Coordinate Systems: Difference between revisions

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XMS programs work in a single coordinate system. The user selects what system will be used using the [[SMS:SMS Menus|''Edit | Coordinate System'']] menu command.
XMS programs work in a single coordinate system. Using the [[SMS:Edit Menu|''Display'' | '''Display Projection''']] menu command selects what system will be used.


Both a horizontal and vertical system are specified. Many numerical models work in a local system, so there may not be a problem if the user does not know what coordinate system the data is referenced to. If the desired model requires a global system, or the base data is referenced to more than one system, the modeler must determine the coordinate systems involved.
Both a horizontal and vertical system are specified. Many numerical models work in a local system, so there may not be a problem if it is not known what coordinate system the data is referenced to. If the desired model requires a global system, or the base data is referenced to more than one system, the modeler must determine the coordinate systems involved.


Since data can be gathered and referenced to various coordinate systems, XMS  allows the user to convert data from one coordinate system into another. The [[Coordinate Conversions]] page describes how to do this. The available systems and units include:
Since data can be gathered and referenced to various coordinate systems, XMS  allows converting data from one coordinate system into another. The Coordinate Conversions page describes how to do this. The available systems and units include:


==Horizontal System==
==Horizontal System==
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* [[CPP Coordinate System|CPP]]
* [[CPP Coordinate System|CPP]]


''Local'' is the default horizontal and  vertical system. Unless the user desires to convert data to another system, it  is not necessary to change the system from ''Local''.
''Local'' is the default horizontal and  vertical system. Unless desiring to convert data to another system, it  is not necessary to change the system from ''Local''.


===Horizontal Units===
===Horizontal Units===
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The supported vertical options are for North America. If a non-NAD/HPGN horizontal system is selected, this option is disabled.
The supported vertical options are for North America. If a non-NAD/HPGN horizontal system is selected, this option is disabled.


* '''Local'''
; Local : A system defined for a survey that may or may not relate to a global coordinate system. For more information, see [[Local Coordinate System]]
<blockquote>
; NGVD 29 : NGVD 29 (The National Geodetic Vertical Datum of 1929) is a vertical geodetic  datum formerly called "Sea Level Datum of 1929" or "mean sea level". The datum  was found by averaging the sea level over a period of many years at 26 tide  stations along the coasts of the US and Canada. Because it is an average, it  does not represent the local mean sea level at any particular place. Conversion  to NAVD 88 is done by interpolating between data points between the two  data.
A system defined for a survey that may or may not relate to a global coordinate system. For more information, see [[Local Coordinate System]]
; NAVD 88 : NAVD 88 (The North American Vertical Datum of 1988) is a vertical geodetic  datum created in 1991 from measurements in Mexico, the US, and Canada. NAVD 88  was computed due to land distortions over time from the NGVD 29 measurements.  Conversion to NGVD 29 is done by interpolating between data points between the  two data.
</blockquote>
* '''NGVD 29'''
<blockquote>
NGVD 29 (The National Geodetic Vertical Datum of 1929) is a vertical geodetic  datum formerly called "Sea Level Datum of 1929" or "mean sea level". The datum  was found by averaging the sea level over a period of many years at 26 tide  stations along the coasts of the US and Canada. Because it is an average, it  does not represent the local mean sea level at any particular place. Conversion  to NAVD 88 is done by interpolating between data points between the two  data.
</blockquote>
* '''NAVD 88'''
<blockquote>
NAVD 88 (The North American Vertical Datum of 1988) is a vertical geodetic  datum created in 1991 from measurements in Mexico, the US, and Canada. NAVD 88  was computed due to land distortions over time from the NGVD 29 measurements.  Conversion to NGVD 29 is done by interpolating between data points between the  two data.
</blockquote>


===Vertical Units===
===Vertical Units===
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* [[Single Point Conversion]]
* [[Single Point Conversion]]
* [[Coordinate Conversions]]
* [[Coordinate Conversions]]
* [[Projections]]


== External Links ==
== External Links ==
* [http://www.ngs.noaa.gov/corbin/class_description/Tidal_Geodetic_Datums.shtml Introduction to Tidal and Geodetic Vertical Datums and Datum Computations] &ndash; Presentations available [ftp://ftp.ngs.noaa.gov/pub/corbin/datum_training/ here]
* [http://www.ngs.noaa.gov/corbin/class_description/Tidal_Geodetic_Datums.shtml Introduction to Tidal and Geodetic Vertical Datums and Datum Computations] &ndash; Presentations available [ftp://ftp.ngs.noaa.gov/pub/corbin/datum_training/ at ftp.ngs.noaa.gov]




{{Template:Coordinate Systems}}
{{Template:Projections}}


[[Category:Coordinate Systems]]
[[Category:Coordinate Systems]]
[[Category:Equations|C]]
[[Category:Equations|Coordinate]]
[[Category:General Information|C]]
[[Category:General Information|Coordinate]]
[[Category:External Links]]
[[Category:External Links]]
[[Category:Archived]]

Latest revision as of 21:30, 28 March 2022

XMS programs work in a single coordinate system. Using the Display | Display Projection menu command selects what system will be used.

Both a horizontal and vertical system are specified. Many numerical models work in a local system, so there may not be a problem if it is not known what coordinate system the data is referenced to. If the desired model requires a global system, or the base data is referenced to more than one system, the modeler must determine the coordinate systems involved.

Since data can be gathered and referenced to various coordinate systems, XMS allows converting data from one coordinate system into another. The Coordinate Conversions page describes how to do this. The available systems and units include:

Horizontal System

The options to the right of the dialog change as the horizontal system is changed. For example, the hemisphere is required for a Geographic system and a UTM zone is required for a UTM system.

Local is the default horizontal and vertical system. Unless desiring to convert data to another system, it is not necessary to change the system from Local.

Horizontal Units

The horizontal units can be specified for all systems except Geographic, which uses decimal degrees. The units set here are the units used by the models such as RMA2.

  • U.S. Survey Feet
  • International Feet
  • Meters

Ellipsoid

The Ellipsoid options are only available for non-NAD/HPGN/CPP systems. The ellipsoid can be selected for a region of the world. Changing the ellipsoid changes the minor and major radii of the earth, measurements used in performing conversions. To set the radii for an ellipsoid not included in XMS, select the User Defined ellipsoid and a button appears titled Define. Clicking on the button brings up a dialog where the radii are defined. The Major and Minor Radii (a and b, respectively) are defined in meters only. The Minor Radius can be input directly or defined by specifying the ellipsoid flattening (1/f) or eccentricity squared (e2) variables, where

Ellipsiodcoordsys.jpg

Vertical System

The supported vertical options are for North America. If a non-NAD/HPGN horizontal system is selected, this option is disabled.

Local
A system defined for a survey that may or may not relate to a global coordinate system. For more information, see Local Coordinate System
NGVD 29
NGVD 29 (The National Geodetic Vertical Datum of 1929) is a vertical geodetic datum formerly called "Sea Level Datum of 1929" or "mean sea level". The datum was found by averaging the sea level over a period of many years at 26 tide stations along the coasts of the US and Canada. Because it is an average, it does not represent the local mean sea level at any particular place. Conversion to NAVD 88 is done by interpolating between data points between the two data.
NAVD 88
NAVD 88 (The North American Vertical Datum of 1988) is a vertical geodetic datum created in 1991 from measurements in Mexico, the US, and Canada. NAVD 88 was computed due to land distortions over time from the NGVD 29 measurements. Conversion to NGVD 29 is done by interpolating between data points between the two data.

Vertical Units

The vertical unit is only used for conversions. Area and volume calculations performed by XMS use the horizontal units.

  • U.S. Survey Feet
  • International Feet
  • Meters

See also

External Links