Raster-to-Vector Conversion for Practical Use: Secrets to Improving Work Efficiency

Many practitioners—such as designers in the construction industry, municipal drawing managers, and surveyors—face a common challenge in handling paper drawings and scanned images. Traditionally, digitizing old paper drawings for use in CAD or GIS required a tremendous amount of time and effort for manual CAD re-entry. However, by utilizing the recently notable "raster-to-vector conversion" (raster-vector conversion) technology, it becomes possible to directly convert paper drawings and image data into vector data and efficiently reuse them.

In recent years, i-Construction promoted by the Ministry of Land, Infrastructure, Transport and Tourism and the acceleration of DX (digital transformation) on construction sites have made digital utilization of drawings an unavoidable issue. In this context, raster-to-vector conversion is attracting attention as a solution that enables advanced reuse of paper drawings.

This article explains concrete ways to apply raster-to-vector conversion in practice to significantly improve work efficiency. We will look sequentially at how it improves reuse of paper drawings and scanned images, reduces CAD input labor, enhances editability through vectorization, and improves integration with GIS systems and sharing with other departments. Finally, we will introduce how using the latest technology, LRTK, enables simple surveying for accuracy verification of vector data after raster-to-vector conversion and guidance at the site via AR (augmented reality).

What is raster-to-vector conversion?

As the name suggests, raster-to-vector conversion converts raster images (data composed of pixels, such as photos and scanned images) into vector data (lines and shapes editable in CAD software, etc.). For example, it is the idea of automatically recreating a scanned raster image of a paper drawing as vector data—lines and shapes—that can be used as CAD drawings for architecture or civil engineering. Traditionally, one had to trace the drawing by hand with CAD using the scanned image as an underlay, but using raster-to-vector conversion technology, software-based automatic processing can efficiently generate drawing data. With recent improvements in scanner performance and advances in image recognition AI, automatic conversion that was once difficult has reached a practical level and its application to work has become realistic.

Dedicated software and services for raster→vector conversion have also appeared; these recognize patterns such as lines, arcs, and text in scanned images and vectorize them. Conversion accuracy depends on the clarity of the original image and the complexity of the drawing, but when conditions are favorable the software can automatically recognize most line segments in a drawing, so users only need minimal work such as fixing small details or unclear parts. Note that converting text and dimension values in drawings is often difficult with OCR (optical character recognition), so textual information usually needs to be re-entered manually after conversion; even so, automatic conversion of line diagrams alone drastically reduces workload.

Also, if you scan at an appropriate resolution and set reference lengths and scale information, the converted drawing will be generated at the correct scale. By performing such preparations in advance, the vector data obtained via raster-to-vector conversion can be used in surveying and design work at the required accuracy.

Reusing paper drawings and scanned images

Even if old paper drawings or past scanned image data are sitting unused within an organization, they can become a squandered asset as they are. By using raster-to-vector conversion, such past assets can be revived as digital data and reused in current work.

For example, when planning a renovation and only old building floor plans remain on paper, raster-to-vector conversion can resurrect them as CAD drawings and incorporate them into new design plans. Road ledger maps or old cadastral maps held by municipalities can be vectorized with raster-to-vector conversion so they can be overlaid on current GIS data for integrated analysis or shared with other departments.

Moreover, raster-to-vector conversion is useful in surveying. For instance, if an old cadastral map obtained from the Legal Affairs Bureau exists only as an image, converting it to vector data makes it easier to overlay it with your own survey results to verify boundary line relationships or calculate areas. Because it allows past survey drawings to be leveraged in new survey plans, raster-to-vector conversion is a powerful tool for surveyors.

In this way, drawings that were merely stored as PDFs or image files can be reborn as editable, workable data through raster-to-vector conversion. Operations such as searching for text within drawings, partially reusing elements, and extracting components become possible, enabling effective use of historical drawing information. In terms of shifting from mere storage to “usable assets,” raster-to-vector conversion of paper drawings can be seen as part of DX (digital transformation) promotion.

Improving efficiency of CAD re-entry work

One major advantage of raster-to-vector conversion is that it can greatly streamline the tedious work of CAD re-entry. Traditionally, converting paper drawings into CAD required staff to trace lines and text one by one over the scanned image as a background. When drawings were large, numerous, or complex, this often consumed a whole day or more.

Using raster-to-vector conversion software, the entire drawing can be vectorized in bulk in a matter of minutes to tens of minutes. Of course, manual fine-tuning and touch-ups for unclear areas are necessary for the conversion result, but with the image of “the machine completes all the drafting,” substantial time savings are possible. In many cases, work time can be reduced to less than half compared to before, relieving staff burden and improving productivity.

Additionally, amid current issues such as labor shortages and reforms to long working hours, there is demand to review drafting processes that relied heavily on manual labor. Introducing raster-to-vector conversion frees staff from tedious tracing work so they can focus on higher-value design tasks.

In real-world cases, many reports indicate that by adopting automation through raster-to-vector conversion, time and cost required for CAD conversion were reduced by more than 30% compared to conventional methods. For example, a CAD conversion project for an electrical equipment drawing achieved approximately 35% cost savings compared to manual work by utilizing raster-to-vector conversion. It is clear that significantly more efficient drawing data generation is possible compared to the era of relying on human labor.

Improved editability through vectorization

Once converted to vector data, the original drawing content can be freely edited. While correcting a single line required image editing software when working with images, vector data allows you to select that line object in CAD and easily delete or move it. Modifying the position of dimension lines or adding new annotations is overwhelmingly easier than redrawing a paper drawing from scratch.

Also, vectorized drawings allow operations by layer and by object, making it easy to extract only the necessary elements and reuse them in other drawings. For example, you can extract only specific equipment piping routes from an architectural floor plan and smoothly reuse them in a new project’s drawing within CAD—something not possible with paper drawings. The high editability unique to vector data increases work flexibility and significantly reduces repetitive effort associated with design changes and drawing revisions.

Furthermore, with vector data, measuring areas and lengths in the software is straightforward. Whereas area aggregation on paper drawings required scale-based calculations, vector data can produce accurate results with a single click. Changes in dimensions or area recalculations due to design changes can be reflected instantly, facilitating smoother deliberation during design and construction phases.

Improved GIS integration and sharing with other departments

Vector data obtained through raster-to-vector conversion is also powerful for integration with GIS and other digital systems. For example, vectorizing road drawings or parcel maps and adding coordinate information allows them to be overlaid on GIS maps. This makes it easy to integrate historical drawing information with current geospatial data for analysis or planning. Also, vector data has small file sizes and does not degrade when scaled, making it suitable for distribution and sharing with other departments.

When sharing drawing data between departments, image formats like JPEG or TIFF may be difficult for recipients to use directly, but vector data in common CAD formats such as DXF or DWG can be opened directly by many software packages. This allows stakeholders across design, construction management, asset management, and other departments to use the same drawing data and extract the information they need. The speed and accuracy of information sharing improve, helping reduce miscommunication.

In addition, vector data is easy to centrally manage in an electronic database. Centralized management of drawing data within an organization—tracking change history and always referring to the latest version—also streamlines drawing management tasks. Utilizing the cloud can facilitate smooth external sharing of drawing information.

Furthermore, electronic delivery of construction deliverables (digital deliverables) is increasingly required. Even if only paper drawings remain, generating CAD data via raster-to-vector conversion makes it easier to prepare the data required for electronic delivery. In the sense of reliably preserving past paper drawings as digital assets, this also contributes to future work efficiency.

Points and cautions when introducing raster-to-vector conversion

When actually incorporating raster-to-vector conversion into operations, there are several points to keep in mind. Tools and services for raster-to-vector conversion are diverse: options include raster drawing auto-trace functions built into CAD software for architecture and civil engineering, specialized conversion software, and conversion services. Choose the best method based on the volume of drawings accumulated in-house, the required accuracy, and your budget. It is also important to test with sample drawings before introduction to understand how much can be automated and which parts will require manual correction.

The quality of the source scanned image also greatly affects results. Scan drawings as clear images at about 300–600 dpi and correct any skew or distortion with image editing software. If the original has a lot of stains or handwriting, adjust thresholds at binarization or perform noise removal to reduce clutter. Faint lines should be clarified by contrast adjustment to improve recognition rates of the conversion engine. Taking a little care to prepare input data is ultimately the quickest way to improve conversion accuracy.

Also, verification and finishing of converted data are indispensable. After the conversion result is output, first measure known dimensions to confirm that the overall drawing scale is correct. If line segments are broken by automatic processing or duplicated lines are detected, delete or correct them appropriately in CAD. Textual information is prone to omission or misrecognition, so re-enter it accurately with reference to the original. Immediately after conversion, all lines are often assigned to a single layer, so organizing layers by part will make downstream editing and management much easier. Although these fine adjustments take some effort, they are still overwhelmingly more efficient than creating everything from scratch by hand in CAD.

When submitting drawings as final deliverables, do not over-rely on data obtained by raster-to-vector conversion; enhance completeness by manual tracing and corrections as necessary. In cases where precision and presentation are strictly required, such as electronic delivery, thoroughly check text and detail shapes to ensure quality before submission.

Expanding post-conversion uses with simple surveying using LRTK

Vector data obtained by raster-to-vector conversion can gain further value through on-site use. One example is accuracy verification of vector data using LRTK (a simplified surveying system equipped with high-precision GNSS). By taking the converted drawing data to the actual site and measuring positions with an LRTK-compatible smartphone, you can immediately compare the coordinates on the drawing with positioning data obtained in the field to check consistency. For example, you can measure on site to verify whether there are errors in the positions of boundary lines or structures on the vector data. Accuracy checks that used to require skilled surveyors can now be easily performed by anyone using LRTK-based simple surveying.

Moreover, combining LRTK with AR (augmented reality) technology enables intuitive on-site use of vector data. By holding up a smartphone screen, drawing lines and points can be superimposed on the real scene based on LRTK’s high-precision position information. Following AR guides such as arrows or virtual stakes displayed on the phone makes it possible for even inexperienced workers to intuitively perform accurate stakeout work. Compared to the traditional method of holding a drawing and measuring with a tape, this enables far more efficient and less error-prone construction management and piling operations. You can also overlay a model of the planned structure onto site footage to compare as-built results and check finishes. Further, AR can visualize positions of underground buried objects known from drawings on the surface, aiding safety checks to avoid damaging pipes during excavation. Combining data obtained from raster-to-vector conversion with LRTK-based AR guidance can realize a new workflow that enhances efficiency and accuracy consistently from drawing digitization to on-site construction.

Thus, raster-to-vector conversion is not limited to mere digitization of drawings but holds the potential to transform overall on-site work processes. By making effective use of paper drawings instead of letting them lie dormant and integrating them with the latest digital technologies, productivity and quality from design to construction can be dramatically improved. Why not take this opportunity to incorporate raster-to-vector conversion into your practice and experience its effects? It’s well worth trying raster-to-vector conversion on part of your existing drawings to confirm its benefits for effective use of paper drawings and work efficiency improvement.