Grid vs Ground

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Grid vs Ground

This topic discusses Grid vs Ground and how TPC helps you reconcile the two.

Grid vs Ground in Coordinates

When you import data or really any time in TPC, you can convert grid coordinates to ground or visa versa. This is a very simple method of scaling points about a base point, and is used by most CAD programs. See Grid vs Ground: Converting Coordinates.

Grid vs Ground in a Traverse

The Traverse View allows you to use distance type to relate grid distances to the distances it displays. So you can work with ground distances in the traverse and TPC will automatically compute grid coordinates. See Grid vs ground: In a Traverse.

Grid vs Ground in a Drawing

When you label lines in a drawing, you can apply a distance factor just like you do in the Traverse View. The traverse drawing settings that are used to draw each traverse include a distance factor. See Grid vs Ground: In a Drawing.

Grid (Theta) Angle in a Drawing

•In any drawing, choose Tools | Drawing Settings and left click the Miscellaneous tab.

•Enter the appropriate Theta angle.

TPC will add the Theta angle to the direction labels for all survey lines in the drawing. If you were to choose a representative Theta value from your survey and enter it here, you would in effect go from displaying grid North to geodetic (true) North.

Grid vs Ground in COGO

When you used COGO in TPC, you can compute using grid distance or ground distance. There are times when you need to use both, so TPC makes both available. See Grid vs Ground: In COGO.

Site Calibration

TPC's Site Calibration automatically computes calibrated coordinates for geodetic points. This in essence, allows you to use two coordinates systems in TPC at the same time.

For example, you can set up your survey to use a State Plane or UTM CRS, but work entirely in the local site (ground) coordinates of a construction project at starting coordinate point 10000/10000. Just tie some project points with your GPS / GNSS equipment, use them to create a calibration and TPC does the rest. Now all the points you tie with your GPS / GNSS equipment will have local site coordinates in TPC. And when you go to stakeout points, TPC just reverses the process, creating the appropriate geodetic position for each local site point you export.

Geoids

TPC supports a number of geoids that it uses to compute elevations from ellipse heights and visa versa. The current geoid model, including None, is displayed in the first field of the Geoid group box.

By default, TPC sets the geoid to None, meaning TPC treats ellipse heights as elevation and visa versa. If however, you select a geoid, TPC automatically starts using that geoid and it's separation from the ellipsoid to compute the geoid undulation, also called geoid height.

•Geodetic points will then compute a corresponding elevation based on the geoid and their ellipsoid height.

•Coordinate points with then compute a corresponding ellipsoid height based on their elevation.

For more information see Geoids.