Joe Blecha

Tip of the Week #74 - Create Linestring by Station + Offset

Blog Post created by Joe Blecha on May 3, 2019

Cartesian, grid-based coordinates are widely used as the reference vocabulary for surveyors on many projects, but for road and corridor jobs, (x,y,z) are replaced by (s,o,e) or Station, Offset, Elevation, referencing an existing or proposed alignment to determine project coordinates.  Roadway elements such as stormwater inlets, lighting handholes, and signs are often positioned by station and offset relative to the primary roadway alignment.

 

TBC makes field data prep and position calculation simple by offering the ability to define 2D or 3D linestrings by station and offset relative to an existing alignment (or any other line element, it doesn't have to be an alignment object) in the Create Linestring command.   

 

Take the storm water plans and schedule for a new sub-division as shown below:

 

 

The manholes and curb and gutter inlets are referenced to the Twelve Oaks Court alignment.  Let's use the Create Linestring command to key in a linestring representing the manhole structures at Station 2+21.15 at 30' left and right offset for staking in the field.

 

In TBC, you can georeference the PDF site plan or key-in the alignment from the plan sets:

The Twelve Oaks Court alignment is highlighted.  Now open the Create Linestring command, assign a name and properties to the proposed line as you wish, then change the Start Point > Type to Station/Offset from the drop-down menu.

 

Graphically pick the Twelve Oaks Court alignment that you've keyed-in, enter the Distance along (Station) value per the plan set - 221.15 and the Offset 30 (positive is right, negative is left relative to the alignment's direction).  If you've got elevation information, add it optionally as well.  You can always edit the linestring and add elevation information afterwards.

 

Click the Save button and enter the manhole on the other side of the street, at -30 offset value.  Hit the Close button to end the linestring and you've got a simple line, quickly created, for staking out two manhole locations in the field.

 

 

TBC - From Field to Finish (or in this case, from Finish to Field) with Confidence

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