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Ellipses are used by most Coordinate Reference Systems to model the rotation of the earth. You will use them in TPC and this topic will help you manage them.
Editing the Ellipse Values
If necessary, you can edit the values used to compute the ellipse. These values affect the projected coordinates that are computed from Lat/Long.
•From the Grid Settings dialog or the Transform Coordinates dialog, choose Ellipse.
•Enter the ellipse values you want to use then choose Close.
If you are transforming a survey, the target ellipse values are stored with the survey in the TRV file. All future transformations between grid and geodetic positions will be based on these stored ellipse values.
Changing Ellipses
To change ellipses, pull down the Name list and select the ellipse you want.
Saving Ellipse Changes
To save any changes you’ve made to the ellipse values, choose Save. TPC stores the values under the current ellipse name in the user registry. Any new survey that uses this ellipse will use the changes you saved. Existing surveys have already stored their ellipse values with the survey and will not be affected by the changes you save here.
Adding Ellipses
To add an ellipse, choose New and enter a new ellipse name. TPC copies the values from the current ellipse to this new ellipse and displays them in the Ellipse dialog. Any changes you make to the ellipse values are saved automatically since this is a new ellipse.
Deleting Ellipses
You can delete any of the ellipses you do not plan on using. Simply recall the ellipse from the Name list and choose Delete.
Reading Ellipses from ESRI Projection (PRJ) Files
Beginning with TPC 2024, if you use a prj file to define the CRS for a survey, TPC looks for an ellipse definition in the prj file, and if found, incorporates it into that survey's CRS.
Here is an example of the ellipse in the 103779.prj file.
,SPHEROID["S_GRS_1980_Adj_MN_Sherburne",6378443.325,298.257222100883]],
Related Topics
Coordinate Transformations
Editions
Premium, Professional
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