Datum Query Help

A datum is a mathematical model of the Earth used to calculate coordinates on maps, charts, and survey systems. LAS currently supports 221 datums. Each datum is identified by a LAS datum code and a datum name. Datums are defined by a spheroid and x,y, and z shifts. An spheroid is a mathematical surface used to approximate the Earth's surface and is defined by a semimajor axis and a semiminor axis. Datums usually apply to certain countries or regions.

The datum query program allows you to query on specific fields and displays all datums that match the query. The user can also choose which datum information to have displayed.

Search Criteria

The following fields and options specify search criteria. The lack of a criterion indicates that all values for the corresponding field are valid for the search. If the "Query Selection" option is selected, at least one field must be specified. If the "Display All Datums" option is selected, the search fields will be ignored and all datums will be displayed when the query is submitted.

Datum Name: Search only for datums whose names contain the input text. The user may also use the wildcard character, *.
Datum Code: Search only for the datum with the specified datum code. You can enter any single valid datum code in the range of 100 to 320. Any invalid numeric entry or an entry outside this range will result in an "Invalid datum code" error.
Spheroid Name: Search only for datums defined by the selected spheroid name. The user can select a specific spheroid name from the given list.
Spheroid Code: Search only for datums defined by the specified spheroid code. The user can enter any single valid LAS spheroid code in the range of 0 to 19. Any invalid numeric entry or an entry outside this range will result in an "Invalid spheroid code" error.
Category: Search only for datums with the selected category. The user can select a specific category from the given list.
Query Results: Use the "Query Selection" option to query on the input search criteria. Use the "Display All Datums" option to display all datums when the query is submitted. If the "Display All Datums" option is selected, all other input search criteria is ignored.

Output Format

Use the following options to select the format in which the datum information is displayed.

Datum Name/Code: Display the datum name and code in the following format:
Datum : (Datum Code) Datum Name
Spheroid Information: Display the spheroid information associated with the datum. Spheroid information displayed includes the spheroid code, name, semimajor axis and semiminor axis.
Region: Display the region with which the datum is associated.
Category: Display the datum's category.
Datum Shifts: Display the X shift, Y shift and Z shift.
Display All: Display all information avaliable about the datum. If this option is selected, the other output format options are ignored.

Submitting a query

Once the query fields have been specified and the output format has been selected, the query can be submitted by clicking the "Submit" button. Note that if the "Query Selection" option is specified, the user must specify at least one of the query selection fields. Failure to do so will result in a "No input information to query on" error.