UCVM API

Overview

The Unified California Velocity Model API (UCVM API) is a programming interface that allows the user to directly query multiple velocity models in a program. The API currently support these models:

• CVM-S
• CVM-H
• USGS Central California
• Hadley-Kanamori 1D

API

Data Types and Definitions

/* Maximum number of supported models */
#define UCVM_MAX_MODELS 10

/* Maximum projection description length */
#define UCVM_MAX_PROJ_LEN 256

/* Maximum model label length */
#define UCVM_MAX_LABEL_LEN 64

/* Maximum model version length */
#define UCVM_MAX_VERSION_LEN 64

/* Maximum path length */
#define UCVM_MAX_PATH_LEN 256

/* NO CVM flag */
#define UCVM_MODEL_NONE -1

/* Supported error codes */
typedef enum { UCVM_CODE_SUCCESS = 0, 
               UCVM_CODE_ERROR,
               UCVM_CODE_DATAGAP,
               UCVM_CODE_NODATA} ucvm_code_t;

/* Supported coordinate query modes */
typedef enum { UCVM_COORD_GEO_DEPTH = 0, 
               UCVM_COORD_UTM_DEPTH,
               UCVM_COORD_GEO_ELEV,
               UCVM_COORD_UTM_ELEV } ucvm_ctype_t;

/* Supported grid types */
typedef enum { UCVM_GRID_CELL_CENTER = 0, 
               UCVM_GRID_CELL_VERTEX} ucvm_gtype_t;

/* 3D point */
typedef struct ucvm_point_t 
{
  double coord[3];
} ucvm_point_t;

/* 3D dims */
typedef struct ucvm_dim_t 
{
  int dim[3];
} ucvm_dim_t;

/* Material properties */
typedef struct ucvm_prop_t 
{
  int model;
  double vp;
  double vs;
  double rho;
} ucvm_prop_t;

/* Region box */
typedef struct ucvm_region_t 
{
  ucvm_ctype_t cmode;
  double p1[3];
  double p2[3];
} ucvm_region_t;

/* Projection */
typedef struct ucvm_proj_t 
{
  char proj[UCVM_MAX_PROJ_LEN];
} ucvm_proj_t;

/* Projection transformation */
typedef struct ucvm_trans_t 
{
  double origin[3];
  double rotate;
  double translate[3];
  ucvm_gtype_t gtype;
} ucvm_trans_t;

/* Model */
typedef struct ucvm_model_t 
{
  char label[UCVM_MAX_LABEL_LEN];
  ucvm_region_t region;
  char config[UCVM_MAX_PATH_LEN];
  int (*init)(int id, ucvm_region_t *r, const char *config);
  int (*finalize)();
  const char* (*version)();
  int (*query)(ucvm_ctype_t cmode,
               int n, ucvm_point_t *pnt, 
               ucvm_prop_t *prop);
} ucvm_model_t;

UCVM Interface

Provides an interface for querying Vp, Vs, and rho from any supported model.

/* Initializer */
int ucvm_init(const char *config);

/* Finalizer */
int ucvm_finalize();

/* Set query mode */
int ucvm_query_mode(ucvm_ctype_t c);

/* Enable specific model, return new model id */
int ucvm_add_model(ucvm_model_t *m, int *id);

/* Get label for a model */
int ucvm_model_label(int m, char *label, int len);

/* Get version for a model */
int ucvm_model_version(int m, char *ver, int len);

/* Get model id from a label */
int ucvm_model_id(const char *label, int *id);

/* Query underlying models */
int ucvm_query(int n, ucvm_point_t *pnt, ucvm_prop_t *prop);

UCVM Grid Interface

Provides an interface for generating 2D regular grids in any USGS map projection.

/* Generate grid from projection and dimensions */
int ucvm_grid_gen(ucvm_proj_t *iproj, ucvm_trans_t *trans,
                  ucvm_proj_t *oproj,
                  ucvm_dim_t *dims, double spacing, 
                  ucvm_point_t *pnts);

/* Generate grid from projection and dimensions */
int ucvm_grid_gen_file(ucvm_proj_t *iproj, ucvm_trans_t *trans,
                       ucvm_proj_t *oproj,
                       ucvm_dim_t *dims, double spacing, 
                       const char *filename);

/* Convert point list from one projection to another */
int ucvm_grid_convert(ucvm_proj_t *iproj, 
                      ucvm_proj_t *oproj, 
                      size_t n, ucvm_point_t *pnts);

/* Convert point list from one projection to another */
int ucvm_grid_convert_file(ucvm_proj_t *iproj, 
                           ucvm_proj_t *oproj, 
                           size_t n, const char *filename);

Example Usage of API

The following code snippet illustrates how the API is used:

  int i;
  int nn = NUM_POINTS;
  ucvm_point_t *pnt1;
  ucvm_prop_t *prop1;
  
  int num_models;
  ucvm_model_t models[UCVM_MAX_MODELS];
  int model_ids[UCVM_MAX_MODELS];

  printf("Init\n");
  if (ucvm_init("./ucvm.conf") != UCVM_CODE_SUCCESS) {
    fprintf(stderr, "Init failed\n");
    return(1);
  }
  
  printf("Query Mode\n");
  if (ucvm_query_mode(UCVM_COORD_GEO_DEPTH) != UCVM_CODE_SUCCESS) {
    fprintf(stderr, "Set query mode failed\n");
    return(1);
  }
  
  printf("Get Model\n");
  if (ucvm_cvms_get_model(&(models[0])) != UCVM_CODE_SUCCESS) {
    fprintf(stderr, "Retrieval of CVM-S failed\n");
    return(1);
  }

  if (ucvm_add_model(&(models[0]), &(model_ids[0])) != UCVM_CODE_SUCCESS) {
    fprintf(stderr, "Enable CVM-S failed\n");
    return(1);
  }

  printf("Create points\n");
  for (i = 0; i < NUM_POINTS; i++) {
    pnt1[i].coord[0] = -119.0;
    pnt1[i].coord[1] = 31.0;
    pnt1[i].coord[2] = 2000.0;
  }

  printf("Query Models\n");
  if (ucvm_query(nn, pnt1, prop1) != UCVM_CODE_SUCCESS) {
    fprintf(stderr, "Query CVM failed\n");
    return(1);
  }
 
  printf("Results\n");
  for (i = 0; i < NUM_POINTS; i++) {
    printf("%d: model=%d, vp=%lf, vs=%lf, rho=%lf\n", i, 
           prop1[i].model, prop1[i].vp, prop1[i].vs, prop1[i].rho);
  }

 

Implementation Details

• Models are queried in the order they are enabled in the interface. The material properties for a particular (lon,lat) point are from the first model in the ordered list to return valid values.
• Only lon,lat,dep coordinates are currently supported
• No smoothing between models is performed. They are simply tiled.
• Projections are performed with the Proj.4 package

Future Improvements

• Addition of a high resolution state-wide DEM to allow query by elevation
• Addition of other regional models

 

Science Issues

Overlapping Models

Imagine the scenario outlined below, where the user wishes to combine two models, a SoCal model and a NoCal model:

The models may overlap in ways which makes merging them difficult.

• For a point that falls within the Kern County region, simply interpolating between the two models may not work if NoCal reports water properties (vp, rho, no vs) and the SoCal model reports soil/rock. No interpolation is possible in this case. To deal with this situation, there are several options:
  • Coordinate edits to each model to bring their material properties into better agreement within the overlap region.
  • Crop one or both models to remove the overlap, and smooth them into the California background model.
  • Create a new “Transition Model” that covers Kern County and surrounding area that interpolates/averages the the two other models in a scientifically acceptable way. Register this new model in the API, and give it priority over the other two models. In effect, tile the Transition Model, the NoCal Model, and the SoCal Model.
  • Allow the models to overlap with discontinuities. This is currently how the UCVM API handles overlap.

Projection Distortion

Several issues with map projections come into play:

• Distortion in projections on large scales. Any state-wide model that supports querying by UTM or other projection coordinates must account for and minimize distortion.
• Inconsistent handling of projections within models. Each model generally has its own internal projection. For example, CVM-H uses a UTM projection. The projection codes used across all models should be standardized on the Proj.4 projection package to avoid small differences in the handling of coordinates. This may require resampling of the data inside the models.

Standardized Handling of Elevation

All models that support query by elevation should use a standard DEM derived from the same source.