itowns/lib/Parser/ISGParser.js

A JS/WebGL framework for 3D geospatial data visualization

import * as THREE from 'three';
import { Extent } from '@itowns/geographic';
import GeoidGrid from "../Core/Geographic/GeoidGrid.js";
import { getHeaderAttribute } from "./GDFParser.js";
import { BYTES_PER_DOUBLE } from "./GTXParser.js";

/**
 * The `ISGParser` module provides a `[parse]{@link module:ISGParser.parse}` method. This method takes the content of a
 * ISG file in, and returns a `{@link GeoidGrid}`. the `{@link GeoidGrid}` contains all the necessary attributes and
 * methods to access the ISG data in iTowns.
 *
 * @module ISGParser
 */
export default {
  /**
   * Parses an ISG file content and returns a corresponding {@link GeoidGrid}.
   *
   * @param   {string}    isg                             The content of the ISG file to parse.
   * @param   {Object}    options                         An object gathering the optional parameters to pass to
                                                          * the parser.
   * @param   {Object}    [options.in={}]                 Information on the ISG data.
   * @param   {string}    [options.in.crs='EPSG:4326']    The Coordinates Reference System (CRS) of the ISG data.
                                                          * It must be a geographic CRS, and must be given as an EPSG
                                                          * code.
   *
   * @returns {Promise<GeoidGrid>}    A promise resolving with a {@link GeoidGrid}, which contains all the necessary
                                      * attributes and methods to access ISG file data.
   */
  parse(isg) {
    let options = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : {
      in: {}
    };
    const rows = isg.split('\n');
    const firstMeasureLine = rows.indexOf(rows.find(row => row.includes('end_of_head'))) + 1;
    const rawHeaderData = rows.slice(0, firstMeasureLine);

    // ---------- GET METADATA FROM THE FILE : ----------

    const metadata = {
      minX: getHeaderAttribute(rawHeaderData, 'lon min'),
      maxX: getHeaderAttribute(rawHeaderData, 'lon max'),
      minY: getHeaderAttribute(rawHeaderData, 'lat min'),
      maxY: getHeaderAttribute(rawHeaderData, 'lat max'),
      stepX: getHeaderAttribute(rawHeaderData, 'delta lon'),
      stepY: getHeaderAttribute(rawHeaderData, 'delta lat'),
      nRows: getHeaderAttribute(rawHeaderData, 'nrows'),
      nColumns: getHeaderAttribute(rawHeaderData, 'ncols')
    };

    // ---------- BUILD A DATA VIEWER FROM THE TEXT DATA : ----------

    const data = new DataView(new ArrayBuffer(BYTES_PER_DOUBLE * metadata.nRows * metadata.nColumns));
    let index = 0;
    for (let row of rows.slice(firstMeasureLine, rows.length)) {
      row = row.split(' ').filter(value => value !== '');
      if (!row.length) {
        continue;
      }
      for (const value of row) {
        data.setFloat64(index * BYTES_PER_DOUBLE, parseFloat(value));
        index++;
      }
    }

    // ---------- CREATE A GeoidGrid FOR THE GIVEN FILE DATA : ----------

    const dataExtent = new Extent(options.in.crs || 'EPSG:4326', metadata.minX + metadata.stepX / 2, metadata.maxX - metadata.stepX / 2, metadata.minY + metadata.stepY / 2, metadata.maxY - metadata.stepY / 2);
    const dataStep = new THREE.Vector2(metadata.stepX, metadata.stepY);
    return Promise.resolve(new GeoidGrid(dataExtent, dataStep, (verticalIndex, horizontalIndex) => data.getFloat64((metadata.nColumns * verticalIndex + horizontalIndex) * BYTES_PER_DOUBLE)));
  }
};