C OMPONENT Linearly Referenced Location

Putting this all together, to specify the location of a COMPONENT by using at or from/to linearly

referenced locations, the linearly referenced location(s) must be added to COMPONENT. Each

includes a linear element, an LRM, a distance along, and perhaps offsets. Additional information about linear elements, their referents, and LRMs may also have to be added to new COBie spread sheets, especially if, as part of an automated reading of a COBie file, linearly referenced locations need to be translated into locations that use a different LRM or linear

element. A spread sheet that accommodates LINEARELEMENTS would facilitate referential

integrity checking, insuring that any linear element used in a linearly referenced location exists.

3.5.3 Recommendation

ISO 19148 is a very comprehensive standard for linear referencing. Based on a well- documented, theoretical model, it is quite sound. But there is no reason to have to support all of its capabilities as a first step, especially since some of these capabilities are optional in the standard.

To simplify the support for linear locations the following recommendations are made:

1. Columns are needed in the COORDINATES spread sheet to specify linearly referenced

locations for each COMPONENT andSPACE/LOCATION. These columns shall be:

a. REFERENCEDCORDINATE – the linear element along which the linearly referenced locations are specified. There is no need to make any simplifying assumption that, if there is to be both from and to linearly referenced locations, they will be along the same linear element. The linear element here is likely to be a reference line, like ELR or LCS entity, so it may be reasonable to assume that assets do not cross linear element boundaries.

If the SPACE spread sheet is generalized to LOCATION, as is proposed above for

geospatial features, then linear elements are LOCATIONS. The COMPONENT

SPACE attribute is synonymous with LOCATION, consistent with geospatial

features and this obviates the need for a separate LINEARELEMENT column. It

also facilitates referential integrity checking of linear elements used in the

COMPONENT spread sheet. The differentiation between feature, geometry, and

edge or component and reference linear element could be accommodated with

the SPACE CATEGORY. If LOCATION is used to specify linear elements, then it will

be mandatory that from and to linearly referenced locations be measured along the same linear element.

b. DISTANCEALONG1 – the distance along the linear element for the first linearly

referenced location, measured either from the start of the linear element or additionally contained referent. This needs to be alphanumeric to be able to support either absolute or relative LRMs. This first location will be for either an “at” or a “from” location value.

c. OFFSET1 – the start offset at the first location. Values will initially be limited to lateral offsets or “n/a” if an offset is not specified. For numeric values, the sign will indicate whether it is to the right or left, based on the positive lateral offset direction specified by the LRM. Supporting alphanumeric values will be needed for Highway Agency XSPs and Network Rail ELR/Track offset requirements. d. Actual data from use case UC 3: Linear Location proposed below may

2. These columns would support the definition of a COMPONENT OR SPACE/LOCATION linearly referenced location equal to either:

a. A point location as a single “at” point An example is the location of a street sign post.

b. A linear location as a curve starting at DISTANCEALONG1, OFFSET1, and ending at

DISTANCEALONG2, OFFSET2, The exact geometry of the curve is not defined in

the COBie file – the two linearly referenced locations merely specify the extent of the curve. An example is curbing.

c. An area location as an area is defined using the top/eft and botton right points

each having a DISTANCEALONG1, OFFSET1 and ending at DISTANCEALONG2,

OFFSET2. The exact geometry of the area is not defined in the COBie file – the

two linearly referenced locations merely specify the extent of the area. An example would be a section of pavement.

3. Add a Facility Attribute for a default Facility LRM. It is highly likely that all Components will be linearly referenced using the same LRM and therefore this can be carried at the Facility level, i.e., specified once per COBie workbook. Alternatively, a Location column or Attribute could be used to specify an LRM of a specific linear element.

4. The definition and details of the LRM can initially be documented in a DOCUMENT or

ATTRIBUTE attached to the FACILITY.

5. Synonyming SPACE to LOCATION would accommodate linear elements as SPACE/

LOCATION NAME attribute of a COMPONENT.

Figure 3: Coordinates expanded to offer actual and/or LRM

One of the use cases proposed below (UC 3: Linear Location) will test if this proposal is a

31 v1.3 October 2013

3.6

Problem 6: Continuous Objects

3.6.1 Problem Identification

Building elements (floor and spaces) and components tend to be discrete entities. With C/I, linear entities are “continuous” – there is no agreement as to where a road for example stops and the next one begins. This is typically based upon each person’s view which includes only a subset of the attributes of the road of interest to that person. The pavement engineer decomposes a road into pavement sections, of uniform pavement type. A traffic engineer may decompose the same road into sections of equal traffic volume, regardless of pavement type. It has been demonstrated that decomposing a road into very small sections based on any of all of its attributes changing value is unreasonable: the resultant sections are too small, redundant information is required since all attributes for all sections must get a value for each resultant section, even if it is unchanged from the previous section, and it is unstable because it is impossible to identify every possible attribute a priori.

It is obviously impossible to tag continuous assets without first establishing a reasonable segmentation scheme. The discretized assets can then be tagged based on an identity established by their physical location limits.

3.6.2 Discussion

The most reasonable solution to continuous entities has proven to be to decompose them based on one (any consistent) reasonable sectioning scheme (intersection to intersection, control section, Engineering Line of Reference (ELR), Location Coding System (LCS) coded section, etc.). It is then possible to define discrete assets as parts of continuous entities by specifying the start and end position of the discretized asset as linearly referenced locations along a reference linear entity. Only then can the resultant discretized assets be tagged.

In COBie, there is an implicit assumption that all COMPONENTS are discrete elements. When one

is referenced by name, the reference is to the COMPONENT in its entirety, for example, a single

pump or door. With C/I, part of the identification of the discretized assets would need to be the start and end location as specified along some pre-stored linear entity. Identifying a section of

track as a single, constructible or manageable COMPONENT requires knowledge about its start

and end delimiting locations. This can be specified using linearly referenced locations along

some reference line (linear element), similar to what was used for locating COMPONENTS above

in Problem 5: COMPONENT Linear Location.

Pavement cross-section can vary across the width of a carriageway as well as along the length

of the carriageway. To specify a pavement section as a single discrete COMPONENT for

construction or maintenance then would require from and to linearly referenced location distance along values as well as from and to offset values for each.

It seems reasonable to combine the notions of locating a COMPONENT with the notion of

delimiting it for discretization for identification sake. So the proposal to add from and to linearly

referenced locations as specified in Problem 5: COMPONENT Linear Location above should

also solve Problem 6: Continuous Objects.

3.6.3 Recommendation