Create sections with centre line

You can use this function to take sections of a DTM, perpendicular to a centreline string. The string used as the centreline must be open, can have any number of points, and can be of any length.

To run this function: Choose Surfaces > DTM file functions > Create sections with centre line, or...

In the Function Chooser, type CL SECTION DTM, and press ENTER.

Fields on the Extract sections from a DTM along a centre line form

Field	Description
Define the DTM to section
Location	The name and location of the DTM you want to section.
Object ID	The object number of the DTM you want to section.
Trisolation ID	The trisolation number of the DTM you want to section.
Define the centre line string
Layer name	Display only. The layer name for the centre line string file.
String number	Display only. The string number of the centre line string in the string file.
Define the section method
Width either side	The distance to either side of the centre line at which sections will be taken.
Position sections at	At each point: Sections are extracted at each point along the centre line string. The orientation of the section is the bisecting ray of the angle between the lines made from the previous point to the point, and from the point to the next point. The points at the beginning and end of the string are perpendicular to the string. At each regular interval: Sections are extracted at each interval along the centre line. You set the interval distance using the Section spacing field, which becomes active when you select this option. The section lines generated are oriented perpendicular to the centre line string.
Define the file to create
Location	The name and location for the section string file.

Output

A new string file that contains the sections extracted from the DTM is created and saved.

The string file contains Y, X, Z, D1, and D2 fields. The Y, X, Z columns contain section data:

Y - contains the elevation
X - contains the offset from the centre line string,
Z - contains the distance from the start of the string to the point where the section crosses the centre line string

The description fields contain real world coordinate data:

D1 - contains the NORTHING for each point
D2 - contains the EASTING for each point

The information lets you transform the sections back to real world coordinates for plotting. To transform, use STRING MATHS to swap the fields:

from field	to field
Y	Z
D1	Y
D2	X

When sectioning surfaces created on non-horizontal planes along a centre line, the process is:

The surface and centre line string are transformed so that the plane is horizontal.
The section extraction process proceeds as for a horizontal plane surface.

Troubleshooting

Message	Description
`Too many segments in string - 1 required`	You have selected a string with more than one segment. This is not allowed. Select a string that contains only one segment.
`String XXX is closed - It MUST be open`	You have selected a closed string. This is not allowed. Select an open string.
`Left end of section string nnn is outside the DTM`	The point at the left extremity of the line is outside the DTM. The point is at, or close to, the nnn'th point of the centre line string. You need to either make the section length smaller or the DTM larger.
`Right end of section string nnn is outside the DTM`	The point at the right extremity of the line is outside the DTM. The point is at, or close to, the nnn'th point of the centre line string. You need to either make the section length smaller or the DTM larger.
`The selected DTMs were not created on the same plane.`	The DTMs used must be created on the same plane. Choose different DTMs, recreate the DTMs on the same plane, or transform the data in one of the DTMs to match the plane of the other.