images may look fine while the measured values are offset. Therefore, for official quantity calculations or deliverable submissions, you need to confirm that the accuracy requirements are met. Orthophotos are convenient, but it is important to determine what level of measurement they are suitable for.

Even so, in practice orthophotos are extremely valuable in the stages of "first grasping," "narrowing down candidates," and "making explanations easier." Being able to capture the overall framework from a plan-view overview before using a tape measure on site directly translates into faster overall workflow. In terms of streamlining field surveys and accelerating subsequent decisions, orthophotos that can be used to verify areas and distances are a powerful tool.

Use Case 3: Foundation for Drawing Preparation and Planning Review

Orthophotos are often used as a base for creating drawings and for plan review. When you want to proceed while accurately grasping the current conditions, blank drawings or text alone can make it difficult to share a clear image of the site. In such cases, using an orthophoto as the background makes it easier to link the plan’s content to the site’s actual conditions and review it.

For example, routing temporary roads, planning material delivery routes, arranging work yards, delineating construction areas, and organizing inspection target locations are vastly easier when the current site conditions are visible in plan view. Being able to assess how existing structures, obstacles, and boundaries appear on site reduces the risk that desk-based plans will diverge from reality.

Orthophotos are also useful in the preliminary stage before drafting. They make it easier to decide which area to put into the drawings, which parts to detail, and where to place notes or divisions. Rather than jumping straight into producing detailed drawings, organizing while checking the overall outline with orthophotos helps reduce unnecessary rework.

In some sites, the existing drawings do not always fully match the current conditions. Even in such cases, with an orthoimage you can visually confirm where changes have occurred and what the actual on-site conditions are. In situations where relying solely on drawings makes it easy to overlook things or fall into assumptions, referring to an orthoimage makes it easier to make judgments that are closer to reality.

Furthermore, during the planning stage, explanations are often given not only to professionals but also to non-expert stakeholders. In such cases, orthoimages that show current conditions are often easier to understand than drawings consisting only of lines. Because they more clearly convey what is intended to be done and where, they are also effective for internal coordination and preliminary briefings. Orthoimages can be said to serve as an easy-to-use common language for both people who are familiar with the site and those who are not.

Use Case 4: Construction Progress Management and As-Built Verification

After construction begins, orthophotos are useful for progress management and as-built verification. By photographing the same area at regular intervals and creating orthophotos, it becomes easier to visually track changes on site. It also makes it easier to organize the site’s condition over time—how far construction has progressed, how material placement has changed, how temporary structures have been relocated, and so on.

In site management, even if you can grasp daily progress on site, it is not easy to retain it in a form that can be explained later. Photos tend to be partial and vary depending on the photographer. On the other hand, orthophotos record the site as a surface, making it easier to grasp the overall situation when reviewing them later. They are easy to use in progress meetings and reporting materials, and the ease of comparing progress is a major advantage.

Even during as-built verification, orthophotos are useful for confirming positions and understanding the extent of work. They are well suited to plan-view checks such as how far the completed areas have expanded, whether the segmentation of zones matches expectations, and whether the layout is consistent with the temporary construction plan. On particularly large sites, it can be hard to grasp overall progress from ground-level viewpoints alone, so aerial plan-view information is effective.

Of course, it can be difficult for orthophotos alone to perform precise height checks or cross‑section inspections of as-built conditions. However, they are extremely effective for visualizing progress, confirming the scope of construction, and reporting to stakeholders. What site management needs is not always detailed three-dimensional analysis. As information to first grasp the whole and decide where to examine in detail, orthophotos are very easy to work with.

Additionally, keeping records during construction contributes to accountability later on. Having materials that can visually show what the condition was at a given point in time makes coordination both inside and outside the company easier. From the standpoint of not just storing construction records but also preserving them in a form that is easy to explain afterwards, orthophotos are deliverables with high practical value.

Use 5: Sharing with stakeholders and record preservation

Orthophotos are deliverables that are easy for people who are not familiar with a site to understand. This characteristic is a significant advantage when sharing information with stakeholders and preserving records. In practice, not only site personnel but also people from management departments, design departments, clients, and partner companies need to share information. In such cases, data that is too technical can easily lead to gaps in understanding.

Point clouds and 3D models are extremely useful, but they can be difficult to work with if you lack the appropriate viewing environment or expertise. In contrast, orthophotos are intuitively easy to understand as a single image and simple to incorporate into shared materials. Their major appeal is that they are easy to use across applications such as briefing meetings, reports, internal review documents, and on-site handover materials.

Orthoimages are also excellent for record preservation. If you save the pre-construction state, the interim state, and the post-construction state separately, it becomes easier to trace the site's changes later. This is because they can preserve information that is difficult to capture in text alone and information that site photos would only capture fragmentarily, by recording it as a continuous surface. Especially for large sites or sites with complex shapes, this value becomes even greater.

Also, as time passes, it becomes increasingly difficult to recall the site conditions at that time. It's even harder when the people involved have changed. In such cases, having orthophotos makes it easy to grasp the situation at a past point in time at a glance. They can be useful for purposes other than the original one, such as handing over to successors, considering additional construction work, and verifying maintenance and management.

Field data isn't valuable only at the moment it's collected. Being able to review it later, share it easily, and link it to other operations is what matters. In that sense, orthophotos are not merely deliverables but a foundation for transforming field information into a form that remains useful over the long term.

Precautions when using orthophotos

Up to this point, orthophotos may seem like very useful deliverables, but there are several caveats when using them. First and foremost, orthophotos are powerful for planar understanding, while they have limitations for detailed comprehension of height and three-dimensional shapes. If you need to examine earth volumes, slopes, or vertical offsets closely, it is more reliable to use them in conjunction with point clouds and elevation data.

Furthermore, poor imaging conditions can make it difficult to judge what is being seen. When shadows are deep, it becomes harder to discern the condition of the ground surface. Water surfaces and mud are susceptible to reflections, and paved or metal surfaces can also appear visually unstable. In areas with dense vegetation, the ground is easily obscured, and it can be difficult to tell whether what is visible is actually the ground.

In sites with many tall objects such as buildings and trees, trying to understand the situation from orthophotos alone can lead to misunderstandings. A plan-view image taken directly from above does not adequately capture three-dimensional overhangs or wall surfaces. In other words, orthophotos are suitable for "getting an overall view," but they are not appropriate for "fully understanding three-dimensional details."

Furthermore, in practice, because they are often used overlaid on existing drawings and other survey results, positional consistency is also important. Even if an orthophoto looks visually neat, if the method of establishing reference control is ambiguous, misalignment can become noticeable when overlaid with other data. Especially when used for design review or as-built verification, it is essential to consider not only whether it “looks” good but also whether the positions actually align.

Therefore, when introducing orthophotos, it is important to first clarify "how much you will rely on this deliverable." Whether you plan to use them for understanding current conditions and creating explanatory materials, for performing rough measurements, or for overlaying and operating them with other data will change the required imaging conditions and the way you think about positional accuracy. Because orthophotos are convenient, it is precisely for that reason that they must be used appropriately according to their intended purpose.

Importance of Combining with Point Clouds and High-Precision Coordinates

Combining orthophotos with point clouds and high-precision coordinate information further enhances their value. Orthophotos excel at conveying color, shape, and extent, but other information is needed to verify height, volume, and cross-sections. Conversely, point clouds are strong at capturing height and geometry but can be difficult for first-time viewers to interpret. By combining the two, it becomes easier to achieve both clear visualization of the site and ease of measurement.

For example, the workflow of confirming how the construction area and current conditions appear with orthophotos and then using point clouds to examine elevation differences and earthwork volumes is highly practical. Being able to switch back and forth between a plan-view understanding from above and three-dimensional inspection increases the accuracy of site understanding. Even in situations where relying on only one of the two would lead to oversights or biased judgments, dividing their roles and using them together allows them to complement each other.

Furthermore, to make orthoimages truly easy to use on-site, a mechanism for aligning positions is important. Even if you capture the site cleanly, if the images do not align with drawings or existing positional information, their practical usefulness will be limited. Conversely, if positional accuracy is taken into account during acquisition and operation, the continuity of tasks—from site inspection, recording, and sharing to simple positioning and comparison—will improve.

In field operations, there are many situations where you not only view deliverables at your desk but also need to verify positions on the actual site. In that sense, creating orthophotos and securing the correct positions in the field are not separate matters. To make use of the acquired data on site, you need to consider not only post-processing after capture but also the ground-based positional reference and operational procedures.

Rather than treating orthophotos as standalone deliverables, connecting them with on-site positioning and point cloud utilization will become increasingly important in drone surveying going forward. Practitioners are expected to adopt a perspective that develops images intended for viewing into data that can be continuously used.

Summary

An orthoimage in drone surveying is an image created from multiple photos taken from the air, with distortions and tilt corrected so that it can be used like a map. It makes positional relationships easier to understand than ordinary aerial photos and is used in a wide range of practical applications such as site condition verification, measurement of area and distance, as a basis for drawing review, progress monitoring, shared documentation, and record preservation.

What matters most for practitioners is that the information is easy to understand not only for experts but for all stakeholders. Because the overall site can be viewed in a single image, orthophotos are valuable deliverables—they are easy to explain, compare, and archive. On the other hand, for tasks such as determining heights, calculating earthwork volumes, or checking cross sections, it is more suitable to combine them with point clouds and elevation data. Understanding the strengths and limitations of orthophotos and using them appropriately is the quickest way to make the most of deliverables without waste.

And to make orthophotos genuinely useful in the field, it is essential to be able to handle positions with proper alignment. If you want to smoothly link drone-acquired data to on-site verification, simple surveying, and point cloud utilization, ground-side position management is also important. LRTK, as an iPhone-mounted high-precision GNSS positioning device, is a system well suited to situations where you want to advance data use while capturing positions on site. The perspective of not simply producing orthophotos and stopping there, but leveraging them as information usable in the field, will become increasingly important in future drone surveying.