java - WorldWind 点地标航向

Question

在 NASA WorldWind Java 中，我使用 PointPlacemark 来表示图像，因为无论缩放级别如何，它都保持相同的大小。问题是我想在 Point Placemark 上设置航向，即使相机倾斜，它也会保持在那个罗盘航向上。当我查看一个倾斜的地球时，它的工作原理与我想要的完全一样，但是当我倾斜时，地标继续面向屏幕而不是与地球一起倾斜，这导致它表现得很奇怪。

这是一张 GIF 图像，展示了我所看到的:https://giphy.com/embed/3o7WIqZUceR8xh6BOg

我希望点地标图像保持在相对于地球的方向上，即使在倾斜时也是如此——因此图像在 View 倾斜时基本上是“扁平化”的，同时无论缩放级别如何仍保持相同的大小。

这是我正在使用的代码片段。我正在设置 attrs.setHeadingReference(AVKey.RELATIVE_TO_GLOBE);在关联的 PointPlacemarkAttributes 上。在此示例中，我将航向设置为 135 度。

import gov.nasa.worldwind.WorldWind;
import gov.nasa.worldwind.avlist.AVKey;
import gov.nasa.worldwind.geom.Position;
import gov.nasa.worldwind.layers.RenderableLayer;
import gov.nasa.worldwind.render.Offset;
import gov.nasa.worldwind.render.PointPlacemark;
import gov.nasa.worldwind.render.PointPlacemarkAttributes;

public class Placemarks extends ApplicationTemplate {
    public static class AppFrame extends ApplicationTemplate.AppFrame {

        public AppFrame() {
            super(true, true, false);

            final RenderableLayer layer = new RenderableLayer();

            PointPlacemark pp = new PointPlacemark(Position.fromDegrees(28, -102, 30000));
            pp.setLabelText("Airplane");
            pp.setLineEnabled(false);
            pp.setAltitudeMode(WorldWind.ABSOLUTE);
            PointPlacemarkAttributes attrs = new PointPlacemarkAttributes();
            attrs.setImageAddress("images/airplane.png");
            attrs.setScale(0.05);
            attrs.setImageOffset(Offset.CENTER);

            //Point to 135.0
            attrs.setHeading(135.0);
            attrs.setHeadingReference(AVKey.RELATIVE_TO_GLOBE);

            pp.setAttributes(attrs);

            layer.addRenderable(pp);

            // Add the layer to the model.
            insertBeforeCompass(getWwd(), layer);
        }
    }

    public static void main(String[] args) {
        ApplicationTemplate.start("WorldWind Placemarks", AppFrame.class);
    }

}

我还尝试过使用应用了纹理的多边形。它的定向方式正是我要寻找的——除了我希望图标保持相同大小而不管缩放级别如何(就像 PointPlacemark 所做的那样)。

这是一张 GIF，展示了我在使用多边形时看到的情况。注意本地球倾斜时它是如何工作的:https://giphy.com/embed/xThta4USlDzd8Ii5ZS

这是我为多边形使用的来源:

import java.awt.geom.AffineTransform;
import java.util.Arrays;
import java.util.List;

import gov.nasa.worldwind.WorldWind;
import gov.nasa.worldwind.geom.Position;
import gov.nasa.worldwind.layers.RenderableLayer;
import gov.nasa.worldwind.render.BasicShapeAttributes;
import gov.nasa.worldwind.render.Polygon;

public class TexturedPolygon extends ApplicationTemplate {

    public static Polygon createPolygonTexturedImage(String filePath, Position pos, double heading, double scale) {

        double offsetDist = 1.0D * scale;

        Position p1 = Position.fromDegrees(pos.getLatitude().addDegrees(-offsetDist).getDegrees(),
                pos.getLongitude().addDegrees(-offsetDist).getDegrees(), pos.getAltitude());
        Position p2 = Position.fromDegrees(pos.getLatitude().addDegrees(offsetDist).getDegrees(),
                pos.getLongitude().addDegrees(-offsetDist).getDegrees());
        Position p3 = Position.fromDegrees(pos.getLatitude().addDegrees(offsetDist).getDegrees(),
                pos.getLongitude().addDegrees(offsetDist).getDegrees());
        Position p4 = Position.fromDegrees(pos.getLatitude().addDegrees(-offsetDist).getDegrees(),
                pos.getLongitude().addDegrees(offsetDist).getDegrees());

        double[] points = new double[] { p1.getLatitude().getDegrees(), p1.getLongitude().getDegrees(),
                p2.getLatitude().getDegrees(), p2.getLongitude().getDegrees(), p3.getLatitude().getDegrees(),
                p3.getLongitude().getDegrees(), p4.getLatitude().getDegrees(), p4.getLongitude().getDegrees() };

        double[] transformedPoints = new double[8];
        AffineTransform rotation = new AffineTransform();
        rotation.rotate(Math.toRadians(heading), pos.getLatitude().getDegrees(), pos.getLongitude().getDegrees());
        rotation.transform(points, 0, transformedPoints, 0, 4);

        double altitude = pos.getAltitude();
        p1 = Position.fromDegrees(transformedPoints[0], transformedPoints[1], altitude);
        p2 = Position.fromDegrees(transformedPoints[2], transformedPoints[3], altitude);
        p3 = Position.fromDegrees(transformedPoints[4], transformedPoints[5], altitude);
        p4 = Position.fromDegrees(transformedPoints[6], transformedPoints[7], altitude);

        List<Position> positions = Arrays.asList(p1, p2, p3, p4);
        Polygon polygon = new Polygon(positions);
        polygon.setAltitudeMode(WorldWind.ABSOLUTE);

        BasicShapeAttributes mattr = new BasicShapeAttributes();
        mattr.setDrawOutline(false);
        mattr.setDrawInterior(true);
        polygon.setAttributes(mattr);
        polygon.setTextureImageSource(filePath, new float[] { 0.0F, 0.0F, 1.0F, 0.0F, 1.0F, 1.0F, 0.0F, 1.0F }, 4);

        return polygon;
    }

    public static class AppFrame extends ApplicationTemplate.AppFrame {
        public AppFrame() {
            super(true, true, false);

            final RenderableLayer layer = new RenderableLayer();

            Position pos = Position.fromDegrees(28, -102, 30000);
            String url = "images/airplane.png";

            layer.addRenderable(createPolygonTexturedImage(url, pos, 135.0, 1.05));

            // Add the layer to the model.
            insertBeforeCompass(getWwd(), layer);
        }
    }

    public static void main(String[] args) {
        ApplicationTemplate.start("WorldWind Placemarks", AppFrame.class);
    }

}

为了完整起见——这是我用作 airplane.png 的图像:

总而言之，我正在寻找的是:

• 由图标图像表示的可渲染
• 无论缩放级别如何，图标都保持相同大小
• 即使相机 View 倾斜，图标也会保持在地球罗盘方向上

Answer 1

通过结合这个 question 的解决方案以及将屏幕倾斜与俯仰联系起来的 CompassLayer 逻辑。

将此方法添加到 PointPlacemark.java(取自 CompassLayer):

protected double computePitch(View view)
{
    if (view == null)
        return 0.0;

    if (!(view instanceof OrbitView))
        return 0.0;

    OrbitView orbitView = (OrbitView) view;
    return orbitView.getPitch().getDegrees();
}

然后在 doDrawOrderedRenderable(DrawContext dc, PickSupport pickCandidates, OrderedPlacemark opm) 方法中，使用以下逻辑:

protected void doDrawOrderedRenderable(DrawContext dc, PickSupport pickCandidates, OrderedPlacemark opm)
{
    if (this.isDrawLine(dc, opm))
        this.drawLine(dc, pickCandidates, opm);

    if (this.activeTexture == null)
    {
        if (this.isDrawPoint(dc))
            this.drawPoint(dc, pickCandidates, opm);
        return;
    }

    GL2 gl = dc.getGL().getGL2(); // GL initialization checks for GL2 compatibility.

    OGLStackHandler osh = new OGLStackHandler();
    try
    {
        if (dc.isPickingMode())
        {
            // Set up to replace the non-transparent texture colors with the single pick color.
            gl.glEnable(GL.GL_TEXTURE_2D);
            gl.glTexEnvf(GL2.GL_TEXTURE_ENV, GL2.GL_TEXTURE_ENV_MODE, GL2.GL_COMBINE);
            gl.glTexEnvf(GL2.GL_TEXTURE_ENV, GL2.GL_SRC0_RGB, GL2.GL_PREVIOUS);
            gl.glTexEnvf(GL2.GL_TEXTURE_ENV, GL2.GL_COMBINE_RGB, GL2.GL_REPLACE);

            Color pickColor = dc.getUniquePickColor();
            pickCandidates.addPickableObject(this.createPickedObject(dc, pickColor));
            gl.glColor3ub((byte) pickColor.getRed(), (byte) pickColor.getGreen(), (byte) pickColor.getBlue());
        }
        else
        {
            gl.glEnable(GL.GL_TEXTURE_2D);
            Color color = this.getActiveAttributes().getImageColor();
            if (color == null)
                color = PointPlacemarkAttributes.DEFAULT_IMAGE_COLOR;
            gl.glColor4ub((byte) color.getRed(), (byte) color.getGreen(), (byte) color.getBlue(),
                (byte) color.getAlpha());
        }

        // This was relocated from the check in version.
        // Compute the scale
        double xscale;
        Double scale = this.getActiveAttributes().getScale();
        if (scale != null)
            xscale = scale * this.activeTexture.getWidth(dc);
        else
            xscale = this.activeTexture.getWidth(dc);

        double yscale;
        if (scale != null)
            yscale = scale * this.activeTexture.getHeight(dc);
        else
            yscale = this.activeTexture.getHeight(dc);
        double maxwh = Math.max(xscale, yscale);

        // The image is drawn using a parallel projection.
        // This came from the fix in https://stackoverflow.com/questions/49637844/worldwind-pointplacemark-pitch
        osh.pushProjectionIdentity(gl);
        gl.glOrtho(0d, dc.getView().getViewport().width, 0d, dc.getView().getViewport().height, -0.6 * maxwh, 0.6 * maxwh);

        // Apply the depth buffer but don't change it (for screen-space shapes).
        if ((!dc.isDeepPickingEnabled()))
            gl.glEnable(GL.GL_DEPTH_TEST);
        gl.glDepthMask(false);

        // Suppress any fully transparent image pixels.
        gl.glEnable(GL2.GL_ALPHA_TEST);
        gl.glAlphaFunc(GL2.GL_GREATER, 0.001f);

        // Adjust depth of image to bring it slightly forward
        double depth = opm.screenPoint.z - (8d * 0.00048875809d);
        depth = depth < 0d ? 0d : (depth > 1d ? 1d : depth);
        gl.glDepthFunc(GL.GL_LESS);
        gl.glDepthRange(depth, depth);

        // The image is drawn using a translated and scaled unit quad.
        // Translate to screen point and adjust to align hot spot.
        osh.pushModelviewIdentity(gl);
        gl.glTranslated(opm.screenPoint.x + this.dx, opm.screenPoint.y + this.dy, 0);

        Double heading = getActiveAttributes().getHeading();
        Double pitch =          this.computePitch(dc.getView());

        // Adjust heading to be relative to globe or screen
        if (heading != null)
        {
            if (AVKey.RELATIVE_TO_GLOBE.equals(this.getActiveAttributes().getHeadingReference()))
                heading = dc.getView().getHeading().degrees - heading;
            else
                heading = -heading;
        }

        // Apply the heading and pitch if specified.
        if (heading != null || pitch != null)
        {
            gl.glTranslated(xscale / 2, yscale / 2, 0);
            if (pitch != null)
                gl.glRotated(pitch, 1, 0, 0);
            if (heading != null)
                gl.glRotated(heading, 0, 0, 1);
            gl.glTranslated(-xscale / 2, -yscale / 2, 0);
        }

        // Scale the unit quad
        gl.glScaled(xscale, yscale, 1);

        if (this.activeTexture.bind(dc))
            dc.drawUnitQuad(activeTexture.getTexCoords());

        gl.glDepthRange(0, 1); // reset depth range to the OGL default

        if (this.mustDrawLabel())
        {
            if (!dc.isPickingMode() || this.isEnableLabelPicking())
                this.drawLabel(dc, pickCandidates, opm);
        }
    }
    finally
    {
        if (dc.isPickingMode())
        {
            gl.glTexEnvf(GL2.GL_TEXTURE_ENV, GL2.GL_TEXTURE_ENV_MODE, OGLUtil.DEFAULT_TEX_ENV_MODE);
            gl.glTexEnvf(GL2.GL_TEXTURE_ENV, GL2.GL_SRC0_RGB, OGLUtil.DEFAULT_SRC0_RGB);
            gl.glTexEnvf(GL2.GL_TEXTURE_ENV, GL2.GL_COMBINE_RGB, OGLUtil.DEFAULT_COMBINE_RGB);
        }

        gl.glDisable(GL.GL_TEXTURE_2D);
        osh.pop(gl);
    }
}

它看起来像这样: