rt_band_get_pixel_line()

rt_errorstate rt_band_get_pixel_line	(	rt_band	band,
		int	x,
		int	y,
		uint16_t	len,
		void **	vals,
		uint16_t *	nvals
	)

Get values of multiple pixels.

Unlike rt_band_get_pixel, values in vals are of the band's pixel type so cannot be assumed to be double. Function uses memcpy.

It is important to be careful when using this function as the number of values being fetched may exceed a pixel "row". Remember that the band values are stored in a stream (1-D array) regardless of what the raster's width and height might be. So, getting a number of values may cross multiple pixel "rows".

Parameters

band	: the band to get pixel value from
x	: pixel column (0-based)
y	: pixel row (0-based)
len	: the number of pixels to get
**vals	: the pixel values
*nvals	: the number of pixel values being returned

Returns

ES_NONE on success, ES_ERROR on error

Definition at line 1288 of file rt_band.c.

  {
        uint8_t *_vals = NULL;
        int pixsize = 0;
        uint8_t *data = NULL;
        uint32_t offset = 0;
        uint16_t _nvals = 0;
        int maxlen = 0;
        uint8_t *ptr = NULL;
 
        assert(NULL != band);
        assert(vals != NULL && nvals != NULL);
 
        /* initialize to no values */
        *nvals = 0;
 
        if (
                x < 0 || x >= band->width ||
                y < 0 || y >= band->height
        ) {
                rtwarn("Attempting to get pixel values with out of range raster coordinates: (%d, %d)", x, y);
                return ES_ERROR;
        }
 
        if (len < 1)
                return ES_NONE;
 
        data = rt_band_get_data(band);
        if (data == NULL) {
                rterror("rt_band_get_pixel_line: Cannot get band data");
                return ES_ERROR;
        }
 
        /* +1 for the nodata value */
        offset = x + (y * band->width);
        RASTER_DEBUGF(4, "offset = %d", offset);
 
        pixsize = rt_pixtype_size(band->pixtype);
        RASTER_DEBUGF(4, "pixsize = %d", pixsize);
 
        /* cap _nvals so that it doesn't overflow */
        _nvals = len;
        maxlen = band->width * band->height;
 
        if (((int) (offset + _nvals)) > maxlen) {
                _nvals = maxlen - offset;
                rtwarn("Limiting returning number values to %d", _nvals);
        }
        RASTER_DEBUGF(4, "_nvals = %d", _nvals);
 
        ptr = data + ((size_t)offset * pixsize);
 
        _vals = rtalloc((size_t)_nvals * pixsize);
        if (_vals == NULL) {
                rterror("rt_band_get_pixel_line: Could not allocate memory for pixel values");
                return ES_ERROR;
        }
 
        /* copy pixels */
        memcpy(_vals, ptr, (size_t)_nvals * pixsize);
 
        *vals = _vals;
        *nvals = _nvals;
 
        return ES_NONE;
}

References ES_ERROR, ES_NONE, RASTER_DEBUGF, rt_band_get_data(), rt_pixtype_size(), rtalloc(), rterror(), and rtwarn().

Referenced by RASTER_tile(), RASTER_union_transfn(), and test_band_get_pixel_line().

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