Create sections with centre line

You can use this function to take sections of a DTM perpendicular to a centre line string. The string used as the centre line must be open, can have any number of points, and can be of any length. You are prompted to choose the centre line string in Graphics when you run this function.

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

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

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

Field	Description
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 DTM to section
Location	The name and location of the DTM to section.
Object ID	The object number of the DTM to section.
Trisolation ID	The trisolation number of the DTM to section.
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 selected, and from the point selected 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.
Section spacing	The distance between the sections when you choose At each regular interval, for Position sections at.
Define the output layer
Location	The name and location for the section string file.
Coordinates in	Real world: The coordinates of the points in the section strings are in real world coordinates. Section: The coordinates of the points in the section strings are in section coordinates. That is, the Z value of the segments is the offset value of the slice from the start of the centre line segment.

Output

A new layer that contains the sections extracted from the DTM is created and displayed in Graphics.

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
`There are no valid DTMs loaded in Graphics`	There are no valid DTMs loaded in Graphics that can be used to take centre line sections. Load a valid DTM.
`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. 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. 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.