.
Geodesy Class file:
The class file (.cls) contains the physical definitions of the supported
datums and methods for retrieving the desired datum. Normally you need not
use these methods at all as the functions that need the datum dimentions
contain the necessary code to do this. However there is a function you can
call to get the data.
Mapstuff:
Mapstuff is the file that contains all the action. There are routines for
converting Latitude/Longitude to UTM coordinates and UTM Coordinates to
Latitude/Longitude. There are implementations of T. Vincenty's Direct
and Inverse Solution of Geodesics on the Ellipsoid. There are standard
VB data structures called Types that are used throughout Mapstuff.These
Types add order to the calling sequences of most of the routines. All
Types and Routines are public. All the main functions return an error code
of type Integer to flag success or failure. The error codes are constants
in the definition section of the code. The code names all begin with
WIC (for Windsway Instrument Company) and are ALWAYS Capitalized. A fuction
returning WICNOERROR has completed successfully (this does not necessarily
mean that the information returned is meaningful). Any other error code
means something went wrong during the function call. The return codes for
each function are documented in a comment block at the beginning of the
function.
Mapstuff.bas contains the following routine for your use:
ArcCos
ArcSin
ArcTan
ATan2
These four routine simply implement the trigonometric function in a
way that is standard to my way of doing software.
ComputeZone
This function compute the zone data for any UTM zone. It expects a Type
ZoneStruct and populates it with information concerning the UTM zone of
interest. As with all the main functions in Mapstuff.bas, the function
returns an error code of type Integer that signals success or failure.
Given the latitude and longitude of a place, ComputeZone will return
the UTM central longitude of the place along with the zone number and
zone letter of the place.
DegToRad
RadToDeg
DegToRad converts an angle in decimal degrees to radians and RadToDeg
converts an angle in radians to decimal degrees.
DMSToD
DToDMS
DtoDMS converts an angle in decimal degrees to it constituant parts;
degrees, minutes and seconds. These components are returned a a DMS
structure (byref). DMSToD converts an angle from degrees/minutes/seconds
to decimal degrees.
Sex2Deg
Sex2Deg converts an angle expressed in sexigesimal format: dd.mmsssss
where dd is degrees, mm is minutes and sssss represents ss.ssss seconds
into decimal degrees: dd.ddddd
The function assumes that minutes are expressed as two digits and the
first two digits of ss are the whole seconds and the balance of ssssss
are the decimal portion. The decimal portion of ssssss can be expressed
to any reasonable number of places. Therefore dd.mmssssss expresses an
angle of dd degrees mm minutes and ss.ssss seconds
FmtDMS
FmtDMS converts decimal degrees dd.ddddd into a string dd mm ss.ssss
or time expressed as hh.hhhhh into a string hh mm ss.ssss with the
appropriate symbols i.e. 23° 34' 45.5678" or 23h 34m 45.5678s. User
specifies degrees or time and the number of decimal places for seconds.
Decimal range from 0 to 5. If more than 5 places is specified, places
is set to 5. FmtDMS is intended for printing or display purposes.
GetEllipseStuff
This function extracts the ellipse data for the requested datum from
the arrays in the class file Geodesy.cls. It returns the ellipse's
major and minor axes as well as the ellipsoid name in an EllipseStruct.
GetDatumStuff
This function extracts the datum data for the requested datum from the
arrays in the class file Geodesy.cls. It returns the datum information in
a DatumStruct. The intent of the inclusion of the datum data is to allow
the user of an application to get to the ellipsoid information through
datum name which is commonly used in GPS receivers. The datumNumber is
geoid number for the ellipsoid associated with the named datum.
Suggested use: Read the datumNames into a list box in your application and allow the
user to select one and use its ListIndex+1 as the index for GetDatumStuff.
Then use the datumNumber as the geoid number to get to the underlying
ellipse data eMajor, eMinor and eName using GetEllipseStuff
LL2UTM
UTM2LL
These functions are implementations of the algorithms presented in the
USGS Professional Paper 1395 "Map Projections - a Working Manual" by John
P. Snyder.
LL2UTM converts a position defined by a latitude/longitude pair to it's
correspond UTM coordinates using a datum of the user's choice. The
function returns the requested information in a UTMStructure and returns
the error code WICNOERROR if no errors encountered in the conversion.
UTM2LL converts a position described by a UTM Easting/Northing and zone
to it's corresponding latitude/longitude. The requested information is
returned in a UTMStructure and the function returns WICNOERROR if
successful.
ModAzimuth
ModLatitude
ModLongitude
Modulus
These functions attempt to constrain their arguments to specific ranges.
ModAzimuth constrains an angle (in radians) to the range of 0 <= angle
<= 2*PI (0 to 360 deg). It is used for azimuths.
ModLatitude constrains an angle (in radians) to the range -PI/2 <= angle
>= +PI/2 (-90 deg to +90 deg). It is used for latitudes
ModLongitude constrains an angle (in radians) to the range -PI <= angle
>= PI (-180 deg to +180 deg). It is used for longitudes
Modulus is my implementation of the Mod function. It returns the remainde
of the division of x/y.
Reciprocal
This function returns the reciprocal of an azimuth. Azimuth is in decimal
degrees.
Square
This function returns the square of a value, i.e. Square(x) = x * x
Vdirect
Vinverse
These funcitions are the implementation of Vincenty's algorithms.
Given the latitude and longitude of a point and the azimuth and distance
to a second point, Vdirect returns the latitude and longitude of the
second point and the azimuth of the first point from the second. The
computed data is returned in a GeoStructure. The distance is returne
in meters and the azimuth is the angle measured from true north.The
function returns the standard WICNOERROR if successful.
Given the latitude and longitude of two points, Vinverse returns the
distance between the two points in meters and the azimuth of each point
from the other. These azimuths are NOT reciprocals. The functions returns
the standard WICNOERROR if successful.
Unzip the contents of Geodesy.Zip into a folder where you wish to run
the sample stuff. I have the VB project in a folder Geodesy on the VB
path. This will create a sample project for you to use to test the
code.
I have included some simple code to illustrate how these routines might
be used in a VB program. Cut and paste the Command1.Click and
Command2.click code (files Testxxx.txt) into the Geodesy project's
(Geodesy.vbp) GeoTest.frm module in place of the ones that is currently
there and run the program from the IDE.
If you have questions I will try to field them, but I can't guarantee
an instant response nor will I write complete projects for you. I would like
to hear about any additions you make to my code. Send the source
code please.
Remember this is an open source project and you are obligated
by the license to share the code and any improvements with anyone who would
like a copy. Please read the licensing agreement at the site documented
in the code.
To stay informed of future updates to the library, send me and an e-mail
with Geodesy in the subject line and I'll add you to the distribution
list.
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