谷歌KML GX：DRAWORDER

Question

<?xml version="1.0" encoding="UTF-8"?> 
<kml 
    xmlns="http://www.opengis.net/kml/2.2" 
    xmlns:gx="http://www.google.com/kml/ext/2.2"> 

    <Document> 

    <Style id="Line1"> 
     <LineStyle> 
     <color>ffff0000</color> 
     <width>4</width> 
     </LineStyle> 
    </Style> 
    <Style id="Line2"> 
     <LineStyle> 
     <color>ff00ff00</color> 
     <width>4</width> 
     </LineStyle> 
    </Style> 
    <Style id="Poly1"> 
     <PolyStyle> 
     <color>ff0000ff</color> 
     </PolyStyle> 
    </Style>  
    <Style id="Poly2"> 
     <PolyStyle> 
     <color>ffffffff</color> 
     </PolyStyle> 
    </Style> 



    <Placemark> 
     <name>Line 1</name> 
     <styleUrl>#Line1</styleUrl> 
     <LineString> 
     <coordinates> 
      -112.265654928602,36.09447672602546,2357 
      -112.2660384528238,36.09342608838671,2357 
      -112.2668139013453,36.09251058776881,2357 
      -112.2677826834445,36.09189827357996,2357 
      -112.2688557510952,36.0913137941187,2357 
      -112.2694810717219,36.0903677207521,2357 
      -112.2695268555611,36.08932171487285,2357 
      -112.2690144567276,36.08850916060472,2357 
      -112.2681528815339,36.08753813597956,2357 
      -112.2670588176031,36.08682685262568,2357 
      -112.2657374587321,36.08646312301303,2357 
     </coordinates> 
     <gx:drawOrder>2</gx:drawOrder> 
     </LineString> 
    </Placemark> 

    <Placemark> 
     <name>Polygon 1</name> 
     <styleUrl>#Poly1</styleUrl> 
     <Polygon> 
     <outerBoundaryIs> 
      <LinearRing> 
      <coordinates> 
       -112.265654928602,36.09447672602546,2357 
       -112.2660384528238,36.09342608838671,2357 
       -112.2668139013453,36.09251058776881,2357 
       -112.2677826834445,36.09189827357996,2357 
       -112.2688557510952,36.0913137941187,2357 
       -112.2694810717219,36.0903677207521,2357 
       -112.2695268555611,36.08932171487285,2357 
       -112.2690144567276,36.08850916060472,2357 
       -112.2681528815339,36.08753813597956,2357 
       -112.2670588176031,36.08682685262568,2357 
       -112.2657374587321,36.08646312301303,2357 
      </coordinates> 
      </LinearRing> 
     </outerBoundaryIs> 
     <gx:drawOrder>4</gx:drawOrder> 
     </Polygon> 
    </Placemark> 

    <Placemark> 
     <name>Line 2</name> 
     <styleUrl>#Line2</styleUrl> 
     <LineString> 
     <coordinates> 
      -112.265654928602,36.09447672602546,2357 
      -112.2660384528238,36.09342608838671,2357 
      -112.2668139013453,36.09251058776881,2357 
      -112.2677826834445,36.09189827357996,2357 
      -112.2688557510952,36.0913137941187,2357 
      -112.2694810717219,36.0903677207521,2357 
      -112.2695268555611,36.08932171487285,2357 
      -112.2690144567276,36.08850916060472,2357 
      -112.2681528815339,36.08753813597956,2357 
      -112.2670588176031,36.08682685262568,2357 
      -112.2657374587321,36.08646312301303,2357 
     </coordinates> 
     <gx:drawOrder>4</gx:drawOrder> 
     </LineString> 
    </Placemark> 

    <Placemark> 
     <name>Polygon 2</name> 
     <styleUrl>#Poly2</styleUrl> 
     <Polygon> 
     <outerBoundaryIs> 
      <LinearRing> 
      <coordinates> 
       -112.265654928602,36.09447672602546,2357 
       -112.2660384528238,36.09342608838671,2357 
       -112.2668139013453,36.09251058776881,2357 
       -112.2677826834445,36.09189827357996,2357 
       -112.2688557510952,36.0913137941187,2357 
       -112.2694810717219,36.0903677207521,2357 
       -112.2695268555611,36.08932171487285,2357 
       -112.2690144567276,36.08850916060472,2357 
       -112.2681528815339,36.08753813597956,2357 
       -112.2670588176031,36.08682685262568,2357 
       -112.2657374587321,36.08646312301303,2357 
      </coordinates> 
      </LinearRing> 
     </outerBoundaryIs> 
     <gx:drawOrder>8</gx:drawOrder> 
     </Polygon> 
    </Placemark> 

    </Document> 
</kml> 

所以你可以在上面KML我試圖使用GX看到：DRAWORDER元素的行字符串&多邊形分類到繪圖層。但是，如果您在kml interactive sampler甚至Google地球（免費桌面版）中加載該數據，幾何圖元只能按照「類似圖元」的順序排序。也就是說，線串僅針對其他線串進行排序，並且多邊形僅針對其他多邊形排序。

在這種情況下，您可以看到「第1行」和「第2行」的繪製順序爲<「Polygon 2」&因此我期望「多邊形2」能夠繪製所有內容的頂部。但事實並非如此。最後，我不得不使用高度值來實現我想要的z順序，但這是一個令人不滿意的解決方案，因爲大多數人使用等軸測投影來查看kml幾何。高度值導致我的幾何體傾斜。

我想知道的是：

1. 這是GX的預期行爲：DRAWORDER？元素周圍的文檔是稀疏的&它甚至說它只適用於線串，但根據xsd是應該適用於所有幾何圖元（它看起來好像......至少對於多邊形以及無論如何...）

2. 有沒有辦法讓gx：drawOrder適用於所有 幾何圖元？

在此先感謝！

Answer 1

KML documentation僅針對線串而不是多邊形提及<gx:drawOrder>，也沒有提及跨越不同幾何形狀（線，環和多邊形）的drawOrder的行爲。對Polygons的drawOrder支持沒有記錄，但在bug追蹤器中報告爲issue。

您自然希望drawOrder在所有幾何圖元上都一樣，但看起來像Google地球按類型繪製特徵：多邊形，然後是地面疊加，然後是線條和點數據，其中drawOrder僅適用於一個小組。 ScreenOverlays是最後繪製的，所以它們始終位於最前面。

這意味着drawOrder = 2的多邊形與drawOrder = 1的線重疊，仍然會在該線下顯示多邊形。此外，即使多邊形的drawOrder值較高並與GroundOverlay（又稱圖像疊加）重疊，該多邊形也會首先被繪製並隱藏在GroundOverlay下。

gx：DrawOrder不是OGC KML 2.2標準的一部分。這是一個Google KML Extension，所以Google定義了它的工作原理。也意味着Google可以改變它的工作方式。