rt_warp.c

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/*
 *
 * WKTRaster - Raster Types for PostGIS
 * http://trac.osgeo.org/postgis/wiki/WKTRaster
 *
 * Copyright (C) 2013 Bborie Park <dustymugs@gmail.com>
 * Copyright (C) 2011-2013 Regents of the University of California
 *   <bkpark@ucdavis.edu>
 * Copyright (C) 2010-2011 Jorge Arevalo <jorge.arevalo@deimos-space.com>
 * Copyright (C) 2010-2011 David Zwarg <dzwarg@azavea.com>
 * Copyright (C) 2009-2011 Pierre Racine <pierre.racine@sbf.ulaval.ca>
 * Copyright (C) 2009-2011 Mateusz Loskot <mateusz@loskot.net>
 * Copyright (C) 2008-2009 Sandro Santilli <strk@kbt.io>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 */
 
#include "../../postgis_config.h"
 
#include "librtcore.h"
#include "librtcore_internal.h"
 
/******************************************************************************
* rt_raster_gdal_warp()
******************************************************************************/
 
typedef struct _rti_warp_arg_t* _rti_warp_arg;
struct _rti_warp_arg_t {
 
        struct {
                GDALDriverH drv;
                GDALDatasetH ds;
                char *srs;
                int destroy_drv;
        } src, dst;
 
        GDALWarpOptions *wopts;
 
        struct {
                struct {
                        char **item;
                        int len;
                } option;
 
                struct {
                        void *transform;
                        void *imgproj;
                        void *approx;
                } arg;
 
                GDALTransformerFunc func;
        } transform;
 
};
 
static _rti_warp_arg
_rti_warp_arg_init() {
        _rti_warp_arg arg = NULL;
 
        arg = rtalloc(sizeof(struct _rti_warp_arg_t));
        if (arg == NULL) {
                rterror("_rti_warp_arg_init: Could not allocate memory for _rti_warp_arg");
                return NULL;
        }
 
        arg->src.drv = NULL;
        arg->src.destroy_drv = 0;
        arg->src.ds = NULL;
        arg->src.srs = NULL;
 
        arg->dst.drv = NULL;
        arg->dst.destroy_drv = 0;
        arg->dst.ds = NULL;
        arg->dst.srs = NULL;
 
        arg->wopts = NULL;
 
        arg->transform.option.item = NULL;
        arg->transform.option.len = 0;
 
        arg->transform.arg.transform = NULL;
        arg->transform.arg.imgproj = NULL;
        arg->transform.arg.approx = NULL;
 
        arg->transform.func = NULL;
 
        return arg;
}
 
static void
_rti_warp_arg_destroy(_rti_warp_arg arg) {
        int i = 0;
 
        if (arg->dst.ds != NULL)
                GDALClose(arg->dst.ds);
        if (arg->dst.srs != NULL)
                CPLFree(arg->dst.srs);
 
        if (arg->dst.drv != NULL && arg->dst.destroy_drv) {
                GDALDeregisterDriver(arg->dst.drv);
                GDALDestroyDriver(arg->dst.drv);
        }
 
        if (arg->src.ds != NULL)
                GDALClose(arg->src.ds);
        if (arg->src.srs != NULL)
                CPLFree(arg->src.srs);
 
        if (arg->src.drv != NULL && arg->src.destroy_drv) {
                GDALDeregisterDriver(arg->src.drv);
                GDALDestroyDriver(arg->src.drv);
        }
 
        if (arg->transform.func == GDALApproxTransform) {
                if (arg->transform.arg.imgproj != NULL)
                        GDALDestroyGenImgProjTransformer(arg->transform.arg.imgproj);
        }
 
        if (arg->wopts != NULL)
                GDALDestroyWarpOptions(arg->wopts);
 
        if (arg->transform.option.len > 0 && arg->transform.option.item != NULL) {
                for (i = 0; i < arg->transform.option.len; i++) {
                        if (arg->transform.option.item[i] != NULL)
                                rtdealloc(arg->transform.option.item[i]);
                }
                rtdealloc(arg->transform.option.item);
        }
 
        rtdealloc(arg);
        arg = NULL;
}
 
rt_raster rt_raster_gdal_warp(
        rt_raster raster,
        const char *src_srs, const char *dst_srs,
        double *scale_x, double *scale_y,
        int *width, int *height,
        double *ul_xw, double *ul_yw,
        double *grid_xw, double *grid_yw,
        double *skew_x, double *skew_y,
        GDALResampleAlg resample_alg, double max_err
) {
        CPLErr cplerr;
        char *dst_options[] = {"SUBCLASS=VRTWarpedDataset", NULL};
        _rti_warp_arg arg = NULL;
 
        GDALRasterBandH band;
        rt_band rtband = NULL;
        rt_pixtype pt = PT_END;
        GDALDataType gdal_pt = GDT_Unknown;
        double nodata = 0.0;
 
        double _gt[6] = {0};
        double dst_extent[4];
        rt_envelope extent;
 
        int _dim[2] = {0};
        double _skew[2] = {0};
        double _scale[2] = {0};
        int ul_user = 0;
 
        rt_raster rast = NULL;
        int i = 0;
        int numBands = 0;
 
        /* flag indicating that the spatial info is being substituted */
        int subspatial = 0;
 
        RASTER_DEBUG(3, "starting");
 
        assert(NULL != raster);
 
        /* internal variables */
        arg = _rti_warp_arg_init();
        if (arg == NULL) {
                rterror("rt_raster_gdal_warp: Could not initialize internal variables");
                return NULL;
        }
 
        /*
                max_err must be gte zero
 
                the value 0.125 is the default used in gdalwarp.cpp on line 283
        */
        if (max_err < 0.) max_err = 0.125;
        RASTER_DEBUGF(4, "max_err = %f", max_err);
 
        /* handle srs */
        if (src_srs != NULL) {
                /* reprojection taking place */
                if (dst_srs != NULL && strcmp(src_srs, dst_srs) != 0) {
                        RASTER_DEBUG(4, "Warp operation does include a reprojection");
                        arg->src.srs = rt_util_gdal_convert_sr(src_srs, 0);
                        arg->dst.srs = rt_util_gdal_convert_sr(dst_srs, 0);
 
                        if (arg->src.srs == NULL || arg->dst.srs == NULL) {
                                rterror("rt_raster_gdal_warp: Could not convert srs values to GDAL accepted format");
                                _rti_warp_arg_destroy(arg);
                                return NULL;
                        }
                }
                /* no reprojection, a stub just for clarity */
                else {
                        RASTER_DEBUG(4, "Warp operation does NOT include reprojection");
                }
        }
        else if (dst_srs != NULL) {
                /* dst_srs provided but not src_srs */
                rterror("rt_raster_gdal_warp: SRS required for input raster if SRS provided for warped raster");
                _rti_warp_arg_destroy(arg);
                return NULL;
        }
 
        /* load raster into a GDAL MEM dataset */
        arg->src.ds = rt_raster_to_gdal_mem(raster, arg->src.srs, NULL, NULL, 0, &(arg->src.drv), &(arg->src.destroy_drv));
        if (NULL == arg->src.ds) {
                rterror("rt_raster_gdal_warp: Could not convert raster to GDAL MEM format");
                _rti_warp_arg_destroy(arg);
                return NULL;
        }
        RASTER_DEBUG(3, "raster loaded into GDAL MEM dataset");
 
        /* special case when src_srs and dst_srs is NULL and raster's geotransform matrix is default */
        if (
                src_srs == NULL && dst_srs == NULL &&
                rt_raster_get_srid(raster) == SRID_UNKNOWN
        ) {
                double gt[6];
 
#if POSTGIS_DEBUG_LEVEL > 3
                GDALGetGeoTransform(arg->src.ds, gt);
                RASTER_DEBUGF(3, "GDAL MEM geotransform: %f, %f, %f, %f, %f, %f",
                        gt[0], gt[1], gt[2], gt[3], gt[4], gt[5]);
#endif
 
                /* default geotransform */
                rt_raster_get_geotransform_matrix(raster, gt);
                RASTER_DEBUGF(3, "raster geotransform: %f, %f, %f, %f, %f, %f",
                        gt[0], gt[1], gt[2], gt[3], gt[4], gt[5]);
 
                /* substitute spatial info (lack of) with a real one EPSG:32731 (WGS84/UTM zone 31s) */
                if (FLT_EQ(gt[0], 0.0) && FLT_EQ(gt[3], 0.0) && FLT_EQ(gt[1], 1.0) && FLT_EQ(gt[5], -1.0) &&
                    FLT_EQ(gt[2], 0.0) && FLT_EQ(gt[4], 0.0))
                {
                        double ngt[6] = {166021.4431, 0.1, 0, 10000000.0000, 0, -0.1};
 
                        rtwarn("Raster has default geotransform. Adjusting metadata for use of GDAL Warp API");
 
                        subspatial = 1;
 
                        GDALSetGeoTransform(arg->src.ds, ngt);
                        GDALFlushCache(arg->src.ds);
 
                        /* EPSG:32731 */
                        arg->src.srs = rt_util_gdal_convert_sr("EPSG:32731", 0);
                        arg->dst.srs = rt_util_gdal_convert_sr("EPSG:32731", 0);
 
#if POSTGIS_DEBUG_LEVEL > 3
                        GDALGetGeoTransform(arg->src.ds, gt);
                        RASTER_DEBUGF(3, "GDAL MEM geotransform: %f, %f, %f, %f, %f, %f",
                                gt[0], gt[1], gt[2], gt[3], gt[4], gt[5]);
#endif
                }
        }
 
        /* set transform options */
        if (arg->src.srs != NULL || arg->dst.srs != NULL) {
                arg->transform.option.len = 2;
                arg->transform.option.item = rtalloc(sizeof(char *) * (arg->transform.option.len + 1));
                if (NULL == arg->transform.option.item) {
                        rterror("rt_raster_gdal_warp: Could not allocation memory for transform options");
                        _rti_warp_arg_destroy(arg);
                        return NULL;
                }
                memset(arg->transform.option.item, 0, sizeof(char *) * (arg->transform.option.len + 1));
 
                for (i = 0; i < arg->transform.option.len; i++) {
                        const char *srs = i ? arg->dst.srs : arg->src.srs;
                        const char *lbl = i ? "DST_SRS=" : "SRC_SRS=";
                        size_t sz = sizeof(char) * (strlen(lbl) + 1);
                        if ( srs ) sz += strlen(srs);
                        arg->transform.option.item[i] = (char *) rtalloc(sz);
                        if (NULL == arg->transform.option.item[i]) {
                                rterror("rt_raster_gdal_warp: Could not allocation memory for transform options");
                                _rti_warp_arg_destroy(arg);
                                return NULL;
                        }
                        sprintf(arg->transform.option.item[i], "%s%s", lbl, srs ? srs : "");
                        RASTER_DEBUGF(4, "arg->transform.option.item[%d] = %s", i, arg->transform.option.item[i]);
                }
        }
        else
                arg->transform.option.len = 0;
 
        /* transformation object for building dst dataset */
        arg->transform.arg.transform = GDALCreateGenImgProjTransformer2(arg->src.ds, NULL, arg->transform.option.item);
        if (NULL == arg->transform.arg.transform) {
                rterror("rt_raster_gdal_warp: Could not create GDAL transformation object for output dataset creation");
                _rti_warp_arg_destroy(arg);
                return NULL;
        }
 
        /* get approximate output georeferenced bounds and resolution */
        cplerr = GDALSuggestedWarpOutput2(
                arg->src.ds, GDALGenImgProjTransform,
                arg->transform.arg.transform, _gt, &(_dim[0]), &(_dim[1]), dst_extent, 0);
        if (cplerr != CE_None) {
                rterror("rt_raster_gdal_warp: Could not get GDAL suggested warp output for output dataset creation");
                _rti_warp_arg_destroy(arg);
                return NULL;
        }
        GDALDestroyGenImgProjTransformer(arg->transform.arg.transform);
        arg->transform.arg.transform = NULL;
 
        /*
                don't use suggested dimensions as use of suggested scales
                on suggested extent will result in suggested dimensions
        */
        _dim[0] = 0;
        _dim[1] = 0;
 
        RASTER_DEBUGF(3, "Suggested geotransform: %f, %f, %f, %f, %f, %f",
                _gt[0], _gt[1], _gt[2], _gt[3], _gt[4], _gt[5]);
 
        /* store extent in easier-to-use object */
        extent.MinX = dst_extent[0];
        extent.MinY = dst_extent[1];
        extent.MaxX = dst_extent[2];
        extent.MaxY = dst_extent[3];
 
        extent.UpperLeftX = dst_extent[0];
        extent.UpperLeftY = dst_extent[3];
 
        RASTER_DEBUGF(3, "Suggested extent: %f, %f, %f, %f",
                extent.MinX, extent.MinY, extent.MaxX, extent.MaxY);
 
        /* scale and width/height are mutually exclusive */
        if (
                ((NULL != scale_x) || (NULL != scale_y)) &&
                ((NULL != width) || (NULL != height))
        ) {
                rterror("rt_raster_gdal_warp: Scale X/Y and width/height are mutually exclusive.  Only provide one");
                _rti_warp_arg_destroy(arg);
                return NULL;
        }
 
        /* user-defined width */
        if (NULL != width) {
                _dim[0] = abs(*width);
                _scale[0] = fabs((extent.MaxX - extent.MinX) / ((double) _dim[0]));
        }
        /* user-defined height */
        if (NULL != height) {
                _dim[1] = abs(*height);
                _scale[1] = fabs((extent.MaxY - extent.MinY) / ((double) _dim[1]));
        }
 
        /* user-defined scale */
        if (
                ((NULL != scale_x) && (FLT_NEQ(*scale_x, 0.0))) &&
                ((NULL != scale_y) && (FLT_NEQ(*scale_y, 0.0)))
        ) {
                _scale[0] = fabs(*scale_x);
                _scale[1] = fabs(*scale_y);
 
                /* special override since we changed the original GT scales */
                if (subspatial) {
                        /*
                        _scale[0] *= 10;
                        _scale[1] *= 10;
                        */
                        _scale[0] /= 10;
                        _scale[1] /= 10;
                }
        }
        else if (
                ((NULL != scale_x) && (NULL == scale_y)) ||
                ((NULL == scale_x) && (NULL != scale_y))
        ) {
                rterror("rt_raster_gdal_warp: Both X and Y scale values must be provided for scale");
                _rti_warp_arg_destroy(arg);
                return NULL;
        }
 
        /* scale not defined, use suggested */
        if (FLT_EQ(_scale[0], 0.0) && FLT_EQ(_scale[1], 0.0))
        {
                _scale[0] = fabs(_gt[1]);
                _scale[1] = fabs(_gt[5]);
        }
 
        RASTER_DEBUGF(4, "Using scale: %f x %f", _scale[0], -1 * _scale[1]);
 
        /* user-defined skew */
        if (NULL != skew_x) {
                _skew[0] = *skew_x;
 
                /*
                        negative scale-x affects skew
                        for now, force skew to be in left-right, top-down orientation
                */
                if (
                        NULL != scale_x &&
                        *scale_x < 0.
                ) {
                        _skew[0] *= -1;
                }
        }
        if (NULL != skew_y) {
                _skew[1] = *skew_y;
 
                /*
                        positive scale-y affects skew
                        for now, force skew to be in left-right, top-down orientation
                */
                if (
                        NULL != scale_y &&
                        *scale_y > 0.
                ) {
                        _skew[1] *= -1;
                }
        }
 
        RASTER_DEBUGF(4, "Using skew: %f x %f", _skew[0], _skew[1]);
 
        /* reprocess extent if skewed */
        if (FLT_NEQ(_skew[0], 0.0) || FLT_NEQ(_skew[1], 0.0))
        {
                rt_raster skewedrast;
 
                RASTER_DEBUG(3, "Computing skewed extent's envelope");
 
                skewedrast = rt_raster_compute_skewed_raster(
                        extent,
                        _skew,
                        _scale,
                        0.01
                );
                if (skewedrast == NULL) {
                        rterror("rt_raster_gdal_warp: Could not compute skewed raster");
                        _rti_warp_arg_destroy(arg);
                        return NULL;
                }
 
                if (_dim[0] == 0)
                        _dim[0] = skewedrast->width;
                if (_dim[1] == 0)
                        _dim[1] = skewedrast->height;
 
                extent.UpperLeftX = skewedrast->ipX;
                extent.UpperLeftY = skewedrast->ipY;
 
                rt_raster_destroy(skewedrast);
        }
 
        /* dimensions not defined, compute */
        if (!_dim[0])
                _dim[0] = (int) fmax((fabs(extent.MaxX - extent.MinX) + (_scale[0] / 2.)) / _scale[0], 1);
        if (!_dim[1])
                _dim[1] = (int) fmax((fabs(extent.MaxY - extent.MinY) + (_scale[1] / 2.)) / _scale[1], 1);
 
        /* temporary raster */
        rast = rt_raster_new(_dim[0], _dim[1]);
        if (rast == NULL) {
                rterror("rt_raster_gdal_warp: Out of memory allocating temporary raster");
                _rti_warp_arg_destroy(arg);
                return NULL;
        }
 
        /* set raster's spatial attributes */
        rt_raster_set_offsets(rast, extent.UpperLeftX, extent.UpperLeftY);
        rt_raster_set_scale(rast, _scale[0], -1 * _scale[1]);
        rt_raster_set_skews(rast, _skew[0], _skew[1]);
 
        rt_raster_get_geotransform_matrix(rast, _gt);
        RASTER_DEBUGF(3, "Temp raster's geotransform: %f, %f, %f, %f, %f, %f",
                _gt[0], _gt[1], _gt[2], _gt[3], _gt[4], _gt[5]);
        RASTER_DEBUGF(3, "Temp raster's dimensions (width x height): %d x %d",
                _dim[0], _dim[1]);
 
        /* user-defined upper-left corner */
        if (
                NULL != ul_xw &&
                NULL != ul_yw
        ) {
                ul_user = 1;
 
                RASTER_DEBUGF(4, "Using user-specified upper-left corner: %f, %f", *ul_xw, *ul_yw);
 
                /* set upper-left corner */
                rt_raster_set_offsets(rast, *ul_xw, *ul_yw);
                extent.UpperLeftX = *ul_xw;
                extent.UpperLeftY = *ul_yw;
        }
        else if (
                ((NULL != ul_xw) && (NULL == ul_yw)) ||
                ((NULL == ul_xw) && (NULL != ul_yw))
        ) {
                rterror("rt_raster_gdal_warp: Both X and Y upper-left corner values must be provided");
                rt_raster_destroy(rast);
                _rti_warp_arg_destroy(arg);
                return NULL;
        }
 
        /* alignment only considered if upper-left corner not provided */
        if (
                !ul_user && (
                        (NULL != grid_xw) || (NULL != grid_yw)
                )
        ) {
 
                if (
                        ((NULL != grid_xw) && (NULL == grid_yw)) ||
                        ((NULL == grid_xw) && (NULL != grid_yw))
                ) {
                        rterror("rt_raster_gdal_warp: Both X and Y alignment values must be provided");
                        rt_raster_destroy(rast);
                        _rti_warp_arg_destroy(arg);
                        return NULL;
                }
 
                RASTER_DEBUGF(4, "Aligning extent to user-specified grid: %f, %f", *grid_xw, *grid_yw);
 
                do {
                        double _r[2] = {0};
                        double _w[2] = {0};
 
                        /* raster is already aligned */
                        if (FLT_EQ(*grid_xw, extent.UpperLeftX) && FLT_EQ(*grid_yw, extent.UpperLeftY)) {
                                RASTER_DEBUG(3, "Skipping raster alignment as it is already aligned to grid");
                                break;
                        }
 
                        extent.UpperLeftX = rast->ipX;
                        extent.UpperLeftY = rast->ipY;
                        rt_raster_set_offsets(rast, *grid_xw, *grid_yw);
 
                        /* process upper-left corner */
                        if (rt_raster_geopoint_to_cell(
                                rast,
                                extent.UpperLeftX, extent.UpperLeftY,
                                &(_r[0]), &(_r[1]),
                                NULL
                        ) != ES_NONE) {
                                rterror("rt_raster_gdal_warp: Could not compute raster pixel for spatial coordinates");
                                rt_raster_destroy(rast);
                                _rti_warp_arg_destroy(arg);
                                return NULL;
                        }
 
                        if (rt_raster_cell_to_geopoint(
                                rast,
                                _r[0], _r[1],
                                &(_w[0]), &(_w[1]),
                                NULL
                        ) != ES_NONE) {
                                rterror("rt_raster_gdal_warp: Could not compute spatial coordinates for raster pixel");
 
                                rt_raster_destroy(rast);
                                _rti_warp_arg_destroy(arg);
                                return NULL;
                        }
 
                        /* shift occurred */
                        if (FLT_NEQ(_w[0], extent.UpperLeftX)) {
                                if (NULL == width)
                                        rast->width++;
                                else if (NULL == scale_x) {
                                        double _c[2] = {0};
 
                                        rt_raster_set_offsets(rast, extent.UpperLeftX, extent.UpperLeftY);
 
                                        /* get upper-right corner */
                                        if (rt_raster_cell_to_geopoint(
                                                rast,
                                                rast->width, 0,
                                                &(_c[0]), &(_c[1]),
                                                NULL
                                        ) != ES_NONE) {
                                                rterror("rt_raster_gdal_warp: Could not compute spatial coordinates for raster pixel");
                                                rt_raster_destroy(rast);
                                                _rti_warp_arg_destroy(arg);
                                                return NULL;
                                        }
 
                                        rast->scaleX = fabs((_c[0] - _w[0]) / ((double) rast->width));
                                }
                        }
                        if (FLT_NEQ(_w[1], extent.UpperLeftY)) {
                                if (NULL == height)
                                        rast->height++;
                                else if (NULL == scale_y) {
                                        double _c[2] = {0};
 
                                        rt_raster_set_offsets(rast, extent.UpperLeftX, extent.UpperLeftY);
 
                                        /* get upper-right corner */
                                        if (rt_raster_cell_to_geopoint(
                                                rast,
                                                0, rast->height,
                                                &(_c[0]), &(_c[1]),
                                                NULL
                                        ) != ES_NONE) {
                                                rterror("rt_raster_gdal_warp: Could not compute spatial coordinates for raster pixel");
 
                                                rt_raster_destroy(rast);
                                                _rti_warp_arg_destroy(arg);
                                                return NULL;
                                        }
 
                                        rast->scaleY = -1 * fabs((_c[1] - _w[1]) / ((double) rast->height));
                                }
                        }
 
                        rt_raster_set_offsets(rast, _w[0], _w[1]);
                        RASTER_DEBUGF(4, "aligned offsets: %f x %f", _w[0], _w[1]);
                }
                while (0);
        }
 
        /*
                after this point, rt_envelope extent is no longer used
        */
 
        /* get key attributes from rast */
        _dim[0] = rast->width;
        _dim[1] = rast->height;
        rt_raster_get_geotransform_matrix(rast, _gt);
 
        /* scale-x is negative or scale-y is positive */
        if ((
                (NULL != scale_x) && (*scale_x < 0.)
        ) || (
                (NULL != scale_y) && (*scale_y > 0)
        )) {
                double _w[2] = {0};
 
                /* negative scale-x */
                if (
                        (NULL != scale_x) &&
                        (*scale_x < 0.)
                ) {
                        if (rt_raster_cell_to_geopoint(
                                rast,
                                rast->width, 0,
                                &(_w[0]), &(_w[1]),
                                NULL
                        ) != ES_NONE) {
                                rterror("rt_raster_gdal_warp: Could not compute spatial coordinates for raster pixel");
                                rt_raster_destroy(rast);
                                _rti_warp_arg_destroy(arg);
                                return NULL;
                        }
 
                        _gt[0] = _w[0];
                        _gt[1] = *scale_x;
 
                        /* check for skew */
                        if (NULL != skew_x && FLT_NEQ(*skew_x, 0.0))
                                _gt[2] = *skew_x;
                }
                /* positive scale-y */
                if (
                        (NULL != scale_y) &&
                        (*scale_y > 0)
                ) {
                        if (rt_raster_cell_to_geopoint(
                                rast,
                                0, rast->height,
                                &(_w[0]), &(_w[1]),
                                NULL
                        ) != ES_NONE) {
                                rterror("rt_raster_gdal_warp: Could not compute spatial coordinates for raster pixel");
                                rt_raster_destroy(rast);
                                _rti_warp_arg_destroy(arg);
                                return NULL;
                        }
 
                        _gt[3] = _w[1];
                        _gt[5] = *scale_y;
 
                        /* check for skew */
                        if (NULL != skew_y && FLT_NEQ(*skew_y, 0.0))
                                _gt[4] = *skew_y;
                }
        }
 
        rt_raster_destroy(rast);
        rast = NULL;
 
        RASTER_DEBUGF(3, "Applied geotransform: %f, %f, %f, %f, %f, %f",
                _gt[0], _gt[1], _gt[2], _gt[3], _gt[4], _gt[5]);
        RASTER_DEBUGF(3, "Raster dimensions (width x height): %d x %d",
                _dim[0], _dim[1]);
 
        if ( _dim[0] == 0 || _dim[1] == 0 ) {
                rterror("rt_raster_gdal_warp: The width (%d) or height (%d) of the warped raster is zero", _dim[0], _dim[1]);
                _rti_warp_arg_destroy(arg);
                return NULL;
        }
 
        /* load VRT driver */
        if (!rt_util_gdal_driver_registered("VRT")) {
                RASTER_DEBUG(3, "Registering VRT driver");
                GDALRegister_VRT();
                arg->dst.destroy_drv = 1;
        }
        arg->dst.drv = GDALGetDriverByName("VRT");
        if (NULL == arg->dst.drv) {
                rterror("rt_raster_gdal_warp: Could not load the output GDAL VRT driver");
                _rti_warp_arg_destroy(arg);
                return NULL;
        }
 
        /* create dst dataset */
        arg->dst.ds = GDALCreate(arg->dst.drv, "", _dim[0], _dim[1], 0, GDT_Byte, dst_options);
        if (NULL == arg->dst.ds) {
                rterror("rt_raster_gdal_warp: Could not create GDAL VRT dataset");
                _rti_warp_arg_destroy(arg);
                return NULL;
        }
 
        /* set dst srs */
        if (arg->dst.srs != NULL) {
                cplerr = GDALSetProjection(arg->dst.ds, arg->dst.srs);
                if (cplerr != CE_None) {
                        rterror("rt_raster_gdal_warp: Could not set projection");
                        _rti_warp_arg_destroy(arg);
                        return NULL;
                }
                RASTER_DEBUGF(3, "Applied SRS: %s", GDALGetProjectionRef(arg->dst.ds));
        }
 
        /* set dst geotransform */
        cplerr = GDALSetGeoTransform(arg->dst.ds, _gt);
        if (cplerr != CE_None) {
                rterror("rt_raster_gdal_warp: Could not set geotransform");
                _rti_warp_arg_destroy(arg);
                return NULL;
        }
 
        /* add bands to dst dataset */
        numBands = rt_raster_get_num_bands(raster);
        for (i = 0; i < numBands; i++) {
                rtband = rt_raster_get_band(raster, i);
                if (NULL == rtband) {
                        rterror("rt_raster_gdal_warp: Could not get band %d for adding to VRT dataset", i);
                        _rti_warp_arg_destroy(arg);
                        return NULL;
                }
 
                pt = rt_band_get_pixtype(rtband);
                gdal_pt = rt_util_pixtype_to_gdal_datatype(pt);
                if (gdal_pt == GDT_Unknown)
                        rtwarn("rt_raster_gdal_warp: Unknown pixel type for band %d", i);
 
                cplerr = GDALAddBand(arg->dst.ds, gdal_pt, NULL);
                if (cplerr != CE_None) {
                        rterror("rt_raster_gdal_warp: Could not add band to VRT dataset");
                        _rti_warp_arg_destroy(arg);
                        return NULL;
                }
 
                /* get band to write data to */
                band = NULL;
                band = GDALGetRasterBand(arg->dst.ds, i + 1);
                if (NULL == band) {
                        rterror("rt_raster_gdal_warp: Could not get GDAL band for additional processing");
                        _rti_warp_arg_destroy(arg);
                        return NULL;
                }
 
                /* set nodata */
                if (rt_band_get_hasnodata_flag(rtband) != FALSE) {
                        rt_band_get_nodata(rtband, &nodata);
                        if (GDALSetRasterNoDataValue(band, nodata) != CE_None)
                                rtwarn("rt_raster_gdal_warp: Could not set nodata value for band %d", i);
                        RASTER_DEBUGF(3, "nodata value set to %f", GDALGetRasterNoDataValue(band, NULL));
                }
        }
 
        /* create transformation object */
        arg->transform.arg.transform = arg->transform.arg.imgproj = GDALCreateGenImgProjTransformer2(
                arg->src.ds, arg->dst.ds,
                arg->transform.option.item
        );
        if (NULL == arg->transform.arg.transform) {
                rterror("rt_raster_gdal_warp: Could not create GDAL transformation object");
                _rti_warp_arg_destroy(arg);
                return NULL;
        }
        arg->transform.func = GDALGenImgProjTransform;
 
        /* use approximate transformation object */
        if (max_err > 0.0) {
                arg->transform.arg.transform = arg->transform.arg.approx = GDALCreateApproxTransformer(
                        GDALGenImgProjTransform,
                        arg->transform.arg.imgproj, max_err
                );
                if (NULL == arg->transform.arg.transform) {
                        rterror("rt_raster_gdal_warp: Could not create GDAL approximate transformation object");
                        _rti_warp_arg_destroy(arg);
                        return NULL;
                }
 
                arg->transform.func = GDALApproxTransform;
        }
 
        /* warp options */
        arg->wopts = GDALCreateWarpOptions();
        if (NULL == arg->wopts) {
                rterror("rt_raster_gdal_warp: Could not create GDAL warp options object");
                _rti_warp_arg_destroy(arg);
                return NULL;
        }
 
        /* set options */
        arg->wopts->eResampleAlg = resample_alg;
        arg->wopts->hSrcDS = arg->src.ds;
        arg->wopts->hDstDS = arg->dst.ds;
        arg->wopts->pfnTransformer = arg->transform.func;
        arg->wopts->pTransformerArg = arg->transform.arg.transform;
        arg->wopts->papszWarpOptions = (char **) CPLMalloc(sizeof(char *) * 2);
 
        arg->wopts->papszWarpOptions[0] = (char *) CPLMalloc(sizeof(char) * (strlen("INIT_DEST=NO_DATA") + 1));
        strcpy(arg->wopts->papszWarpOptions[0], "INIT_DEST=NO_DATA");
        arg->wopts->papszWarpOptions[1] = NULL;
 
        /* set band mapping */
        arg->wopts->nBandCount = numBands;
        arg->wopts->panSrcBands = (int *) CPLMalloc(sizeof(int) * arg->wopts->nBandCount);
        arg->wopts->panDstBands = (int *) CPLMalloc(sizeof(int) * arg->wopts->nBandCount);
        for (i = 0; i < arg->wopts->nBandCount; i++)
                arg->wopts->panDstBands[i] = arg->wopts->panSrcBands[i] = i + 1;
 
        /*
        * https://trac.osgeo.org/postgis/ticket/5881
        * In order to call GDALWarp with BAND_INIT=NO_DATA we need to ensure
        * that the src and dst rasters have nodata values and they are
        * matched up nicely. This block used by tested with the hasnodata
        * check on all src raster bands, but now we just do it every time
        * because that makes sense (any warped raster is likely to have
        * empty corners on output, and those corners need to be filled with
        * some kind of NODATA value).
        */
        {
                RASTER_DEBUG(3, "Setting nodata mapping");
                arg->wopts->padfSrcNoDataReal = (double *) CPLMalloc(numBands * sizeof(double));
                arg->wopts->padfDstNoDataReal = (double *) CPLMalloc(numBands * sizeof(double));
                arg->wopts->padfSrcNoDataImag = (double *) CPLMalloc(numBands * sizeof(double));
                arg->wopts->padfDstNoDataImag = (double *) CPLMalloc(numBands * sizeof(double));
                if (
                        NULL == arg->wopts->padfSrcNoDataReal ||
                        NULL == arg->wopts->padfDstNoDataReal ||
                        NULL == arg->wopts->padfSrcNoDataImag ||
                        NULL == arg->wopts->padfDstNoDataImag
                ) {
                        rterror("rt_raster_gdal_warp: Out of memory allocating nodata mapping");
                        _rti_warp_arg_destroy(arg);
                        return NULL;
                }
                for (i = 0; i < numBands; i++) {
                        band = rt_raster_get_band(raster, i);
                        if (!band) {
                                rterror("rt_raster_gdal_warp: Could not process bands for nodata values");
                                _rti_warp_arg_destroy(arg);
                                return NULL;
                        }
 
                        if (!rt_band_get_hasnodata_flag(band)) {
                                /*
                                        based on line 1004 of gdalwarp.cpp
                                        the problem is that there is a chance that this number is a legitimate value
                                */
                                arg->wopts->padfSrcNoDataReal[i] = -123456.789;
                        }
                        else {
                                rt_band_get_nodata(band, &(arg->wopts->padfSrcNoDataReal[i]));
                        }
 
                        arg->wopts->padfDstNoDataReal[i] = arg->wopts->padfSrcNoDataReal[i];
                        arg->wopts->padfDstNoDataImag[i] = arg->wopts->padfSrcNoDataImag[i] = 0.0;
                        RASTER_DEBUGF(4, "Mapped nodata value for band %d: %f (%f) => %f (%f)",
                                i,
                                arg->wopts->padfSrcNoDataReal[i], arg->wopts->padfSrcNoDataImag[i],
                                arg->wopts->padfDstNoDataReal[i], arg->wopts->padfDstNoDataImag[i]
                        );
                }
        }
 
        /* warp raster */
        RASTER_DEBUG(3, "Warping raster");
        cplerr = GDALInitializeWarpedVRT(arg->dst.ds, arg->wopts);
        if (cplerr != CE_None) {
                rterror("rt_raster_gdal_warp: Could not warp raster");
                _rti_warp_arg_destroy(arg);
                return NULL;
        }
        /*
        GDALSetDescription(arg->dst.ds, "/tmp/warped.vrt");
        */
        GDALFlushCache(arg->dst.ds);
        RASTER_DEBUG(3, "Raster warped");
 
        /* convert gdal dataset to raster */
        RASTER_DEBUG(3, "Converting GDAL dataset to raster");
        rast = rt_raster_from_gdal_dataset(arg->dst.ds);
 
        _rti_warp_arg_destroy(arg);
 
        if (NULL == rast) {
                rterror("rt_raster_gdal_warp: Could not warp raster");
                return NULL;
        }
 
        /* substitute spatial, reset back to default */
        if (subspatial) {
                double gt[6] = {0, 1, 0, 0, 0, -1};
                /* See http://trac.osgeo.org/postgis/ticket/2911 */
                /* We should probably also tweak rotation here */
                /* NOTE: the times 10 is because it was divided by 10 in a section above,
                 *       I'm not sure the above division was needed */
                gt[1] = _scale[0] * 10;
                gt[5] = -1 * _scale[1] * 10;
 
                rt_raster_set_geotransform_matrix(rast, gt);
                rt_raster_set_srid(rast, SRID_UNKNOWN);
        }
 
        RASTER_DEBUG(3, "done");
 
        return rast;
}