Frequently asked QuestionsQ: Can I create my own custom datums within the Geographic Calculator?
Q: Can I create my own custom coordinate systems within the Geographic Calculator?
Q: What format input files can I use?
Q: Has the Geographic Calculator been well tested?
Q: How do I define a NADCON-based datum for Alaska or Hawaii?
Q: Can I integrate Geographic Calculator features into my own application?
Q: Will the Geographic Calculator convert coordinates from NAD27 to NAD83?
Q: Does the Geographic Calculator support the HARN/HPGN datum transformation method? What is the HARN/HPGN method?
Q: What is the NADCON Datum Transformation method? Can I use this method with the Geographic Calculator?
Q: I have a number of Latitude/Longitude coordinates (NAD83), with associated geodetic ellipsoid heights. Can I use the Geographic Calculator to derive MSL height from ellipsoid height?
Q: Which vertical datum transformation method is used by the Geographic Calculator and how accurate is it?
Q: How do I transfer a license from one computer to another?
Q: How do I transfer my floating license from one computer to another?
Q: How do I install and configure my network license for Geographic Calculator 6.3?
Q: Can I create my own custom datums within the Geographic Calculator?
A: Certainly, the Geographic Calculator supports custom datums based on Molodensky, Bursa/Wolfe, NADCON, HPGN/HARN, and the Canadian National Transformation datum transformation methods. You simply need to know the required parameters for your custom datum. The Geographic Calculator provides a simple datum designer that provides an interface for entering the required parameters for your custom datum.
All datum parameters are stored in an external coordinate conversion database, an ASCII file that can be shared between users and different Blue Marble applications.
Q: Can I create my own custom coordinate systems within the Geographic Calculator?
A: Yes, the Geographic Calculator supports custom coordinate systems based on any supported datum, map projection, and unit. The Geographic Calculator provides a simple coordinate system designer that provides an interface for entering the required parameters for your custom coordinate system.
All coordinate system parameters are stored in an external coordinate conversion database, an ASCII file that can be shared between users and different Blue Marble applications.
Q: What format input files can I use?
A: The Geographic Calculator supports point database files in Excel, Lotus, dBase and Text formats. You can also define your own custom ASCII file format. We have defined the SEGP1 file format as a custom file format and ship the definition with the Geographic Calculator as an example of how to define your own ASCII file format.
The Geographic Calculator supports map files in AutoCAD DWG and DXF (R2000 or earlier), MapInfo MIF and TAB (the native MapInfo format), and ESRI Shapefile (the native ArcView format) formats.
Q: Has the Geographic Calculator been well tested?
A: We have invested many person years in testing the coordinate conversion algorithms within the Geographic Calculator. We have also developed relationships with many organizations worldwide who have independently tested the product before deploying it within their businesses. The Geographic Calculator may very well be one of the most significantly tested geographic software applications on the market today!
Q: How do I define a NADCON-based datum for Alaska or Hawaii?
A: We don't ship the required NADCON grid shift files for Alaska and Hawaii with the Geographic Calculator. They are very large. You will need to download the files from our website. Once you have download the Alaska.zip and Hawaii.zip files you need to unzip them in the folder where the coordinate conversion database (geocalc.dat) resides, typically the data folder within the Geographic Calculator installation folder. Once you have downloaded and unzipped the grid shift files into the proper folder you need to use the datum designer in the Geographic Calculator to define a new datum.
Q: Can I integrate Geographic Calculator features into my own application?
A: Yes. Be sure to check out our GeoCalc component. GeoCalc is the underlying coordinate conversion engine within the Geographic Calculator.
Q: Will the Geographic Calculator convert coordinates from NAD27 to NAD83?
A: The Geographic Calculator can use up to 5 different datum transformation methods for this conversion:
- NADCON - the most accurate method for conversions within the U.S. and other territories wherein NADCON grid shift files have been created.
- Canadian National Transformation (NTv2)- the most accurate method for conversions within Canada.
- Bursa/Wolfe - a seven parameter transformation that can be highly accurate if appropriate parameters are used. Generally published parameters will generally yield inferior results to the NADCON or CNT V2 methods.
- MRE - a general polynomial "best-fit" method, not highly recommended unless you have other coordinate data converted using this method.
- Molodensky - a three parameter transformation. Generally published parameters will generally yield inferior results to other methods.
Conversions to and from "enhanced NAD83" (referred to as NAD83/91, HARN, or HPGN on a state-by-state basis in the U.S.) are also supported.
Q: Does the Geographic Calculator support the HARN/HPGN datum transformation method? What is the HARN/HPGN method?
A: Yes. The Geographic Calculator fully supports HARN/HPGN, and uses grid files in a format published and provided by the National Geodetic Survey.
HARN is an acronym for High Accuracy Reference Network, and HPGN is an acronym for High Precision Geodetic Network. These systems are designations used for statewide geodetic network upgrades. HARN is generally used to refer to either system. This upgrade is an improvement to the accuracy of NAD 83 datum, and is most frequently used with the State Plane 1983 Coordinate Group and systems. The HARN datum use GPS (Global Positioning System) observations that are the basis of grid shift files. In GeoCalc, these grid shift files are incorporated in to datum, and referenced during coordinate transformations.
HARNs are being established within the U.S. on a state-by-state basis by the National Geodetic Survey. HARNs have been established for 28 states and Puerto Rico and the Virgin Islands: Alabama, Arizona, California, Colorado, Florida, Idaho-Montana, Kentucky, Louisiana, Maine, Maryland-Delaware, Michigan, Mississippi, Nebraska, New England (CT, VT, MA and RI), New Mexico, Oklahoma, Tennessee, Texas, Virginia, Washington-Oregon, Wisconsin and Wyoming.
You can think of a HARN as a geodetic datum, most easily viewed as an enhanced NAD 83 datum. HARNs are also known as NAD 83/91 and High Precision Grid Networks (HPGN). The NGS HARN method is actually very similar to the NGS NADCON method. As with the NADCON method the shift values for a geographic area are stored in a set of grid files, one representing latitude shifts (named with the extension .las) and one representing longitude shifts (named with the extension .los). The major difference is that the HARN data files contain shifts from NAD 83 to a HARN instead of NAD 27 to NAD 83.
Q: What is the NADCON Datum Transformation method? Can I use this method with the Geographic Calculator?
A: The NADCON method transforms coordinate values between the North American Datum of 1927 (NAD 27) and the North American Datum of 1983 (NAD 83). The National Geodetic Survey (NGS) NADCON method provides a transformation that is accurate to within 0.15-0.5 meters and is highly recommended for NAD27 and NAD83 conversions within the U.S. and other territories. The NGS NADCON method applies a simple interpolation algorithm using a gridded set of standard datum shifts as parameters. The shift values for a geographic area are stored in a set of grid files, one representing latitude shifts (named with the extension .las) and one representing longitude shifts (named with the extension .los). The Geographic Calculator uses grid files in a format published and provided by NGS.
Q: I have a number of Latitude/Longitude coordinates (NAD83), with associated geodetic ellipsoid heights. Can I use the Geographic Calculator to derive MSL height from ellipsoid height?
A: Yes, the Geographic Calculator supports vertical datum conversions from local geodetic ellipsoid (NAD83) height to NAVD88 geoid height, which approximates mean sea level. This specific conversion is implemented using the Geoid 96 model.
Q: Which vertical datum transformation method is used by the Geographic Calculator and how accurate is it?
A: The National Geodetic Survey (NGS) VERTCON method is used to compute the difference in orthometric height between the NAVD29 and NAVD88 vertical datums for a specific latitude and longitude. VERTCON implements predetermined grid shifts (analogous to NADCON horizontal grid shift files) for any particular point on the grid. THIS METHOD IS ONLY VALID IN THE CONTERMINOUS UNITED STATES OF AMERICA FOR CONVERSIONS BETWEEN NGVD29 and NAVD88.
The VERTCON model is accurate to 2 cm (assuming that data collection methods are at least that accurate or better). Since most of the data used to calculate the model fall in the eastern United States, accuracies in that part of the country will tend to be better than elsewhere.
DATA REQUIREMENTS TO USE THE VERTCON VERTICAL DATUM TRANSFORMATION
- Data points must be within the conterminous 48 United States
- Conversion is ONLY valid for conversions between NGVD29 and NAVD88
- Data points must be on the NAD27 or NAD83 horizontal datum for valid transformations
Q: How do I transfer a license from one computer to another?
A: Please consult the License Manager Help for instructions on how to transfer a license. Access this help file from the Help section found on the main menu of the Geographic Calculator.
Q: How do I transfer my floating license from one computer to another?
A: You will find step by step instructions for doing this in our 'Installing and Configuring the Floating License' White Paper found here.
Q: How do I install and configure my network license for Geographic Calculator 6.3?
A: You will find step by step instructions for doing this in our 'Installing and Configuring the Network License for Geographic Calculator Version 6.3' White Paper found here.
| 
