Latitude/Longitude Class
This article was contributed by
George Chastain.
In my line of work, my colleagues and I often need to add
controls to a user interface to allow the user to enter
geographic latitudes and longitudes.
The need to provide an interface that allows for the consistently correct
entry of coordinates is usually great.
I finally decided to sit down and create classes to provide good
usuable controls for entering latitudes and longitudes. These class
are CGCLatitudeCtrl and CGCLongitudeCtrl.
The demo program supplied with this article illustrates the capabilities of
these classes.
The classes are derived from a class, CGCColorEdit, I created for edit boxes
that provides different color and font capabilities. The CGCColorEdit class
is similar to other classes found elsewhere on this site so I will not dwell on its
design.
The CGCLatitudeCtrl and CGCLongitudeCtrl classes are very simple to use. Each
control divides its display into four different fields; 1) a hemisphere field,
2) a degrees field, 3) a minutes field and 4) a seconds field.
The user can navigate between fields within the control using the left and right
arrow keys. Navigation to the right may also be achieved using the space bar.
When the use navigates to a particular field within the control, that field is
selected and highlighted. Actions taken by the user will affect that field.
The up and down arrow keys may be used to increment or decrement, respectively,
the currently selected field. In addition, the user may enter values for that field
directly using the number keys on the keyboard.
The user may also select a specific field within the control by clicking on it with
the left mouse button. The user can zero out the currently-selected field by
pressing the backspace key.
A context menu is even provided. When the user clicks over the control that has
focus using the right mouse button, a context menu is displayed. It allows the user
to zero the entire control setting or to zero out only the currently-selected field.
There are even "hot keys" defined for the control.
When the control has focus, the user may jump to the hemisphere field by pressing
the "h" key. Similarly, the user may jump to the degrees, minutes or seconds field
by pressing the "d", "m" or "x" keys, respectively.
There are three methods defined for each class in addition to those inherited from
CGCColorEdit. These are:
The method Set() allows the application to initialize the control to any setting
valid for that type of control (latitude or longitude).
BOOL Set(const HEMISPHERE_TYPE hsph,
const UINT Degrees,
const UINT Minutes,
const float Seconds);
The method Get() allows the application to obtain the current setting, usually
from within an EN_CHANGE handler.
Article text goes here
void Get(HEMISPHERE_TYPE& hsph,
UINT& Degrees,
UINT& Minutes,
float& Seconds) const;
The method GetDecimalDegrees() allows the application to obtain the current setting
in decimal degrees.
double GetDecimalDegrees()const;
Here are the steps to place a latitude control and a longitude control on your user
interface:
1. Add CGCColorEdit class to your project.
2. Add CGCLatitudeCtrl class to your project.
3. Add CGCLongitudeCtrl class to your project.
4. Place an edit box using the Resource Editor to be used for your latitude
control.
5. Place an edit box using the Resource Editor to be used for your
longitude control.
4. Using ClassWizard, create a member variable of type
CGCLatitudeCtrl for one of the new edit boxes.
5. Use ClassWizard to create a member variable of type
CGCLongitudeCtrl for the other new edit box.
6. Add an EN_CHANGE handler for each of the new edit boxes
to your parent window to handle when the controls change as you
would any other control class.
I hope that these will prove useful to someone on future projects.
Downloads
Download demo application - 158 Kb
Download demo source - 94 Kb
History
Date Posted: December 18, 1999
Date Updated: December 28, 1999
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