Overview

When importing data into Linear Analytics Services from a file or database using a Data Loading Descriptor (DLD), the DLD must be configured so that Linear Analytics Services knows at what corridor and location each imported entity (whether an asset, event, or survey point) should be placed. The mechanism for doing this is similar for all types of data, and this page explains how to set up a DLD to do this.

Methods of Measurement

If the data to be loaded has location data that is measured as a simple latitude/longitude co-ordinate pair then you can select the "GIS" option when creating your DLD and simply choose which columns in the file contain those co-ordinates. However, if you have data that is measured in a linear fashion along the rail line (or the Linear Analytics Services corridor that represents the rail line) then you need to select the correct method of measurement to use. The methods of measurement that Linear Analytics Services allows are described below.

Corridor Offset

Corridor offset is the simplest method of measurement. It is used when the linear position of the data is measured as a simple offset from the location at which the corridor starts in Linear Analytics Services. It is rare for data coming in from third party software or hardware to be able to use this option, but if data has been pre-processed or previously exported from existing data that is in Linear Analytics Services then it may be used. Using corridor offset is straightforward, in that you just have to specify which column in the file contains the name of the corridor, which column (or columns) in the file contain the actual corridor offset, and what the units are in which that offset is measured.

Marker Offset

Most rail systems measure location using a series of fixed markers. Kilometre posts or mile posts are the most common of these markers, but others are also sometimes used. Assets, events, and other things that need to be located on the railway using a linear location are located using a combination of the named marker and an offset from that marker.

When importing data into Linear Analytics Services from a file, selecting the "Marker Offset" method of measurement will allow you to import data that uses a marker and a linear offset from that marker, with the marker and the offset contained in separate columns. You must select which column in the file contains the corridor name, the marker name, the offset, and the units in which the offset is measured.

Eng. Marker + Fractional Mile

Some rail systems that use markers that have numbers rather than names work out locations based on a relative distance between two markers rather than an offset from a single marker. For example, a railway that uses mile posts as markers and numbers them might indicate the linear location of a point half way between the "mile 21" marker and the "mile 22" marker by referring to it as being at "21.5", or a point a quarter of the way from marker "21" to marker "22" might be referred to as being at "21.25". This is a way of storing both the marker and offset in the same field, and is therefore used by some systems that only have a single field for storage. Note that even though this system is referred to as "Eng. Marker + Fractional Mile", the markers do not have to be a mile apart and therefore the fractional part may represent a fraction of a different distance.

When importing data in this format from a file, you must select the column in the file that contains the corridor name, but only a single column that contains both the marker name and the fractional offset. Because the offset is a fraction of the distance to the following marker rather than a fixed length, it is a scalar quantity (a unitless measure) and therefore there is no need to select what units it is measured in.

Eng. Marker + Offset

Similar to the "Eng. Marker + Fractional Mile" system, this is a method of measurement that combines a marker that has been given a number with an offset in the same field, represented as a whole number with a fractional part. However, the fractional part of the number is not a true fraction. Instead the fractional part represents the offset of the location from the marker in a second unit system. There will be an implied number of decimal places based on how many of the offset unit would normally fit between two markers. For example if the markers are mile posts and the offset is measured in yards (the most common case with this type of measurement) then since there are 1760 yards in a mile there are four implied decimal places in the fractional part of the number. A location of 13.0025 would therefore be 25 yards from mile post (marker) 13. A location of 6.0500 (which in some systems might be erroneously truncated to 6.05 as if it were a true fraction) would indicate a location 500 yards from mile post (marker) 6.

Note that, as with Eng. Marker + Fractional Mile, even if the markers are mile posts they may not be exactly one mile apart. Therefore it is possible that the maximum value for a given marker may not be x.1759. If two markers are slightly closer together the maximum for that stretch of track would be less, and if the markers are slightly further apart then the maximum for that stretch of track would be more. Therefore values such as 33.1765 may be valid locations. When used with mile posts and yards as the offset unit, this format is sometimes referred to as MM.YYYY format.

When importing data in this format from a file, you must specify the column that contains the corridor name, the single column that contains both the marker name and offset, and the units in which the offset is measured.

Track Mapping

In the majority of cases, when data is associated with a particular track rather than being associated with the whole corridor, the track with which each item of data is associated will be stored in a particular column in the data file.

When importing data that has a track column, simply specify that column when creating the DLD.

However, in some cases it is possible that a data set (for example one from an outside source) uses a different naming convention for tracks than the naming convention that is used in your network model. If this is the case then you can use the Track Mapping functionality to make sure that data is associated with the correct track.

Track mapping requires an amount of prior set-up. Before you can use it, you must create or import a set of events on the corridor that are associated with the various tracks in that corridor. Each of these events must have an attribute (the name of the attribute doesn't matter, but it must be the same for all events of this type) containing the name of the track that it is associated with as used in the file. For example, if a track is called "NBMain" in the network model, but called "Northbound" in the file, you need to create one or more events associated with the NBMain track in Linear Analytics Services and make sure that those events have an attribute with the value "Northbound".

When creating the DLD for the data that uses these alternate track names, check the box to enable track mapping, and then supply the category and type of event that you have created and the name of the attribute that contains the alternate track name. You must still select the column in the file that contains this track name as described above.

When Linear Analytics Services loads the data from the file, for each piece of data in the file it will search the corridor at the data's linear location for all events of the correct type, regardless of which track they are associated with. When it finds the event that has an attribute value corresponding to the track name that the data file uses, it will associate the piece of data with the track that is associated with that event.