@giro3d/giro3d/src/formats/bilWorker.ts

A JS/WebGL framework for 3D geospatial data visualization

import type { BaseMessageMap, Message, SuccessResponse } from '../utils/WorkerPool';
import { createErrorResponse } from '../utils/WorkerPool';

export type DecodeBilTerrainResult = { data: ArrayBuffer; min: number; max: number };

export function decodeRaster(bil: Float32Array, noData?: number): DecodeBilTerrainResult {
    let min = +Infinity;
    let max = -Infinity;

    const data = new Float32Array(bil.length * 2); // For alpha channel;

    // NOTE for BIL format, we consider everything that is under noDataValue as noDataValue
    // this is consistent with the servers behaviour we tested but if you see services that
    // expects something different, don't hesitate to question the next loop
    for (let i = 0; i < bil.length; i++) {
        const value = bil[i];

        if (noData != null && value <= noData) {
            data[i * 2 + 0] = 0; // Elevation at zero by default
            data[i * 2 + 1] = 0; // Transparent pixel because no-data
        } else {
            data[i * 2 + 0] = value;
            data[i * 2 + 1] = 1;
            min = Math.min(value, min);
            max = Math.max(value, max);
        }
    }

    return { data: data.buffer, min, max };
}

// Web worker implementation

type DecodeBilTerrainRequest = { buffer: ArrayBuffer; noData?: number };
export type DecodeBilTerrainMessage = Message<DecodeBilTerrainRequest>;
export type DecodeBilTerrainMessageResponse = SuccessResponse<DecodeBilTerrainResult>;

export type MessageType = 'DecodeBilTerrainMessage';

export interface MessageMap extends BaseMessageMap<MessageType> {
    DecodeBilTerrainMessage: {
        payload: DecodeBilTerrainRequest;
        response: DecodeBilTerrainResult;
    };
}

onmessage = function onmessage(ev: MessageEvent<DecodeBilTerrainMessage>) {
    const message = ev.data;

    try {
        if (message.type === 'DecodeBilTerrainMessage') {
            const result = decodeRaster(
                new Float32Array(message.payload.buffer),
                message.payload.noData,
            );
            const response: DecodeBilTerrainMessageResponse = {
                requestId: message.id,
                payload: result,
            };
            this.postMessage(response, { transfer: [response.payload.data] });
        }
    } catch (err) {
        this.postMessage(createErrorResponse(message.id, err));
    }
};