Lookup Table
This dialog box allows you to view a Lookup Table. It also allows you to open and save lookup table files. To edit a lookup table, you must Save to a file, edit the file in another application (such as MS Word®, MS Excel® or Notepad) and then re-Open the file.
Definition of Lookup Table
A lookup table is a two dimensional (usually) table that allows a computer to find a value, given independent related values. Consider the following example:
A super-elevation lookup table contains cross-fall values as a function of curve radius and design speed. An example table is shown below.
First column is radius (meters)
First row is design speed (km/hr)
Body is Super-elevation value (unitless)
|
|
40
|
50
|
70
|
90
|
|
55
|
0.060
|
|
|
|
|
90
|
0.052
|
0.060
|
|
|
|
190
|
0.037
|
0.046
|
0.060
|
|
|
340
|
0.026
|
0.034
|
0.048
|
0.060
|
|
700
|
0.000
|
0.021
|
0.033
|
0.045
|
|
1500
|
0.000
|
0.000
|
0.024
|
0.033
|
|
3000
|
0.000
|
0.000
|
0.000
|
0.002
|
|
6000
|
0.000
|
0.000
|
0.000
|
0.000
|
|
50000
|
0.000
|
0.000
|
0.000
|
0.000
|
In the lookup table above, a curve of radius 190m with a design speed of 50km/hr will have a super-elevation of 0.046 (4.6%). Note that this table clearly defines a maximum super-elevation of 0.060 (6.0%); for a design speed of 70km/hr, for example, a radius less than 190m is not allowed.
Heading text
The text at the top of the dialog box is a description of the type of table you are viewing; this depends on what you were doing when you opened the Lookup Table dialog box. There are several uses for lookup tables, mostly in horizontal curves.
Lookup Table content
Most of the dialog box is a scrollable window displaying the content of the Lookup Table; this area is not editable (although you may select and copy text to the clipboard).
To edit a lookup table, you must Save to a file, edit the file in another application (such as MS Word®, MS Excel® or Notepad) and then re-Open the file. A lookup table file must be tab or comma delimited. Empty lines or lines with descriptive text must start with a comment character (# or / or ; or : or R or ").
Open (button)
This pops up the File Open dialog box, allowing you to select and open a lookup table file.
Save (button)
This pops up the File Save dialog box, allowing you to save the current lookup table to a file. This file will be tab delimited and any descriptive lines will start with "#". The default file extension is "tbl".
Interpolation (check box)
If this check box is set, values are interpolated (linearly) between the nearest table values. In the table shown above, for example, a curve of radius 700m with a design speed of 55km/hr will have a super-elevation of 0.024 (2.4%).
If this check box is cleared, values are simply the nearest table values. In the table shown above, for example, a curve of radius 700m with a design speed of 55km/hr will have a super-elevation of 0.021 (2.1%).
