rt_raster_gdal_polygonize()

rt_geomval rt_raster_gdal_polygonize	(	rt_raster	raster,
		int	nband,
		int	exclude_nodata_value,
		int *	pnElements
	)

Returns a set of "geomval" value, one for each group of pixel sharing the same value for the provided band.

A "geomval" value is a complex type composed of a geometry in LWPOLY representation (one for each group of pixel sharing the same value) and the value associated with this geometry.

Parameters

raster	: the raster to get info from.
nband	: the band to polygonize. 0-based
exclude_nodata_value	: if non-zero, ignore nodata values to check for pixels with value

Returns

A set of "geomval" values, one for each group of pixels sharing the same value for the provided band. The returned values are LWPOLY geometries.

From GDALPolygonize function header: "Polygon features will be created on the output layer, with polygon geometries representing the polygons". So,the WKB geometry type should be "wkbPolygon"

Create a new field in the layer, to store the px value

Optimization: Apply a OGR SQL filter to the layer to select the features different from NODATA value.

Thanks to David Zwarg.

Definition at line 975 of file rt_geometry.c.

  {
        CPLErr cplerr = CE_None;
        char *pszQuery;
        long j;
        OGRSFDriverH ogr_drv = NULL;
        GDALDriverH gdal_drv = NULL;
        int destroy_gdal_drv = 0;
        GDALDatasetH memdataset = NULL;
        GDALRasterBandH gdal_band = NULL;
        OGRDataSourceH memdatasource = NULL;
        rt_geomval pols = NULL;
        OGRLayerH hLayer = NULL;
        OGRFeatureH hFeature = NULL;
        OGRGeometryH hGeom = NULL;
        OGRFieldDefnH hFldDfn = NULL;
        unsigned char *wkb = NULL;
        int wkbsize = 0;
        LWGEOM *lwgeom = NULL;
        int nFeatureCount = 0;
        rt_band band = NULL;
        int iPixVal = -1;
        double dValue = 0.0;
        int iBandHasNodataValue = FALSE;
        double dBandNoData = 0.0;
 
        uint32_t bandNums[1] = {nband};
        int excludeNodataValues[1] = {exclude_nodata_value};
 
        /* checks */
        assert(NULL != raster);
        assert(NULL != pnElements);
 
        RASTER_DEBUG(2, "In rt_raster_gdal_polygonize");
 
        *pnElements = 0;
 
        /*******************************
         * Get band
         *******************************/
        band = rt_raster_get_band(raster, nband);
        if (NULL == band) {
                rterror("rt_raster_gdal_polygonize: Error getting band %d from raster", nband);
                return NULL;
        }
 
        if (exclude_nodata_value) {
 
                /* band is NODATA */
                if (rt_band_get_isnodata_flag(band)) {
                        RASTER_DEBUG(3, "Band is NODATA.  Returning null");
                        *pnElements = 0;
                        return NULL;
                }
 
                iBandHasNodataValue = rt_band_get_hasnodata_flag(band);
                if (iBandHasNodataValue)
                        rt_band_get_nodata(band, &dBandNoData);
                else
                        exclude_nodata_value = FALSE;
        }
 
        /*****************************************************
         * Convert raster to GDAL MEM dataset
         *****************************************************/
        memdataset = rt_raster_to_gdal_mem(raster, NULL, bandNums, excludeNodataValues, 1, &gdal_drv, &destroy_gdal_drv);
        if (NULL == memdataset) {
                rterror("rt_raster_gdal_polygonize: Couldn't convert raster to GDAL MEM dataset");
                return NULL;
        }
 
        /*****************************
         * Register ogr mem driver
         *****************************/
#ifdef GDAL_DCAP_RASTER
        /* in GDAL 2.0, OGRRegisterAll() is an alias to GDALAllRegister() */
        rt_util_gdal_register_all(0);
#else
        OGRRegisterAll();
#endif
 
        RASTER_DEBUG(3, "creating OGR MEM vector");
 
        /*****************************************************
         * Create an OGR in-memory vector for layers
         *****************************************************/
        ogr_drv = OGRGetDriverByName("Memory");
        memdatasource = OGR_Dr_CreateDataSource(ogr_drv, "", NULL);
        if (NULL == memdatasource) {
                rterror("rt_raster_gdal_polygonize: Couldn't create a OGR Datasource to store pols");
                GDALClose(memdataset);
                if (destroy_gdal_drv) GDALDestroyDriver(gdal_drv);
                return NULL;
        }
 
        /* Can MEM driver create new layers? */
        if (!OGR_DS_TestCapability(memdatasource, ODsCCreateLayer)) {
                rterror("rt_raster_gdal_polygonize: MEM driver can't create new layers, aborting");
 
                /* xxx jorgearevalo: what should we do now? */
                GDALClose(memdataset);
                if (destroy_gdal_drv) GDALDestroyDriver(gdal_drv);
                OGRReleaseDataSource(memdatasource);
 
                return NULL;
        }
 
        RASTER_DEBUG(3, "polygonizying GDAL MEM raster band");
 
        /*****************************
         * Polygonize the raster band
         *****************************/
 
        hLayer = OGR_DS_CreateLayer(memdatasource, "PolygonizedLayer", NULL, wkbPolygon, NULL);
 
        if (NULL == hLayer) {
                rterror("rt_raster_gdal_polygonize: Couldn't create layer to store polygons");
 
                GDALClose(memdataset);
                if (destroy_gdal_drv) GDALDestroyDriver(gdal_drv);
                OGRReleaseDataSource(memdatasource);
 
                return NULL;
        }
 
        /* First, create a field definition to create the field */
        hFldDfn = OGR_Fld_Create("PixelValue", OFTReal);
 
        /* Second, create the field */
        if (OGR_L_CreateField(hLayer, hFldDfn, TRUE) != OGRERR_NONE) {
                rtwarn("Couldn't create a field in OGR Layer. The polygons generated won't be able to store the pixel value");
                iPixVal = -1;
        }
        else {
                /* Index to the new field created in the layer */
                iPixVal = 0;
        }
 
        /* Get GDAL raster band */
        gdal_band = GDALGetRasterBand(memdataset, 1);
        if (NULL == gdal_band) {
                rterror("rt_raster_gdal_polygonize: Couldn't get GDAL band to polygonize");
 
                GDALClose(memdataset);
                if (destroy_gdal_drv) GDALDestroyDriver(gdal_drv);
                OGR_Fld_Destroy(hFldDfn);
                OGR_DS_DeleteLayer(memdatasource, 0);
                OGRReleaseDataSource(memdatasource);
 
                return NULL;
        }
 
        /* We don't need a raster mask band. Each band has a nodata value. */
        cplerr = GDALFPolygonize(gdal_band, NULL, hLayer, iPixVal, NULL, NULL, NULL);
 
        if (cplerr != CE_None) {
                rterror("rt_raster_gdal_polygonize: Could not polygonize GDAL band");
 
                GDALClose(memdataset);
                if (destroy_gdal_drv) GDALDestroyDriver(gdal_drv);
                OGR_Fld_Destroy(hFldDfn);
                OGR_DS_DeleteLayer(memdatasource, 0);
                OGRReleaseDataSource(memdatasource);
 
                return NULL;
        }
 
        if (iBandHasNodataValue) {
                size_t sz = 50 * sizeof (char);
                pszQuery = (char *) rtalloc(sz);
                snprintf(pszQuery, sz, "PixelValue != %f", dBandNoData );
                OGRErr e = OGR_L_SetAttributeFilter(hLayer, pszQuery);
                if (e != OGRERR_NONE) {
                        rtwarn("Error filtering NODATA values for band. All values will be treated as data values");
                }
        }
        else {
                pszQuery = NULL;
        }
 
        /*********************************************************************
         * Transform OGR layers to WKB polygons
         * XXX jorgearevalo: GDALPolygonize does not set the coordinate system
         * on the output layer. Application code should do this when the layer
         * is created, presumably matching the raster coordinate system.
         *********************************************************************/
        nFeatureCount = OGR_L_GetFeatureCount(hLayer, TRUE);
 
        /* Allocate memory for pols */
        pols = (rt_geomval) rtalloc(nFeatureCount * sizeof(struct rt_geomval_t));
 
        if (NULL == pols) {
                rterror("rt_raster_gdal_polygonize: Could not allocate memory for geomval set");
 
                GDALClose(memdataset);
                if (destroy_gdal_drv) GDALDestroyDriver(gdal_drv);
                OGR_Fld_Destroy(hFldDfn);
                OGR_DS_DeleteLayer(memdatasource, 0);
                if (NULL != pszQuery)
                        rtdealloc(pszQuery);
                OGRReleaseDataSource(memdatasource);
 
                return NULL;
        }
 
        /* initialize GEOS */
        initGEOS(rtinfo, lwgeom_geos_error);
 
        RASTER_DEBUGF(3, "storing polygons (%d)", nFeatureCount);
 
        /* Reset feature reading to start in the first feature */
        OGR_L_ResetReading(hLayer);
 
        for (j = 0; j < nFeatureCount; j++) {
                hFeature = OGR_L_GetNextFeature(hLayer);
                dValue = OGR_F_GetFieldAsDouble(hFeature, iPixVal);
 
                hGeom = OGR_F_GetGeometryRef(hFeature);
                wkbsize = OGR_G_WkbSize(hGeom);
 
                /* allocate wkb buffer */
                wkb = rtalloc(sizeof(unsigned char) * wkbsize);
                if (wkb == NULL) {
                        rterror("rt_raster_gdal_polygonize: Could not allocate memory for WKB buffer");
 
                        OGR_F_Destroy(hFeature);
                        GDALClose(memdataset);
                        if (destroy_gdal_drv) GDALDestroyDriver(gdal_drv);
                        OGR_Fld_Destroy(hFldDfn);
                        OGR_DS_DeleteLayer(memdatasource, 0);
                        if (NULL != pszQuery)
                                rtdealloc(pszQuery);
                        OGRReleaseDataSource(memdatasource);
 
                        return NULL;
                }
 
                /* export WKB with LSB byte order */
                OGR_G_ExportToWkb(hGeom, wkbNDR, wkb);
 
                /* convert WKB to LWGEOM */
                lwgeom = lwgeom_from_wkb(wkb, wkbsize, LW_PARSER_CHECK_NONE);
 
#if POSTGIS_DEBUG_LEVEL > 3
                {
                        char *wkt = NULL;
                        OGR_G_ExportToWkt(hGeom, &wkt);
                        RASTER_DEBUGF(4, "GDAL wkt = %s", wkt);
                        CPLFree(wkt);
 
                        d_print_binary_hex("GDAL wkb", wkb, wkbsize);
                }
#endif
 
                /* cleanup unnecessary stuff */
                rtdealloc(wkb);
                wkb = NULL;
                wkbsize = 0;
 
                OGR_F_Destroy(hFeature);
 
                /* specify SRID */
                lwgeom_set_srid(lwgeom, rt_raster_get_srid(raster));
 
                /* save lwgeom */
                pols[j].geom = lwgeom_as_lwpoly(lwgeom);
 
#if POSTGIS_DEBUG_LEVEL > 3
                {
                        char *wkt = lwgeom_to_wkt(lwgeom, WKT_ISO, DBL_DIG, NULL);
                        RASTER_DEBUGF(4, "LWGEOM wkt = %s", wkt);
                        rtdealloc(wkt);
 
                        lwvarlena_t *lwwkb = lwgeom_to_wkb_varlena(lwgeom, WKB_ISO | WKB_NDR);
                        size_t lwwkbsize = LWSIZE_GET(lwwkb->size) - LWVARHDRSZ;
                        if (lwwkbsize) {
                                d_print_binary_hex("LWGEOM wkb", (const uint8_t *)lwwkb->data, lwwkbsize);
                                rtdealloc(lwwkb);
                        }
                }
#endif
 
                /* set pixel value */
                pols[j].val = dValue;
        }
 
        *pnElements = nFeatureCount;
 
        RASTER_DEBUG(3, "destroying GDAL MEM raster");
        GDALClose(memdataset);
        if (destroy_gdal_drv) GDALDestroyDriver(gdal_drv);
 
        RASTER_DEBUG(3, "destroying OGR MEM vector");
        OGR_Fld_Destroy(hFldDfn);
        OGR_DS_DeleteLayer(memdatasource, 0);
        if (NULL != pszQuery) rtdealloc(pszQuery);
        OGRReleaseDataSource(memdatasource);
 
        return pols;
}

References ovdump::band, lwvarlena_t::data, FALSE, rt_geomval_t::geom, LW_PARSER_CHECK_NONE, lwgeom_as_lwpoly(), lwgeom_from_wkb(), lwgeom_geos_error(), lwgeom_set_srid(), lwgeom_to_wkb_varlena(), lwgeom_to_wkt(), LWSIZE_GET, LWVARHDRSZ, pixval::nband, rtrowdump::raster, RASTER_DEBUG, RASTER_DEBUGF, rt_band_get_hasnodata_flag(), rt_band_get_isnodata_flag(), rt_band_get_nodata(), rt_raster_get_band(), rt_raster_get_srid(), rt_raster_to_gdal_mem(), rt_util_gdal_register_all(), rtalloc(), rtdealloc(), rterror(), rtinfo(), rtwarn(), lwvarlena_t::size, TRUE, rt_geomval_t::val, WKB_ISO, WKB_NDR, and WKT_ISO.

Referenced by RASTER_dumpAsPolygons(), rt_raster_surface(), and test_gdal_polygonize().

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