Tip of the Week #39 - Reproject Surface to a New Plane Definition

By Joseph Blecha posted 05-03-2018 20:28


The projected surfaces feature within TBC 4.10 allows for the creation of a surface with a custom UCS. The custom UCS is defined by a plane definition, which is created from either several presets, or user input. This is different from traditional surface creation, where the surface geometry is tied to the WCS, or world coordinate system. Traditional surface creation can typically only model 2.5D topography, or non-vertical surfaces.


The projected surface geometry is tied to its’ custom UCS, therefore any calculations, comparisons, or reports will also be tied the UCS. This can lead to a few minor pitfalls when trying to compare two projected surfaces.

When trying to compare projected surfaces via a report, or cut/fill map, you may get this error mark:



This means that the surfaces you are trying to compare were not created using the same plane definition. The plane definition creates a local coordinate system which determines how TBC interprets the surface’s geometry. If two surfaces have geometries relative to different coordinate systems, TBC cannot compare them.


This would be like trying to compare two point clouds that are not georeferenced to each other, or trying to compare objects with coordinates generated from different datums.


You can check if surfaces are comparable by checking the projected surface’s projection orientation.To view this, go to the surface’s properties and scroll to the bottom of the pane. You should see a category “Projection Orientation.”



The projection orientation defines the surface’s normal axis. This normal axis is how TBC determines if two surfaces can be compared. The normal of a plane is shown below. The normal is a vector that is perpendicular to the defined plane.


If your surfaces have the same projection orientation, you’re ready to compare them, if not, you need to change one of the surfaces’ orientation by using the reproject surface command, found right next to the create projected surface command.



This command will allow you to rebuild a surface using a different plane definition. That way, you can make the two surfaces you are trying to compare have matching projection orientations.


Once in the command pane, select one of your surfaces that you are trying to compare, and then select the “Plane Definition” option. This is where you can select the plane definition that matches the other surface you are trying to compare. Once the correct plane definition is selected, hit apply.



Now you'll be able to create reports, or cut/fill maps between the surfaces.


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