Skew

kfirbene · December 31, 2018, 2:44pm

Hi,

I wanted know if Cesium has an API that handles camera skew?

I want to create application that the camera is steady at one position, but changes the look angle(skew).

**Thanks. **

omar · January 2, 2019, 9:55pm

If I understand you correctly, then yes, you can alter the camera angle while keeping its position constant. You might be interested in the camera “look”, “twist” and “rotate” functions described here:

Let me know if that helps. What kind of application are you making?

kfirbene · January 3, 2019, 9:28am

Hi,

No this is what I am looking for, Just came across an API that might help:

Cesium.PerspectiveFrustum

Thanks.

kfirbene · January 3, 2019, 2:17pm

Still facing this question, I will explain in more details.
I need to set the camera to look, at a certain perspective, on a location with an asymmetric frustum.

Is there a way to define asymmetric frustum?

omar · January 3, 2019, 2:45pm

I haven’t done this before, but I think in theory you should be able to with minimal change to the source code. I think you’d need to define a custom frustrum, here is how the default one is defined:

github.com

CesiumGS/cesium/blob/master/Source/Core/PerspectiveFrustum.js

import Check from './Check.js';
import defaultValue from './defaultValue.js';
import defined from './defined.js';
import DeveloperError from './DeveloperError.js';
import CesiumMath from './Math.js';
import PerspectiveOffCenterFrustum from './PerspectiveOffCenterFrustum.js';

    /**
     * The viewing frustum is defined by 6 planes.
     * Each plane is represented by a {@link Cartesian4} object, where the x, y, and z components
     * define the unit vector normal to the plane, and the w component is the distance of the
     * plane from the origin/camera position.
     *
     * @alias PerspectiveFrustum
     * @constructor
     *
     * @param {Object} [options] An object with the following properties:
     * @param {Number} [options.fov] The angle of the field of view (FOV), in radians.
     * @param {Number} [options.aspectRatio] The aspect ratio of the frustum's width to it's height.
     * @param {Number} [options.near=1.0] The distance of the near plane.

This file has been truncated. show original

This is where the Scene initializes the new camera:

github.com

CesiumGS/cesium/blob/master/Source/Scene/Scene.js#L774


canvas : {
    get : function() {
        return this._canvas;
    }
},


/**
 * The drawingBufferHeight of the underlying GL context.
 * @memberof Scene.prototype
 *
 * @type {Number}
 * @readonly
 *
 * @see {@link https://www.khronos.org/registry/webgl/specs/1.0/#DOM-WebGLRenderingContext-drawingBufferHeight|drawingBufferHeight}
 */
drawingBufferHeight : {
    get : function() {
        return this._context.drawingBufferHeight;
    }
},

I think you’ll need to add an option there to allow it to pass a custom frustum, so that it would use it here instead of the default one:

thttps://github.com/AnalyticalGraphicsInc/cesium/blob/master/Source/Scene/Scene.js#L774

I hope that helps. I’d love to know what kind of application you’re building with this that requires an asymmetric frustum. If it’s something others can use as well it might be someting that CesiumJS could expose.