Lidar Scanning & Indoor Mapping - How Does It Work?

When it comes to indoor mapping, getting the initial read of the indoor location correct is absolutely paramount. A single incorrect dimension or miscalculated measurement can render an entire floor’s worth of maps completely unusable, due to the knock-on effect that one incorrect number can have on the rest of the map. This is even more true when an indoor map is intended as a base foundation upon which systems such as indoor positioning, navigation, or geofencing are to be layered on top of, meaning a slight discrepancy between the map and the physical location can result in wildly inaccurate results.

With achieving accurate initial measurements so critical, it’s natural to wonder what the best way of achieving consistent, precise readings of an indoor location is. There are a number of different methods and technologies available today, and in this post we’ll look at one which has experienced an upsurge in interest in recent years; lidar scanning.

What is lidar scanning & how does it work?

‘Lidar’ is an acronym for “Light Detection And Ranging”. It works in a similar way to classic radar systems used on ships, in air traffic control and in military contexts. A signal is beamed out from a transmitter. When this signal hits a solid object, it reflects back and is detected by a receiver. This reflected signal is then processed and used to create an image of the area surrounding the transmitter, complete with a record of the locations, sizes and shapes of solid objects within that area.

Lidar operates similarly, but instead of using radio waves, it uses light (typically infrared, ultraviolet, or visible). By using light (via lasers), lidar is able to achieve more accurate results than radar, producing more detailed and precise images of the area being scanned. However, lidar is also more susceptible to interference and to signals being blocked, meaning that while lidar excels in controlled environments, radar is still the system of choice for many contexts, such as ships looking to detect objects at significant range and through weather systems.

Specifically, lidar ‘scanning’ tends to refer to using a transmitter that is capable of sending lidar signals in multiple directions at once to scan an entire area, instead of just sending a signal in one specific direction. 

How is lidar used in indoor mapping?

As mentioned above, lidar’s advantage over similar technologies such as radar is the degree of accuracy and precision it can achieve under the right conditions. While there are plenty of outdoor uses for lidar - including everything from soil surveys for agricultural purposes through to autonomous driving systems, where scanners are affixed to the front of vehicles and used to detect obstacles - the level of detail it can achieve makes it well suited to mapping indoor locations.

Historically, indoor maps have been based on architectural drawings or files, such as CAD files, which are often created when a building is first built. These files generally required numerous highly precise measurements to be taken manually, which can therefore be subject to human error, as well as being time consuming to put together initially. The appeal of a system like lidar is:

• It can create new indoor map images with little additional input - this is particularly helpful if the original CAD files or architectural drawings of the indoor location have been lost
• If set up correctly, it helps eliminate human error by removing the need for manual calculations and measurements to be taken
• Lidar-based images of indoor locations will also incorporate features not present in many CAD files or architectural drawings - for example, in a workplace, lidar would pick up things such as desks and chairs. This can reduce the amount of time needed to replicate the ‘true’ real world state of an indoor location

Once the lidar scan is complete, the output data can then be used to create a user-facing indoor map - such as a navigation-enabled map of a retail location within a smartphone app, or a kiosk-based map of a large facility such as an airport or sports stadium.

How accurate is a lidar-scanned indoor map?

One of the major selling points of lidar when it comes to indoor mapping applications is its accuracy. The precise accuracy lidar is capable of achieving hinges on several factors:

• The scanner/ lidar technology used - Different scanners are capable of achieving greater levels of precision. That said, even relatively cost effective options - such as the scanners found on various recent models of iPhone - are capable of achieving an absolute accuracy of 1cm when scanning objects with a side length greater than 10cm

• The number of lidar scans taken - Different lidar scanners are capable of very different scan ranges, with most commercial options boasting ranges of between 20 and 70 meters. However, indoor locations with obstructions like walls and pillars will require more scans in order to achieve a truly accurate picture of an indoor location. In general, the more scans taken, the more accurate the map generated will be

• The complexity of the location being scanned - If the indoor location is, for example, a large warehouse with only shelf stacks, then lidar will be able to generate an accurate map with relatively few scans. Conversely, if the location is an airport or workplace with multiple interconnected spaces, corridors, curved rooms, seating areas, obstacles and more, then more scans and effort will be required in order to get a full picture of the indoor location

As a typical estimate however, many lidar scanner manufacturers estimate their systems are able to achieve an accuracy between 5mm and 30mm (3cm). In most indoor mapping contexts, this level of accuracy is more than adequate to create a map upon which a live positioning ‘blue dot’, a navigation system, geofences, or other applications can be layered and strong, precise results achieved.

The main advantages and disadvantages of using lidar for indoor maps

Advantages

• Accuracy - If good quality scanners are used and the scans are performed by an experienced individual or team, then lidar-generated maps can eliminate human error and create indoor maps with an excellent degree of precision
• Speed - In certain contexts (generally large, spacious indoor locations with few obstacles, such as warehouses) then a lidar-based approach to mapping an indoor location can be faster than the alternatives, such as creating CAD files (assuming they don’t already exist) or manually measuring the space

Disadvantages

• Cost - Lidar scanners vary enormously in price, but commercial-grade scanners can often cost close to $1,000 a day to rent or run into the tens of thousands of dollars to buy. Conversely, CAD files can be generated with very inexpensive software. Both manually measuring an indoor location and using a lidar scanner can be considered specialist skills, meaning the cost of paying someone to undertake either task often balances out, leaving lidar as by far the more expensive option in most scenarios
• Lack of map features and points of interest - CAD files tend to denote certain features of an indoor space, such as restrooms, stairwells and elevators, which are important to any location map and play a key role within navigation systems. Though lidar is capable of producing high quality scans which would pick up many of these features, these scans then need to be annotated and marked up before they’re ready to be used for indoor maps. In terms of creating digital maps, it’s arguably more productive to have a basic map with the correct layout annotations applied than a more complex, detailed map that lacks any data labels
• Editability - Indoor layouts change regularly. CAD files are easy to edit and adapt as required, often with a fairly minimal amount of additional measurements. Lidar scans, on the other hand, require extra formatting to be edited, and significant changes to an indoor location may require a complete re-scan of the location, which can incur significant additional cost. In addition to this, there may be some cases when the minute level of accuracy of a lidar scan is actually a hindrance to the editability of a map, compared to a more simple CAD-based solution. For example, if an indoor space is already populated with furniture and other ephemera, a lidar scan will pick all of this up (and may need it removing before an indoor map can be created), whereas a map created from a CAD file or set of manually taken measurements can just ignore non-pertinent items
  
  

What are some alternatives to using lidar?

CAD

As previously mentioned, CAD or other architectural files are popular options to use as the foundations of indoor maps. The majority of modern buildings have them readily available in some form, meaning lower barriers to entry and shorter setup times compared to lidar. They tend to be accurate enough to use for indoor maps as they will cover the major obstacles and dimensions of a building clearly, as well as showing critical features and points of interest, such as restrooms, elevators and more.

The challenge with CAD files is digitizing them, which can be a long, arduous process and, if done manually, is subject to the potential for human error. Fortunately, Pointr have a solution - MapScale®, our AI-powered tool which can ingest, digitize and learn from dozens of CAD files in seconds, offering an accurate, scalable alternative to manually digitizing files. MapScale now digitizes and updates millions of indoor square footage on a regular basis.

Manual measurements

For buildings where no CAD files are available, one of the most common solutions is to manually map the building. This involves a person or a team visiting the site and using tools - sometimes electronic devices such as laser measures, sometimes analogue options - to physically measure up the building’s dimensions. These dimensions can then be used to create a CAD file, or can be inputted directly into some tools to create a digital twin map.

This process tends to be much more cost effective than using a lidar-based system, primarily due to the much lower cost of the tools involved. However, it can be time-consuming and very prone to human error, particularly as many indoor maps can be rendered entirely inaccurate by just one or two critical measurements being wrong. 

Photogrammetry

Photogrammetry is an increasingly popular method of creating digital maps of both indoor and outdoor environments, thanks to ever-increasing scientific and AI capabilities. 

Multiple, overlapping photographs are taken of the location. Based on the overlaps and differences between these two photos, plus data relating to the scale and range from which the photographs were taken, modern photogrammetry software is capable of stitching images together and creating either a 3D or 2D image of the entire space, which can then be used to create an indoor map.

Much like lidar scans (which can be used for photogrammetry), the accuracy of photogrammetry depends on the quality of images, the quality of the equipment, and how skilfully that equipment is operated. Costs are similarly flexible, with some lower cost options and some which can run into the tens of thousands of dollars.

Photogrammetry is more typically used for creating maps and models of large outdoor spaces, in large part because the complexities and costs involved meaning that it’s rarely the optimum choice for indoor locations; in the vast majority of scenarios, the simplicity and cost-effectiveness of CAD files or manual measurements are more than sufficient for the basis of an indoor map.

Conclusion

Lidar scanning has been a tremendous innovation for a variety of mapping purposes, thanks to its precision, speed, and removal of many elements of human error that are present in other mapping methods.

In terms of its efficacy in indoor mapping, while lidar works similarly well in terms of creating a detailed scan of a location (which is ideal for complicated enclosed areas without CAD files, such as mines), in many instances it’s not the most effective choice. The scans lidar generates can actually be too detailed, leaving considerable work to be undertaken before the scan can be digitized and turned into a map. For instance, a lidar scan of a workplace would pick up chairs and desks, which can be helpful but can also move easily, rendering the initial scan inaccurate.  What’s more, the equipment can be extremely expensive, and often requires a specialist to operate it, further increasing the cost. 

With tools such as Pointr’s MapScale® now able to digitize CAD files at vast scale, the traditional barrier to using such architectural files as the basis for digital indoor maps is considerably lower than in the past. MapScale’s ability to convert hundreds of CAD files at a time into maps and its use of AI to learn from the files it’s already seen means producing numerous interactive, beautifully designed maps at once easier than ever, a scalability that makes it the ideal choice for businesses looking to digitize hundreds or thousands of locations at once.