2.1 Why Was a new NADCON Developed? |
The new NADCON Version was developed to replace and/or improve functionality of the existing application, significantly improve the user interface, expand support parameters to encompass a broader spectrum of problem types, and provide platform and architectural improvements. |
2.2 What’s New - NADCON Key Features
NADCON maintains previous functionality and adds many new features.
NADCON now uses negative symbols for south latitude and west longitude.
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2.2.1 The Basics· Provides a new interface. · Accepts three types of latitude/longitude coordinate input. · Accepts any valid geographic coordinate in any hemisphere. · Provides a programmable interface. · Is compliant with section 508 of the Rehabilitation Act of 1973. · Allows user control of conversion grid selection. · Provides datum conversions that are easily extensible. · Supports additional input and output data formats. · Maintains conversion integrity of previously available formats. · Maintains user flexibility. · Maintains reporting. 2.2.2 The DetailsThe new NADCON will provide geographic conversion services similar to the previous NADCON application. The new NADCON application not only maintains existing key features, but also adds several new features and product improvements: · Provides a new interface. This version includes a “user-friendly” interface, making the application easier to use, more intuitive, and therefore less prone to error. The command line interface has been eliminated. · Accepts any valid geographic coordinate as long as it falls within a conversion grid. The new application accepts any valid geographic coordinate. Previous versions of NADCON would not accept coordinates with east longitude or south latitude; it was written for use only in the northern and western hemispheres. In the new NADCON, north latitude is positive and south latitude is negative. For longitude, east is positive and west is negative.
· However, shift values will not follow this convention. A westward shift will be positive to be consistent with previous NADCON versions in which shifts are relative to the positive west value. Therefore, a shift from 80.0W to 81.0W would be considered a shift of +1 (even though those numbers could be displayed as -80 and -81.) · Figure 2-1: Graphic Representation of Latitude and Longitude · Accepts three formats of coordinate data points: decimal degrees; degrees/decimal minutes; or degrees/minutes/decimal seconds. · Provides a programmable interface: so that the library of conversion functions is callable from other computer programs. · Is compliant with section 508 of the Rehabilitation Act of 1973: as amended (29 U.S.C. 794d) regarding accessibility and usability of software for individuals with disabilities. · Includes all previously available grids. For a complete list, refer to Available Datum Conversions. · Allows user control of conversion grid selection. The new application performs conversions based on the conversion type selected by the user. The previous application automatically selected the first set of grids that covered an area that included the input point. Since some grids overlap, but have very different shifts (i.e. the Pribilof Islands and Alaska), this occasionally resulted in an incorrect conversion grid file selection. · Provides datum conversions that are easily extensible: requiring only the addition of new grids.
· Supports additional input and output data formats. “ESRI Shapefile” and “ESRI World File” have been added to the available formats. · Maintains conversion integrity of previously available formats. The previous NADCON application accepted data input as geographic coordinate points in one of four formats. The new application numerically reproduces the conversions exactly the same except for the previously noted correction to the handling of the south latitude and west longitude. The four previously available formats are as follows:
- Single geographic point stated as a latitude/longitude pair in traditional degrees, minutes and seconds. - NGS Horizontal Bluebook format. See file bluebook.txt. - Data files in “Free format 1”. See file Free Format Type 1.doc. - Data files in “Free format 2”. See file Free Format Type 2.doc.
· Maintains user flexibility: can be downloaded and run on a stand-alone workstation or accessed via the web. · Maintains and improves reporting. Consistent with the prior application, the new application produces summary reports for the conversion(s). The conversion summary report produced by NADCON adds paging, headers, and page numbers. It is important to note that if there’s only a single point to be converted the report will print the details of the conversion but not a summary page. This is because the mean and standard deviation are not meaningful when there is only one data point.
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2.3 Datums
Many Available Datum Shifts. |
2.3.1 Available Datum ConversionsThe new application provides a large number of datum shifts. For a complete list, as well as pertinent notes, refer to Available Datum Conversions.
2.3.2 Additional Details About the Grid FilesIn 1992, NADCON capability was expanded to include transformations of latitude and longitude coordinate values between NAD 83 (86) and individual state readjustments for High Accuracy Reference Network (HARN) projects. Latitude and longitude conversions from NAD 83 (86) to HARN and from HARN to NAD 83 (86) are computed in the same
manner as those conversions between NAD 27 and NAD 83 (86), but access different grid files. Prior to 1992 HARNs were referred to as High Precision Geodetic Networks (HPGN) and that acronym is used in the grid file designations; the Florida HARN grid files are, for instance, designated flhpgn.las and flhpgn.los.
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