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Prem Rachakonda, Bala Muralikrishnan, Daniel Sawyer

Prem Rachakonda, Bala Muralikrishnan, Daniel Sawyer’s default image


Roles and Responsibilities of NIST in the Development of Documentary Standards

Published: Thursday, October 4, 2018 - 16:02

The National Institute of Standards and Technology (NIST*) is a nonregulatory federal agency of the Department of Commerce and is the national metrology institute of the United States. NIST’s role in the development of voluntary consensus standards (VCS) is rooted in many policy decisions and government directives that happened during the 1980s and 1990s. NIST has been a leader in the development of many standards, including documentary standards,† ever since its founding in 1901.

The Dimensional Metrology Group (DMG) at NIST develops, performs, and delivers measurements, and physical and documentary standards that promote U.S. innovation and industrial competitiveness. NIST DMG has been involved in many standards committees that are a part of the International Organization for Standardization (ISO), American Society for Mechanical Engineering (ASME), and more lately, ASTM. Recently, DMG, along with various other organizations, was involved in the development of an ASTM documentary standard for 3D imaging systems. NIST led the effort and was a major contributor in developing this standard, and this activity led to the publication of the ASTM E3125-17 standard in 2017. This standards development process was systematic per the rules and regulations of ASTM, which in turn enabled a balanced approach that addressed the concerns of stakeholders while maintaining their involvement and establishing a consensus.

This paper describes the basis for NIST’s authority to participate and drive the development of documentary standards. The paper will then describe the role of DMG in the standards development process. This includes some of the technical and procedural challenges faced by the working group that published the ASTM E3125-17 3D imaging standard.

Standards development and adoption by government agencies

Many government agencies have been involved in the development of standards to achieve their organizational missions. The Department of Defense (DoD) was known to have over 21,000 government unique standards (GUS) in use prior to the year 1997.1 In 1994, then Secretary of Defense William J. Perry wrote a policy memorandum, now known as the “Perry Memo.”2,3 This memorandum highlighted the increasing costs of relying on GUS and directs DoD to use non-government performance standards for its procurement process.

The non-government performance standards mentioned in the “Perry Memo” are voluntary consensus standards (VCS) that are developed by standards development organizations (SDOs) using agreed-upon procedures. The next few subsections will detail the history of SDOs, standards development in the United States, and how they shaped the events that transpired before and after the “Perry Memo.”

*Note: The names of the organizations mentioned in this paper varied throughout their history, but will be referred to in this
paper with their current name unless otherwise specified. ASTM International will referred to as ASTM in this paper.

Note: According to ISO, a documentary standard is defined as a document, established by consensus, and approved by a recognized body, that provides, for common and repeated use, rules, guidelines, or characteristics for activities or their results, aimed at the achievement of optimum degree of order in each context.

2.1 Consolidation of the standards development activity in the United States
Prior to the 1900s, there were many organizations like the American Society of Mechanical Engineers (ASME) and ASTM that led the development of standards for the greater good of society. These professional organizations took up the task of addressing various safety and commercial interests of that era. Soon, it became evident that there was a need to coordinate the standards development activities in the United States. In 1918 five engineering societies and three government agencies came together to establish an organization that is known today as the American National Standards Institute (ANSI). The purpose of ANSI’s founding was to coordinate standards development, approve national consensus standards, and halt user confusion on acceptability. The five engineering societies that founded ANSI were the Institute of Electrical and Electronics Engineers (IEEE), the American Institute of Mining and Metallurgical Engineers (AIME), the American Society of Civil Engineers (ASCE), the ASME, and the ASTM. These five societies, which were themselves core members of the United Engineering Society (UES), subsequently invited the U.S. Departments of War, Navy, and Commerce to join them as founders.4 The U.S. Departments of War and Navy eventually became the U.S. DoD; the U.S. Department of Commerce is the parent organization of NIST.

ANSI was founded as a private nonprofit organization and does not develop any standards, but accredits and assesses the competence of the numerous SDOs.5 ANSI also approves individual documentary standards developed by SDOs and designates them as American National Standards (ANS).6 ANS-designated standards undergo additional scrutiny that involves accreditation of consensus procedures, neutral oversight, approval process, appeals process, and procedural audit. These additional requirements generally align with the policies set forth by OMB A-119. However, it is up to the SDO to consider designating an approved standard as an ANS by following ANSI’s procedures. As of 2015, there were more than 240 ANSI-accredited SDOs, over 100,000 VCS published in the United States, and over 11,000 ANS. For example, the ASME Y14.5M-1994 for “Dimensioning and Tolerancing” is designated as an ANS. ANSI also serves as the U.S. national standards body representative to ISO and many other regional and international standards activities.7,8,9

There are hundreds of national and international SDOs around the world. Some examples of SDOs accredited by ANSI are ASTM, ASME, IEEE, and Underwriter Laboratories (UL). In many countries a centralized body drives the standards activities, which typically is that country’s government and is considered a top-down approach. In the United States, the private sector drives the standards development activities, which is considered a bottom-up approach. Many SDOs use VCS development processes that ensure due process, such as requiring openness, balance, appeals, and consensus.

2.2 U.S. government directives
The U.S. Office of Management and Budget (OMB) issued the circular OMB A-119, in 1980, titled “Federal participation in the development and use of voluntary standards,” which was then revised in October 1982. This was considered a groundbreaking policy. The revised circular in 1982 directed federal agencies to participate in SDOs and rely on VCS not just in procurement activities, but also in its regulations. However, the usage of GUS continued, and as of 1996 there were still about 34000 GUS used by the federal government.10

Subsequent to the “Perry Memo” in 1994, the policy on usage of VCS for federal agencies was reviewed. This led to the passing of the National Technology Transfer and Advancement Act of 1995 (NTTAA, public law 104-113).11 The NTTAA incorporated many of the policy directives of OMB A-119 into a law. OMB A-119 underwent three more revisions since the first revision in 1982.12 The 1993 revision13 reflected the U.S. trade obligations, the 1998 revision14 was updated to reflect the requirements of the NTTAA, and the 2016 revision reflected the changes in numerous federal policies, trade obligations, and practices.15

The directive for all the federal agencies, including NIST, to participate in the development and adoption of VCS comes from the NTTAA and OMB A-119. The NTTAA mandates that all federal agencies adopt VCS wherever possible, except where inconsistent with law or impractical, and to avoid the development of GUS. An example of these directives is DoD replacing a government standard, MIL-L-13762 for lead alloy coatings, developed in 1983, with a consensus standard, ASTM-A308 in 1997.16 GUS are still used by the U.S. federal government for safety, security, and specialized military equipment where appropriate. The primary purpose of NTTAA and OMB A-119 was to eliminate the cost of developing GUS and rely on VCS for such needs wherever possible. As of fiscal year 2016, there are only about 70 GUS reported in lieu of existing VCS used by federal government agencies (excluding DoD and the National Aeronautics and Space Administration) since reporting began in 1997.17

There are many more GUS that are presently in use mostly due to the lack of an equivalent VCS, older GUS that have not been replaced by VCS, or GUS developed due to statutory requirements. For example, the Federal Information Processing Standards (FIPS) published by NIST are government standards that are mandated by law, which in its present form address information security-related issues in the federal government.18 Over the years, many FIPS standards were withdrawn,19 and presently only nine FIPS standards are still in use.20 Another example of usage of GUS by a federal agency is the “Fire protection for shipyards” standard used by the Occupational Safety and Health Administration (OSHA) instead of available VCS. According to OSHA, it was determined that there was no single VCS that covered all the topics for its final ruling and warrants the usage of a GUS.17

Though the adoption of VCS is voluntary in nature, VCS can become a law if government agencies adopt them into regulations by a process known as incorporation by reference (IBR). For example, many standards developed by ASTM and UL have been adopted by federal, state, and local governments or codified into law.21 Many VCS documents are not free of charge and the SDOs may hold the copyrights. However, adoption of VCS into regulations through IBR by federal agencies is permitted as long as the standard is “reasonably available” to the interested parties. The criteria for a VCS being “reasonably available” is detailed in the Office of the Federal Register IBR Handbook.22

2.3 Role of the Department of Commerce and NIST
The U.S. Department of Commerce promotes job creation, economic growth, sustainable development, and improved living standards of all Americans by working in partnership with business, universities, and workers.23,24 It accomplishes its mission through direct assistance to businesses and communities; targeted investments in world-class research, science, and technology; and through various programs that foster innovation, entrepreneurship, and competitiveness. NIST is one of the 12 bureaus of DOC, and its mission is to promote U.S. innovation and industrial competitiveness by advancing measurement science, standards, and technology in ways that enhance economic security and improve our quality of life.25 NIST has always been at the forefront of development of documentary standards, but it is not an SDO.‡26 With the emergence of NTTAA and OMB A-119 directives, NIST was also assigned the role of the coordinating standards and conformity assessment activities and reporting government-wide progress annually to OMB.

2.4 NIST Dimensional Metrology Group activities in documentary standards
The Dimensional Metrology Group at NIST has been leading and supporting the development of many documentary standards for over 60 years. DMG works with manufacturers, users, and other stakeholders on committees of various SDOs in this process. A considerable amount of DMG's research and development efforts supports the development of these documentary standards, primarily as part of ISO, ASME, and ASTM. NIST DMG staff also hold leadership positions in about 20 standards committees that are a part of various SDOs, like ASME, ISO, and ASTM. Some of the recent examples of documentary standards led by DMG were the ASME B89 series, ASTM E57, and ISO 10360 series of standards. Examples of documentary standards from these activities include ASME B89.4.19-200627, the ISO 10360-10:2016 standard28 for laser trackers, and the ASTM E3125-17 standard29 for laser scanners.

Background of the ASTM E3125-17 3D imaging standard

The ASTM E3125-17 standard describes the performance evaluation methods for a class of 3D imaging systems called terrestrial laser scanners (TLS). An overview of the ASTM E3125-17 standard was reported by Rachakonda et. al.30 TLS are used in a variety of applications, including reverse engineering, surveying, large-scale assembly, and historical artifact preservation. TLS were investigated at NIST for use in a variety of applications starting in the late 1990s. NIST recognized the potential impact of these instruments in a range of industrial applications and that standards were needed for these class of instruments. Therefore, NIST organized three workshops between 2003 and 2006 that brought together instrument manufacturers, end users, and other organizations to determine the needs and interests of all the stakeholders.31,32 The participants of these workshops agreed that the development of documentary standards would benefit TLS users and would help promote widespread use of the technology.

The process of selecting ASTM as an SDO for 3D imaging standards was also achieved through a consensus process by participants of the NIST workshop in 2006.32 Several SDOs were initially considered, and the choices were narrowed down to two SDOs. These SDOs were sent questionnaires about their standards development process. The responses were then sent to the participants of the workshop, who were asked to vote for an SDO. A clear majority of the participants selected ASTM as the SDO. After this workshop, the ASTM E57 committee was formally established in 2006 to address issues related to 3D imaging systems, such as TLS and optical range cameras.33 This committee presently has multiple subcommittees, as illustrated in figure 1. Each subcommittee may have multiple work items, which when successful are published as documentary standards. As of the writing of this paper, there are eight published standards under E57, including five standards under the E57.02 subcommittee on test methods.34

Note: Only one laboratory of NIST, the Information Technology Laboratory (NIST/ITL), is accredited by ANSI as an SDO and primarily retains this status due to various historical reasons that precede NTTAA.

After establishing the ASTM E57 committee, a working group started work on evaluating the ranging capability of 3D imaging systems, as this was the fundamental measurement of these systems. In 2015, this working group published the ASTM E2938-15 standard for 3D imaging systems to evaluate relative-range.35 The scope of this standard was limited to the relative range because the main source of error was from the range measurement of the instrument.

In 2013, another working group, WK43218, was convened under ASTM E57 to address the volumetric performance of the TLS. This was because both range and angular errors contribute to the instrument errors when any point-to-point distance is measured. This effort was led by DMG staff, who had considerable experience on laser trackers due to their efforts toward ASME B89.4.19-2006 standard.27 Laser trackers and TLS are very similar in construction, and both these instruments were studied extensively by Muralikrishnan et.al.36,37

Figure 1: ASTM organization structure showing published standards under E57.02

NIST’s role in this standards development process was as a facilitator and provider of subject matter expertise on TLS and dimensional metrology instrumentation. In these roles, NIST could not exert any more authority than other stakeholders in influencing the direction of the standard. All the decisions that were taken during this process had to be agreeable to all the stakeholders, and it was NIST’s responsibility to facilitate consensus. NIST DMG staff worked through both technical and procedural hurdles to achieve this task. As part of the ASTM subcommittee, DMG staff found it necessary to consult many of the guidelines and procedures set forth by ASTM to handle many of the issues that cropped up during this process. Some of the issues encountered by the WK43218 working group are described next.

3.1 Stakeholders
Many of the stakeholders that constituted WK43218 were a part of the working group that published ASTM E2938-15. Their objectives remained the same: to standardize the performance evaluation of TLS, but in the entire work volume of the instrument. NIST publicized the activities of this working group at various venues, websites, conferences, and symposia, and invited participants to contribute to this effort. Participants of this working group consisted of national metrology institutes, instrument manufacturers, distributors, end users, and other subject matter experts.

3.2 Technical challenges
There were many technical challenges during the development of the ASTM E3125-17 standard. NIST DMG was uniquely positioned to address these challenges due to its technical expertise, facilities, and resources. Two of the notable hurdles were the availability of artifacts and algorithms to process TLS data. If not chosen appropriately, both the artifact and the algorithms could introduce an error in the performance metrics that would not be representative of the instrument.

Spheres were chosen as ideal targets for this activity for reasons that are detailed in two technical papers.38, 39 The challenge was the availability of commercial spheres that were suitable to be measured both by the instrument under test and the reference instrument. Early on, it was decided that the test procedures at NIST would be using a laser tracker as the reference instrument. Measuring large reference lengths was challenging on stationary CMMs, and laser trackers provided a way to perform in-situ measurements. A variety of artifacts were considered by the ASTM working group; the breakthrough came with the availability of a commercial artifact known as an “integration sphere,” depicted in figure 2. This sphere had a circularity of < 10 µm, and it was designed to be measured by both the TLS and the laser tracker.

Algorithms to process the TLS data were the second major challenge. As increasing amounts of data were being collected, it was observed that sphere datasets were littered with a lot of phantom or spurious points that did not belong to the sphere. The location of these spurious points varied based on the instrument and its ranging technology and had to be excluded. A variety of algorithms were considered for this activity and an algorithm known as the “cone-cylinder algorithm” was developed for this activity. This algorithm resulted in a minimal number of spurious points. The details of these algorithms were reported by Rachakonda et. al.40

Following are some of the other technical challenges that were encountered by this working group:
1. Instrument downtime, due to repair, servicing, or calibration
2. Proprietary nature of instrument’s construction and data format
3. Lack of resources, facilities, equipment, software, and artifacts to independently examine the technical issues by all the stakeholders

Figure 2: Commercial sphere used on the grid

3.3 Procedural challenges

One of the major procedural challenge happened at the start of this activity: It was to define the scope of the standard. This is one of the most common challenges encountered by many working groups that develop documentary standards. The ASTM E2938-15 standard can be used to evaluate any 3D imaging system; however, ASTM E3125-17 limits the standard only for 3D imaging systems that have a spherical coordinate system such as TLS. This was because the TLS error sources were well understood prior to the start of the standards activity.36,37 Based on this work, the scope was limited to using test positions that were sensitive to the instrument error sources. The scope was also limited to the use of reference lengths instead of consistency checks, and the use of targets that have optical and mechanical properties suitable for a TLS to scan the target in its test volume.

A significant procedural challenge that was encountered during this activity was new stakeholders participating in the midst of development of the standard, and stakeholders participating on an intermittent basis. Concerns about the direction of the standard and the requisite time commitment are a couple of factors that affect stakeholder participation. A considerable amount of effort was expended to satisfy stakeholders about the direction of the standard.

One other challenge was negative votes from nonparticipating members of the ASTM E57 subcommittee. For a standard to be approved, it must be voted on by the subcommittee members. ASTM requires responses from about 60 percent of the subcommittee members, and 90 percent of those responses must be in favor for the standard to be approved. All the negative votes had to be addressed per ASTM procedures. The negative votes were discussed at length to determine if they were persuasive, and technical responses were drafted. The recommended changes to the proposed standard were then submitted to the subcommittee for approval. Once approved, the standard had to be re-balloted because some of the changes were substantial and not editorial.

Following are some of the other procedural challenges that were encountered by this working group:
1. Lack of sustained interest from subject matter experts.
2. Long lead times for procurement, instrument repairs, and manuscript publication
3. Organizational budgetary cycles not matching the standards development life cycle


NIST has historically been a leader in supporting the development of many documentary standards. As new market-driven requirements emerge, NIST provides its expertise to both the private industry and the U.S. government in the development of VCS. In this context, this paper describes NIST's role, which is defined by its statutory authority and further set out in the NTTAA and OMB A-119. The paper then describes some of the challenges faced during the development of one VCS, ASTM E3125, that was developed according ASTM rules and regulations.

Commercial equipment and materials may be identified to specify certain procedures. In no case does such identification imply recommendation or endorsement by NIST, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.

The authors would like to thank all the participants of ASTM WK43218 whose contributions made the ASTM E3125-17 a robust documentary standard for TLSs. The authors would also like to thank Geraldine Cheok of the NIST Engineering Laboratory; David Alderman, Mary Donaldson, and Warren Merkel of the NIST Standards Coordination Office; and Michael Hogan of NIST ITL for their helpful discussions, document review, and feedback regarding voluntary consensus standards.

1. M. Donaldson, N. Rioux. “Fifteenth Annual Report on Federal Agency Use of Voluntary Consensus Standards and Conformity Assessment,” NISTIR 7857 https://standards.gov/nttaa/resources/nttaa_ar_2011.pdf (Accessed on 6/6/2018).
2. W. Perry, “A New Way of Doing Business,” June, 1994, https://www.sae.org/standardsdev/military/milperry.htm (Accessed on 6/6/2018).
3. J. Gansler, W. Lucyshyn, “Commercial-off-the-shelf (COTS): Doing it Right,” http://www.dtic.mil/dtic/tr/fulltext/u2/a494143.pdf (Accessed 6/6/2018).
4. History of the American National Standards Institute: https://www.ansi.org/about_ansi/introduction/history?menuid=1 (Accessed on 6/6/2018).
5. Overview of the U.S. Standardization System, Second Edition, 2007, American National Standards Institute, https://share.ansi.org/Shared%20Documents/News%20and%20Publications/Brochures/U.S.%20Standardization%20System-07.pdf (Accessed 6/6/2018).
6. ANSI Essential Requirements: Due process requirements for American National Standards, https://www.ansi.org/essentialrequirements/ (Accessed on 6/6/2018).
7. ISO Programs—Overview: https://www.ansi.org/standards_activities/iso_programs/overview (Accessed on 6/6/2018).
8. NISTIR 8007: A Review of USA Participation in ISO and IEC, http://dx.doi.org/10.6028/NIST.IR.8007 (Accessed on 6/6/2018).
9. MOU between ANSI and NIST, https://share.ansi.org/Shared%20Documents/About%20ANSI/Memoranda%20of%20Understanding/ansinist_mou.pdf (Accessed 6/6/2018).
10. NIST SP 806, 1996 edition: Standards Activities of Organizations in the United States, https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication806e1996.pdf (Accessed 6/6/2018).
11. National Technology Transfer and Advancement Act of 1995, https://www.nist.gov/standardsgov/national-technology-transfer-and-advancement-act-1995.
12. OMB Circular A-119: Federal Participation in the Development and Use of Voluntary Standards (1982 revision): 9.
13. OMB Circular A-119: Federal Participation in the Development and Use of Voluntary Standards (1993 revision), https://clintonwhitehouse1.archives.gov/White_House/EOP/OMB/html/circulars/a119/a119.html (Accessed 6/6/2018).
14. OMB Circular A-119: Federal Participation in the Development and Use of Voluntary Consensus Standards and in Conformity Assessment Activities (1998 revision), https://www.whitehouse.gov/wp-content/uploads/2017/11/Circular-119-1.pdf (Accessed 6/6/2018).
15. OMB Circular A-119: Federal Participation in the Development and Use of Voluntary Consensus Standards and in Conformity Assessment Activities (2016 revision): https://www.nist.gov/sites/default/files/revised_circular_a-119_as_of_01-22-2016.pdf (Accessed on 6/6/2018).
16. Department of Defense Index of Specifications and Standards. Part 2. Numerical Listing, http://www.dtic.mil/docs/citations/ADA273295 (Accessed on 6/6/2018).
17. FY 2016 Government Unique Standards used in Lieu of Voluntary Consensus Standards, https://standards.gov/NTTAA/resources/FY2016_GUSs_used_in_lieu_of_VCSs.pdf (Accessed on 6/6/2018)
18. FIPS Pub 199: Standards for Security Categorization of Federal Information and Information Systems, https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.199.pdf (Accessed on 6/6/2018).
19. Announcing Approval of the Withdrawal of Ten Federal Information Processing Standards, https://csrc.nist.gov/News/2008/Announcing-Approval-of-the-Withdrawal-of-Ten-FIP-S (Accessed on 6/6/2018).
20. Current FIPS, https://www.nist.gov/itl/current-fips (Accessed on 6/6/2018).
21. Safety and Health Regulations for Longshoring—Personal Protective Equipment, https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10493 (Accessed on 6/6/2018).
22. IBR Handbook, 2017, https://www.archives.gov/files/federal-register/write/handbook/ibr.pdf (Accessed on 6/6/2018).
23. The Commerce Mission Statement: http://www.osec.doc.gov/bmi/budget/strtgc/Aintro.pdf (Accessed on 6/6/2018).
24. The Department of Commerce Budget in Brief: http://osec.doc.gov/bmi/Budget/FY14BIB/ENTIREBIB.pdf (Accessed on 6/6/2018).
25. NIST Mission, Vision, Core Competencies, and Core Values, https://www.nist.gov/about-nist/our-organization/mission-vision-values (Accessed on 6/6/2018) 10.
26. ANSI Accreditation of ITL: https://www.nist.gov/itl/ansi-accreditation-itl (Accessed on 6/6/2018).
27. Performance Evaluation of Laser-Based Spherical Coordinate Measurement Systems, https://www.asme.org/products/codes-standards/b89419-2006-performance-evaluation-laserbased (Accessed on 6/6/2018).
28. ISO 10360-10:2016—“Geometrical product specifications (GPS)—Acceptance and reverification tests for coordinate measuring systems (CMS)—Part 10: Laser trackers for measuring point-to-point distances,” https://www.iso.org/standard/56662.html (Accessed on 6/6/2018).
29. ASTM E3125-17 Standard Test Method for Evaluating the Point-to-Point Distance Measurement Performance of Spherical Coordinate 3D Imaging Systems in the Medium Range, ASTM International, West Conshohocken, PA, 2017, https://doi.org/10.1520/E3125-17 (Accessed on 6/6/2018).
30. P. Rachakonda, B. Muralikrishnan, K. Shilling, D. Sawyer, G. Cheok. “An Overview of Activities at NIST Towards the Proposed ASTM E57 3D Imaging System Point-to-point Distance Standard,” Journal of the CMSC, October 2017.
31. Cheok, G., “NISTIR 7266: Proceedings of the 2nd NIST LADAR performance evaluation workshop, March 15–16, 2005,” https://dx.doi.org/10.6028/NIST.IR.7266 (Accessed on 6/6/2018).
32. Cheok, G. “NISTIR 7357: Proceedings of the 3rd NIST workshop on the performance evaluation of 3D imaging systems, March 2–3, 2006,” https://dx.doi.org/10.6028/NIST.IR.7357 (Accessed on 6/6/2018).
33. ASTM E57 Committee on 3D Imaging Systems, https://www.astm.org/COMMITTEE/E57.htm (Accessed on 5/18/2018).
34. ASTM Subcommittee E57.02 on Test Methods, https://www.astm.org/COMMIT/SUBCOMMIT/E5702.htm (Accessed on 5/18/2018).
35. ASTM E2938-15 Standard Test Method for Evaluating the Relative-Range Measurement Performance of 3D Imaging Systems in the Medium Range, ASTM International, West Conshohocken, PA, 2015, https://doi.org/10.1520/E2938-15 (Accessed on 6/6/2018).
36. B. Muralikrishnan, D. Sawyer, et al. “ASME B89.4.19 Performance Evaluation Tests and Geometric Misalignments in Laser Trackers,” Journal of Research (NIST), 114, 21-35 (2009).
37. B. Muralikrishnan, M. Ferrucci, D. Sawyer, et al. “Volumetric performance evaluation of a laser scanner based on geometric error model,” Precision Engineering, 40, pp. 139–150, 2015.
38. Muralikrishnan, B., Shilling, M., Rachakonda, P., Ren, W., Lee, V., Sawyer, D. “Toward the development of a documentary standard for derived-point to derived-point distance performance evaluation of spherical coordinate 3D imaging systems,” Journal of Manufacturing Systems, vol. 37, part 2, Oct. 2015, pp. 550–557 11.
39. Rachakonda, P., Muralikrishnan, B., Shilling, M., Cheok, G., Lee, V., Blackburn, C., Everett, D., Sawyer, D. “Targets for relative range error measurement of 3D imaging systems,” Journal of the CMSC, vol. 12, no. 1, Spring 2017.
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About The Author

Prem Rachakonda, Bala Muralikrishnan, Daniel Sawyer’s default image

Prem Rachakonda, Bala Muralikrishnan, Daniel Sawyer

Prem Rachakonda, Bala Muralikrishnan, and Daniel Sawyer work in the Dimensional Metrology Group of the Engineering Physics Division at the National Institute of Standards and Technology (NIST).