FAQ.Datum&Map

 

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1) How do I create a transformation in Datum & Map?

See SKI-Pro General FAQ #1 above to install the manual PDF files if they haven't been installed already, then:

* Select the User Manual / Getting Started with SKI-Pro topic.

* Select Lesson 5, Calculating Transformation Parameters.

Notes to Page 57:

1. If you are doing a one-step transformation and the local coordinates do not appear in the upper right section:

* Right-click on the screen

* Select Configuration

* Change the transformation type to One-step.

2. To remove a point from the match, uncheck the box to the left of the match pair.

3. To change the match criteria, double-click on Position & Hgt and change to position or height only by double-clicking on the appropriate selection.

 

2) I have 6 points in UTM based on the WGS-84 ellipsoid, and the same 6 points in UTM on the PSAD-56 datum. When I choose Classical 3-D, one of the coordinate sets disappears and I'm not able to proceed.

Datum & Map will only use WGS-84 coordinates for System A (the top, or left set of coordinates). The coordinates must be entered as WGS-84 and not converted using a coordinate system. To correct this situation, do the following steps:

* Export the points as geodetic coordinates and ellipsoid heights to a SKI ASCII file.

* Import these points to a new project as WGS-84 points and ellipsoid heights.

* Use this new project as System A.

 

3) I calculated my average combined factor and got modified northings and eastings, but if I enter a new point coordinate, I can't get back to WGS 84.

The modified coordinates created by Ski-Pro are only one-way. In order to fully utilize these coordinates, you must create a coordinate system. You can create the coordinate system using the Datum & Map module or using Determine Coordinate System in the receiver. Do the following:

* Export an ASCII file of Point ID, Modified Northing, Modified Easting, and Ortho Height.

* Import this file into a new project.

* Run the Datum & Map module (or Determine Coordinate System in the receiver) and specify the original project as System A (the top screen).

* Specify the new project as System B (the bottom screen).

* Match the points you want as control.

* Store the results.

You can now attach this coordinate system to your original project and freely use the ground coordinates.

 

4) My control values don't seem to hold when I create a transformation. Why?

When you store the results, do not use the default of "No Distribution". This allows the control points to change. This is like doing an adjustment with constrained rather than fixed control points. Set the distribution to 1/distance as shown in screen below, and your control coordinates will not change. (See also SR530 FAQ #5.)

Distribution of residuals

 

 

 

Copyright(c) 2003 Ellis R. Veatch II. All rights reserved.
ellisv@ellisv.com