The GLG Map Server Application Programming Interface (API), provided as a set of C functions, provides a cross-platform way to incorporate the Map Server into an application. The API provides all functionality available in the Map Server executable as well as some advanced functionality to optimize the Map Server's performance. The API allows a developer to create multiple Map Objects and multiple Datasets, as well as cache vector and image data for enhanced performance.
The GLG Map Server is intended as a mapping service and therefore provides no way of displaying generated map images. However, the GLG GIS Object can be used to integrate the generated map images into a graphical GLG application.
If the GLG GIS Object is used, it will handle all invocations of the Map Server API transparently, so that the user does not need to know the Map Server API, and this chapter may be skipped.
The Map Server API provides functions to read data, create and manipulate Map Objects and write the generated images to a file, and is used in applications that do not use the GLG GIS Object.
In order to run an application utilizing the Map Server API on various platforms, the code simply needs to be recompiled. Although the Map Server API itself is completely cross-platform, it is up to the developer to make the rest of the application platform-independent.
The Map Server API utilizes the same resource mechanism that is used in the GLG Toolkit. Maps and Datasets are both objects whose resources can be Get and Set. Similarly, there are three types of resources: D, S and G which represent double, string and geometrical data. Both Maps and Datasets are GlmObjects. The basic resource access mechanism has the same format as in the GLG Toolkit. For example, to set the Height of a map object, a D resource:
GlmSetDResource( map_object, "Height", 600. ); // set the height GlmGetDResource( map_object, "Height", &height ); // getGeometrical resources are passed three values or pointers:
GlmSetGResource( map_object, "FillColor", 1., 0., 0. ); // set the color GlmGetGResource( map_object, "FillColor", &r, &g, &b ); // getString resources are passed a string or a pointer to a string:
GlmSetSResource( map_object, "Dataset", "earth.sdf" ); // set the string GlmSetSResource( map_object, "Dataset", &dataset ); // getThe basic structure of any mapping application requires:
Initialization of the Map Server
Specifying the desired attributes of the map image
Any mapping application must first include the file " GlmApi.h " via the #include directive. The initialization of the Map Server is accomplished via a call to the GlmInit() function. The function has one parameter, a string, which defines the path to a Server Dataset File (SDF). All layer and font information will be loaded from this file.
A Map Object is created via the GlmCreateMap() function. Its resources are set via the GlmSetResource functions. What follows is a detailed description of available resources. These are the same resources that are specified in the -oGISreq command line option.
Note : The type of the resource (D,G or S) is specified after the resource name.
Specifies the name of the dataset to use. The default is "DefaultDataset", which is always created by GlmInit function. If the application uses multiple datasets, the DatasetName resource is used to set the name of the dataset to be used for generating the map. If the DatasetName resource was changed, the GlmSetupMap function must be called before selecting layers.
Specifies which projection is to be used to render the map image. Valid values are GLM_ORTHOGRAPHIC and GLM_RECTANGULAR .
Defines the longitude at the center of the map image. A value of 0 is at the Greenwich meridian. Negative values are west of the meridian and positive values are east of the meridian.
Defines the latitude at the center of the map image. A value of 0 is at the equator. Negative values are below the equator and positive values are above the equator.
Defines the vertical extent of the map image. If using the rectangular projection, the extent is in latitudinal coordinates. If using the orthographic projection, the extent is in meters.
Defines the horizontal extent of the map image. If using the rectangular projection, the extent is in longitudinal coordinates. If using the orthographic projection, the extent is in meters.
For the rectangular projection, defines the map rotation angle, in degrees counter-clockwise.
Defines whether or not to maintain the correct lon/lat aspect ratio. If set to 1, the image will be stretched according to the Width and Height resources. If set to 0, the image will maintain its lon/lat aspect ratio. For example, in the orthographic projection, if the entire earth is being viewed, if Stretch is set to 0, the earth will always appear as a perfect sphere, instead of an oblong one.
Defines the background color to be rendered in the map image. The three values are in the range 0 to 1 and define the red, green and blue components of the color, respectively.
Enables or disables antialiasing while scaling images of raster layers. Will be turned on if set to 1 (default).
Defined whether or not to render errors into the image. If set to 1, errors will be rendered. If set to 0, they will not.
Defines the verbosity value. If verbosity level is set to positive integer value, from 1 to 6, diagnostic information will be generated. If verbosity level is set to a negative integer value, from -1 to -6, the performance and timing output will be produced. If verbosity level is set to the values 1001 or 1002, tile extent information is displayed in the generated images for the GetMap requests. The verbosity output is printed to the standard error, the higher the number, the more output is generated. Errors and info are also displayed in the generated image (if IERRORS is set to 1) and logged into the glm_error.log file. By default, the verbosity is set to 0.
Finally, the layers to be rendered into the map image need to be set. The most commonly used function is the GlmSetLayers function. It takes a comma separated list of layers as its parameter. It also takes " default " and "*" as valid layer names. If " default " is used as a layer name, all layers with the DEFAULT ON flag specified will be rendered, and if "*" is used as a layer name, all layers in the SDF file will be rendered. For example:
GlmSetLayers( map_object, "default,clouds,shores" );will turn on all default layers as well as the clouds and shores layer. Two other common functions are: GlmEnableLayer , which enables one layer, and GlmDisableLayer , which disables one layer in the map object. If the map object is used repeatedly, the GlmResetLayers function may be called to clear the previous selection prior to selecting new layers.
Once the Map Object is created and the resources set, the actual map generation needs to occur. This is accomplished with a call to GlmGetProjection() . Its one parameter is the map object with all its parameters specified. It is important to note that after the image is generated, the map object does not need to be discarded. It may be used to generate other images after altering some or all of the map object's resources.
After a call to GlmGetProjection , the GlmWriteImage function can be used to write the resulting map image into a file. For example:
GlmGetProjection( map_object ); GlmWriteImage( NULL, "output.jpg", map_object );generates a map image and writes it to a file called " output.jpg ". The first parameter may specify an open file handle. For example, to write them to the standard output, the following can be used:
GlmGetProjection( map_object ); GlmWriteImage( stdout, NULL, map_object );The GlmGetElevation, GlmGetLatLon, GlmGetXYZ and GlmConvert functions may be used to query elevation and perform coordinate conversion.
What follows is an example of a simple mapping application which creates a map object, generates a map image, and writes it to a file. It is available as a map_generation.c file the in the glg/map_server/src/ directory.
#include "GlgApi.h" #include "GlmApi.h" main() { GlmObject map; // The map object to be used // Loads a dataset from SDF file in the current directory or GLG_PATH GlmInit( "earth.sdf" ); // Creates the map object using default dataset created by GlgInit. map = GlmCreateMap(); // Sets the image width and height GlmSetDResource( map, "Width", 800. ); GlmSetDResource( map, "Height", 600. ); // Sets the map projection GlmSetDResource( map, "Projection", (double)GLM_ORTHOGRAPHIC ); // Sets the center lat/lon of the image GlmSetDResource( map, "CenterLat", 30. ); GlmSetDResource( map, "CenterLon", 0. ); // Sets the vertical and horizontal extents, in meters for the // ORTHOGRAPHIC projection. GlmSetDResource( map, "VExtent", 14000000. ); GlmSetDResource( map, "HExtent", 14000000. ); GlmSetDResource( map, "Stretch", 0. ); // Turns off X/Y stretching // Sets up the map object. It is optional here, but must be used // before selecting layers if the DatasetName resource was changed. GlmSetupMap( map ); // Clears any previous layer selections. GlmResetLayers( map ); // Enables the earth and clouds layers in the generated map. GlmSetLayers( map, "earth,clouds" ); GlmGetProjection( map ); // Generates the map image // Writes the image to a file GlmWriteImage( NULL, "output.jpg", map ); }The details of the process of linking an application program with the GLM Map Server library depends on the operating system and windowing environment where the application will run. Since the Map Server depends on the GLG Toolkit, GLG libraries will also need to be linked with.
The libglm_map.a library supplied with the GLG Map Server contains all functions in this guide. The Map Server uses the GLG Standard API and depends on the GLG library, libglg.a . The linking process also requires libz1 and libjpeg2 libraries, as well as libtiff3 and libfreetype4 libraries. All these libraries are provided in the lib subdirectory of the GLG Toolkit installation.
The following line shows a sample of the link statement for an application using the Map Server library on Solaris platform:
... -lglg -lglg_map -lz -ljpeg -ltiff -lfreetype -lXm -lXt -lX11 \If an application uses the Map Server but does not need the TrueType font support in the Map Server, the libfreetype library may be replaced with libfreetype_stub.
On Microsoft Windows, the Map Server library is included into the GLG library. To use Map Server, simply link with either the GLG Standard or Extended API library.
You can choose whether to use a static or dynamic library. The static version of the GLG Standard API library is called GlgLib.lib , and the static version of the Extended API is called GlgExLib.lib . In order to use the static version of either GLG Standard or Extended API library, define GLG_STATIC in your code:
#define GLG_STATICThis must appear before the GlmApi.h and GlgApi.h include files.
The static version of the GLG libraries was compiled using the multi-threaded DLL compilation option. Your code must be compiled using the same option in order to link your application with the GLG static libraries.
The DLL version of the GLG Standard API library is called Glm.dll , and the DLL version of the Extended API is called GlgEx.dll . To use them, you must link your program with Glg.lib or GlgEx.lib .
The GLG Extended API DLL is called GlgEx.dll and includes the GLG Standard API DLL. This means you don't have to link with the Glg.dll if using GlgEx.dll . Link only with the GlgEx.lib library to use the Extended Library DLL.
In order to use the Map Server library, both GlgApi.h and GlmApi.h need to be included. They reside in the glg/include directory. See page 88 for an example.
Occasionally, simply creating and manipulating a map object is not sufficient. For example, a developer might want to change the color of roads rendered into a map image. In order to accomplish this, resources of layers and datasets need to be set. In the Map Server, datasets and layers are also GlmObjects. By manipulating these objects and setting their resources many custom effects can be accomplished.
All datasets are held in an array called GlmDatasetArray. Each dataset holds layer objects. Map Objects are entirely separate. Map Objects require that a dataset be associated with them. This is accomplished by setting the "Dataset" resource, an S resource, of the map object. By default, this is not necessary, but if multiple datasets are to be created, each Map Object needs to know which dataset it will be using.
For example, if there are three datasets, and three different map objects:
GlmSetSResource( map1, "Dataset", "Earth1" ); GlmSetSResource( map2, "Dataset", "Earth2" ); GlmSetSResource( map3, "Dataset", "Earth3" );If only one dataset is being used, using NULL as the object in GlmGetResource and GlmSetResource calls will set resources of layers. Layers are accessed by name, so for example:
GlmSetDResource( NULL, "clouds/Alpha", 0.5 );will change the transparency of the clouds layer in the default dataset. If multiple datasets are used, the dataset object returned by GlmCreateDataSet can be used. For example:
data_obj = GlmCreateDataset( "mydata", "mydata.sdf" ); GlmSetDResource( data_obj, "clouds/Alpha", 0.5 );See Creating Datasets on page 92 for details.
If the GLG Extended API is used, the dataset and layer objects can be modified directly. For example, the following code will retrieve a dataset named " mydata ", retrieve from it a layer called clouds, and set its transparency.
GlmObject layer; layer = GlgGetResourceObject( GlmDatasetArray, "mydata/clouds" ); GlmSetDResource( layer, "Alpha", 0.5 );If more than one dataset is desired, the GlmCreateDataset function can be used. The function returns a GlmObject which has already been added to the dataset array. Its parameters are the name of the dataset and the SDF to load it from. For example, the following code creates a dataset called " mydata " and sets it as the dataset to use for a given map object:
GlmObject map; GlmCreateDataset( "mydata", "mydata.sdf" ); map = GlmCreateMap(); GlmSetSResource( map, "Dataset", "mydata" );The dataset resources are almost identical to the attributes available in SDF files, but instead may be accessed through a programmatic interface. Dataset resources must be set prior to generation of a map image in which they will be used. Refer to the Datasets on page 28 for more information about each resource.
The resource type is listed after each resource name and may be D (double), S (string) or G (RGB color triplet or XYZ coordinate).
Layers, just like datasets and maps, are also GlmObjects. What follows is a description of all resources that can be set in a layer. The resources available are almost identical to the attributes available in LIF files, but instead may be accessed through a programmatic interface. Layer resources must be set prior to generation of a map image in which they will be used. Refer to the Configuration Variables on page 33 for more information about each resource.
The resource type is listed after each resource name and may be D (double), S (string) or G (RGB color triplet or XYZ coordinate).
Specifies the layer type: GLM_IMAGE, GLM_VECTOR, GLM_GRID or GLM_OUTLINE . This resource is set when the layer is created and must not be changed afterwards.
Defines whether or not a layer will be turned on by default. Will be turned on if set to 1.
Defines what blending function is to be used when rendering the layer. This variable is very similar to the use of blending functions in OpenGL. It has four supported values:
GLM_OPAQUE GLM_ALPHA_WHITE_OPAQUE GLM_ALPHA_BLACK GLM_TRANSPARENT_COLOR_OPAQUE GLM_XOR GLM_BUMP_MAPSee Structure of Data and File Layout on page 25 for details.
Defines the transparent color value for the GLM_TRANSPARENT_COLOR_OPAQUE rendering mode.
Defines the transparent color matching precision in the range from 0 to 1 for the GLM_TRANSPARENT_COLOR_OPAQUE rendering mode.
Specifies the elevation mode for the layer:
GLM_ELEVATION_NONE GLM_ELEVATION_DATA GLM_ELEVATION_COLORThe GLM_ELEVATION_COLOR mode is used to display elevation data as a color-coded image. The GLM_ELEVATION_DATA mode is used for elevation queries.
Defines the transparency of the layer, ranging from 0 to 1. An alpha value of 0 will make the layer invisible, while an alpha value of 1 will make the layer fully opaque according to the blending function.
For raster layers, enables or disables antialiasing when scaling images. Will be turned on if set to 1 (default).
Defines the maximum number of tiles a layer can require before the fallback is activated.
Specifies the minimal pixel size for map decluttering. All polygons whose pixel extent at the current zoom level is smaller than this parameter will not be drawn. The default value of the parameter is 1.
Defines the maximum time (in seconds) the Map Server waits for the lock file before proceeding. The default value is 0.3 seconds.
Defines the width of the image data in pixels if the layer is one which uses raster image data.
Defines the height of the image data in pixels if the layer is one which uses raster image data.
Defines the interval between neighboring horizontal (of equal latitude) lines. This variable is only useful if the type of the layer is set to GRID.
Defines an adaptive number grid. The Map Server will attempt to divide the extent of the map image into roughly the number of grid lines specified by the variable's value, while placing the grid lines on round numbers.
Defines whether or not to render labels next to grid lines. A value of 0 will not render grid labels, value of 1 (default) will render labels on one side of the map, and the value of 2 will render them on both sides.
Defines the format for displaying the fractional part of the grid labels: decimals are used if set to 1 (default), minutes and seconds are used if set to 0.
Defines how the font will be rendered and how font units will be defined. This variable has three supported values:
GLM_FLAT GLM_MAPPED_FLAT GLM_TRANSFORMEDSee TEXT TYPE=<type> on page 41 for details.
A bitwise OR of the horizontal and vertical anchoring types for rendering text labels.
GLM_HLEFT GLM_HRIGHT GLM_HCENTER GLM_VTOP GLM_VBOTTOM GLM_VCENTERSpecifies optional rendering attributes for text labels. Must be a bitwise OR of all desired options. Supported options are:
GLM_TEXT_BG_EDGE GLM_TEXT_BG_FILL GLM_TEXT_OUTLINEDefines the top, bottom, left and right margin in pixels between the text and its text box.
Defines the line width in pixels of the text box drawn around text labels. Text box drawing is enabled by setting LABEL STYLE to include BG_EDGE and/or BG_FILL .
Defines the range of zoom factor for which marker labels (such as city names) and polygon labels (such as street names) are displayed.
Defines the type of the label layout negotiation and may have values of GLM_LAYOUT_NONE, GLM_LAYOUT_LAYER and GLM_LAYOUT_GLOBAL .
Defines label priority for all labels in the layer. The labels with priority value of 0 have the highest priority. A threshold table may be attached to label priority to vary priority of labels within one layer based on other object attributes, such as a road type or city population. While the priority values may be set to any number greater or equal to 0, using priority values with minimal gaps between them results in better performance.
Defines an additional margin in pixels between text labels. Using a bigger value will result in more space between individual text labels when the label layout negotiation is enabled.
Defines what type of marker to render at the location defined by the text object's control point. Must be a bitwise OR of all desired types. Possible types:
GLM_CROSS GLM_BOX GLM_FILLED_BOX GLM_CIRCLE GLM_FILLED_CIRCLE GLM_DOT GLM_CUSTOM_ICONDefines the distance in pixels that the text and/or text box should be rendered from the marker.
Defines the fill type of polygons for vector layers. Valid values are:
GLM_EDGE GLM_FILL GLM_FILL_AND_EDGEDefines the line width in pixels of polygons, grid lines and outline, analogous to the line width option in the GLG Toolkit. The default value is 1 pixel.
Defines the type of polygon label to render. Valid values are:
GLM_LINE_LABEL GLM_MID_LINE_LABEL GLM_AREA_LABEL GLM_BBOX_LABELDefines layer's data as volatile if set to 1 (default value is 0). Volatile data are checked before they are used and re-read if the data have changed since the last time they were used. This resource is set when the layer is created and must not be changed afterwards.
Specifies the name of the redirect file for volatile layers. This resource is set when the layer is created and must not be changed afterwards.
Specifies the redirect prefix for volatile layers. This resource is read from the redirect file and must not be changed.
Specifies the name of a fallback layer to switch to when the maximum number of tiles is exceeded. This resource is set when the layer is created and must not be changed afterwards.
Suppresses errors for missing tiles, which may not be an error in case of square tiling of vector datasets. When tiling such datasets, the tiles that do not contain any data are not written out. It may also be used with image layers that use square tiling, but some of the tiles are not provided.
Loads an SDF file and creates a dataset.
GlmObject GlmCreateDataset( dataset_name, filename ) char * dataset_name; char * filename;The SDF file that contains the dataset's information. If filename is NULL, an empty dataset with no layers is created.
This function creates a new dataset object and adds to it layers defined in the SDF file. The function returns the dataset object it created. The dataset may later be accessed using either its name or object ID.
Loads a LIF file and creates a layer.
GlmObject GlmAddLayer( dataset_name, layer_name, filename ) char * dataset_name; char * layer_name; char * filename;The LIF file that contains the layer's information, must not be NULL.
This function reads a LIF file and creates a new layer object for it, adding the layer object to the specified dataset. The function returns the layer object that was created. The layer may later be accessed using either its name or object ID.
Returns a newly created map object.
GlmObject GlmCreateMap( void )This function creates a new map object which may be used to generate map images. It also holds attributes of map requests.
Sets up the map object after changing its DatasetName resource.
GlmBoolean GlmSetupMap( map ) GlmObject map;Enables the specified layers in the map object
void GlmSetLayers( map, layers ) GlmObject map; char * layers;A comma separated string of layers to enable.
This function enables all the layers and aliases specified in the layers string. All other layers are disabled. If "default" is used as a layer name, all layers that are ON by default will be enabled. If "*" is used as a layer name, all layers will be enabled. If a layer name starts with `-', the layer is disabled. This may be used to disable some layers enabled by the "default" or "*" layer string values. If individual layers are listed, their names should match those in the SDF file. The layers will be displayed in the order of their appearance in the layer string. For layers enabled by the "default" or "*" values of the layer string, their display order is defined by the order in which the layers are listed in the SDF file. The "++" prefix may be used to override zoom and number of tiles limits defined in the layer file. The attribute conditions may be appended to layer names. Refer to the description of the LAYERS string on page 56 for more information.
Resets any previously selected layers in the map object.
void GlmResetLayers( map ) GlmObject map;Specifies the name of the layer to enable.
This function enables one layer. the layer name can be " default " or "*". If the layer does not exist, an error is generated. If " default " is used a layer name, all layers which have the DEFAULT ON flag defined will be turned on. if "*" is used as a layer name, all layers in the SDF file will be turned on.
Specifies the name of the layer to disable.
This function disables one layer. the layer name can be "default" or "*". If the layer does not exist, an error is generated. If "default" is used a layer name, all layers which have the DEFAULT ON flag defined will be turned off. if "*" is used as a layer name, all layers in the SDF file will be turned off.
Returns the current value of a scalar resource.
GlgBoolean GlmGetDResource( object, resource_name, d_value_ptr ) GlmObject object; char * resource_name; double * d_value_ptr;Returns the set of three values making up a geometrical resource:
GlgBoolean GlmGetGResource( object, resource_name, g_value1, g_value2, g_value3 ) GlmObject object; char * resource_name; double * g_value1_ptr, * g_value2_ptr, * gvalue3_ptr;Specify pointers to the locations to which the XYZ or RGB values of the resource are returned.
If a geometrical resource with the input name exists, this function copies its current three values to the addresses specified with the g_value pointers and returns GlgTrue . Otherwise it generates an error message and returns GlgFalse .
For a geometrical point, g_value0_ptr , g_value1_ptr and g_value2_ptr are set to the X, Y and Z coordinates of the point, respectively. For a color resource, they will be set to the R, G and B values of the color, respectively.
Returns the value of a string resource.
GlgBoolean GlmGetSResource( object, resource_name, s_value_ptr ) GlmObject object; char * resource_name; char ** s_value_ptr;A pointer for returning the resource value.
If a string resource with the given name exists, this function sets the s_value_ptr to point to the internal string value and returns GlgTrue . Otherwise it returns GlgFalse .
Warning : The returned pointer points to GLG internal data structures and should not be modified. The pointer is valid only immediately after a call to the GlmGetSResource function. To store the returned string, create a copy of it using the GlgStrClone function.
Sets a new value for a resource of type D.
GlgBoolean GlmSetDResource( object, resource_name, d_value ) GlmObject object; char * resource_name; double d_value;Sets the values of a geometrical resource.
GlgBoolean GlmSetGResource( object, resource_name, g_value1, g_value2, g_value3 ) GlgObject object; char * resource_name; double g_value1, g_value2, g_value3;Replaces the string in a string resource.
GlgBoolean GlmSetSResource( object, resource_name, s_value ) GlmObject object; char * resource_name; char * s_value;Specifies the new string for the resource.
If a string resource with the given name exists, this function creates a copy of the input string, and sets that copy as the new value of the resource. The function returns GlgTrue if the resource has been successfully changed, otherwise it generates an error message and returns GlgFalse . The memory associated with the old string is automatically freed.
Generates a map image and stores it in the map object.
void GlmGetProjection( map ) GlmObject map;Writes the image in the map object to a file.
GlgBoolean GlmWriteImage( file, filename, map ) FILE * file; char * filename; GlmObject map;Returns elevation of the specified lat/lon point.
GlgBoolean GlmGetElevation( map, layer_name, lat, lon, elevation ) GlmObject map; char * layer_name; double lat, lon double * elevation ;Specifies the map object used to generate a map image. The map object has to be in an updated state. If the map object has been just created or changed since the last call to the GlmGetProjection or GlmUpdateMap functions, it has to be updated using the GlmUpdateMap function prior to invoking GlmGetLatLon .
Specifies the name of the elevation layer to query. The layer must have ELEVATION MODE=DATA setting in the LIF file.
Converts X/Y coordinates of a point on the map to lat/lon coordinates.
GlgBoolean GlmGetLatLon( map, x, y, lat_lon ) GlmObject map; double x, y; GlgPo int * lat_lon;Specifies the map object used to generate a map image. The map object has to be in an updated state. If the map object has been just created or changed since the last call to the GlmGetProjection or GlmUpdateMap functions, it has to be updated using the GlmUpdateMap function prior to invoking GlmGetLatLon .
Specifies a pointer to GlgPoint structure for returning lat/lon coordinates.
This function converts the X/Y image coordinates to the lat/lon coordinates using information in the map object. The image coordinate system has its origin in the upper left corner. The longitude is returned as the x field of the GlgPoint structure, and the latitude is returned as the y field. The function returns GlgFalse if the X/Y point is outside of the map image area, or outside of the globe area if the orthographic projection is used.
Converts lat/lon coordinates of a point to the X/Y screen coordinates of the map image.
void GlmGetLatLon( map, lat, lon, xyz ) GlmObject map; double lat, lon; GlgPo int * xyz;Specifies the map object used to generate a map image. The map object has to be in an updated state. If the map object has been just created or changed since the last call to the GlmGetProjection or GlmUpdateMap functions, it has to be updated using the GlmUpdateMap function prior to invoking GlmGetLatLon .
Specifies a pointer to GlgPoint structure for returning X/Y coordinates.
This function converts the lat/lon coordinates to X/Y image coordinates using information in the map object. The image coordinate system has origin in the upper left corner. The z coordinate of the returned structure is set to a negative value if the point is outside of the visible area of the map when the rectangular projection is used. When the orthographic projection is used, the z coordinate is set to a negative value if the point is on the invisible part of the globe, and to zero when the point is on the edge of the globe. In the orthographic projection, the returned X and Y values may be outside of the image area and must be checked before they are used.
A low level function that performs coordinate conversion between the GIS coordinates of a map and the X/Y coordinates of the drawing without the use of a map object.
void GlmConvert( projection, stretch, coord_type, coord_to_lat_lon, center, extent, angle,The type of the coordinate system to convert to or from: GLG_SCREEN_COORD for screen coordinates or GLG_OBJECT_COORD for the GLG world coordinates.
GlgTrue to convert from X/Y coordinates to GIS longitude and latitude, GlgFalse to convert from lat/lon to X/Y coordinates.
A pointer to the GlgPoint structure containing lat/lon coordinates of the map center. The Z coordinate must be set to 0.
A pointer to the GlgPoint structure containing X and Y extent of the map in the selected projection: in degrees for the rectangular projection or in meters for the orthographic projection. The Z extent must be set to 0.
A map image extent in the selected coordinate system. To get X/Y coordinates relative to the map image origin, use min_x=0, min_y=0, max_x=image_width, max_y=image_height .
A pointer to the GlgPoint structure that receives converted coordinate values.
When converting from X/Y to lat/lon coordinates in the orthographic projection, the Z coordinate is set to a negative value for points on the invisible part of the globe or outside the globe area, and to zero for points on the edge of the globe. The coordinates of the returned point may be outside of the visible portion of the map for all projections.
Updates the map object in preparation for invoking GlmGetElevation , GlmGetLatLon and GlmGetXYZ functions.
GlgBoolean GlmUpdateMap( map ) GlmObject map;Specifies the map object to update after it has been created or its parameters have been changed since the last call to the GlmGetProjection or GlmUpdateMap functions.
This function sets up internals of the map objects to prepare for a more efficient handling of multiple calls to elevation query and coordinate conversion functions. By encapsulating setup into a separate function, it may be performed just once per a series of queries, instead of doing it for each query. The function returns GlgFalse in case of errors in data setup.
Resets any accumulated error messages that are about to be displayed in the generated map image:
void GlmResetImageErrors( void )Removes a layer from the dataset.
void GlmRemoveLayer( dataset_name, layer_name ) char * dataset_name; char * layer_name;