LERCLoader

 

The LERCLoader parses the binary compressed raster format as described in LERC Byte Stream Specification.

LERC (Limited Error Raster Compression), also written Lerc, is a format for compressed raster image data. It was developed by Esri. It may appear in a file by itself, or as part of MRF format, or be used as a compression method in a format such as GeoTIFF. There are two major versions, known as "Lerc1" and "Lerc2".

Loader	Characteristic
File Extension	.lrc, .lerc, .lerc2, .lerc1
File Type	Binary
File Format	LERC
Data Format	Data structure
Decoder Type	Synchronous
Worker Thread Support	Yes
Streaming Support	No

Usage

import {LERCLoader} from '@loaders.gl/wms';
import {load} from '@loaders.gl/core';

// Form a LERC request
const url = `${WFS_SERVICE_URL}?REQUEST=GetFeature&...`;

const data = await load(url, LERCLoader, options);

Parsed Data Format

Data returned by LERCLoader

export type LERCData = {
  /**	Width of decoded image */
  width: number;
  /**	Height of decoded image */
  height: number;
  /**	The type of pixels represented in the output */
  pixelType: LercPixelType;
  /**	[statistics_band1, statistics_band2, …] Each element is a statistics object representing min and max values  */
  statistics: BandStats[];
  /**	[band1, band2, …] Each band is a typed array of width * height * depthCount */
  pixels: TypedArray[];
  /**	Typed array with a size of width*height, or null if all pixels are valid */
  mask: Uint8Array;
  /**	Depth count  */
  depthCount: number;
  /**	array	[band1_mask, band2_mask, …] Each band is a Uint8Array of width * height * depthCount */
  bandMasks?: Uint8Array[];
};

export type LercPixelType = 'S8' | 'U8' | 'S16' | 'U16' | 'S32' | 'U32' | 'F32' | 'F64';

export interface BandStats {
  minValue: number;
  maxValue: number;
  depthStats?: {
    minValues: Float64Array;
    maxValues: Float64Array;
  };
}

Options

Option	Type	Default	Description
lerc.inputOffset?	number	0	The number of bytes to skip in the input byte stream. A valid Lerc file is expected at that position
lerc.noDataValue?	number	false	It is recommended to use the returned mask instead of setting this value
lerc.returnInterleaved?	boolean	false	(ndepth LERC2 only) If true, returned depth values are pixel-interleaved