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Posts Tagged ‘Tutorials’

Google Earth Skydome Using PhotoOverlay

September 23rd, 2007 2 comments

Sky in Google Earth using PhotoOverlayA few months ago I posted a Google Earth add-on which used a large 3D model hemisphere with a full-sky cloud image plastered on the inside to create fake sky backdrops.  Turns out, with a little bit of KML magic you can do pretty much the same thing with the new panoramic Photo Overlay feature in Google Earth 4.2.

This is a PhotoOverlay sky centred on the Swiss Alps:

PhotoOverlay Skydome (30kB)  

Opening the file takes you straight inside the panorama. When you click ‘exit photo’ the dome remains visible, enabling you to fly around the inside the same way as the 3D model version.  If you move too far away from the dome it disappears, replaced by an Icon. Double click on this Icon or the label under the ‘Places’ panel to re-enter it.

Compared with my 3D model version this has the advantage of being very quick to put together from scratch. The key is to use a very large spherical Photo Overlay, with a field of view covering just the top half and Camera altitude set at, or very near ground level. Here’s the KML stripped to its basics:

<?xml version=”1.0″ encoding=”UTF-8″?>
<kml xmlns=”http://earth.google.com/kml/2.2″>
<PhotoOverlay>
  <Camera>
     <longitude>8.230</longitude>
     <latitude>46.707</latitude>
     <altitude>100</altitude>
     <heading>0</heading>
     <tilt>90</tilt>
     <roll>0</roll>   
  </Camera>
  <Icon>
  <href>files/clouds.jpg</href>
  </Icon>
  <ViewVolume>
   <leftFov>-180</leftFov>
   <rightFov>180</rightFov>
   <bottomFov>0</bottomFov>
   <topFov>90</topFov>
   <near>20000</near>
  </ViewVolume>
  <Point>
   <altitudeMode>relativetoGround</altitudeMode>
   <coordinates>8.230, 46.707, 0</coordinates>
  </Point>
  <shape>sphere</shape>
  <roll>0</roll>
</PhotoOverlay>
</kml>

  • The <ViewVolume> attributes tell GE what proportion of the sphere to display.  A complete sphere would have a <bottomFov> value of -90.  Here I just want the top half so I set this to 0.
  • The radius of the sky dome is given by the <near> value.   20,000 metres in this case.  Note, if this value is too large, GE won’t fully render it.
  • On mountainous terrain the <Camera> altitude is tricky to get right.  Too low and GE finds it impossible to fly inside to view the panorama in photo-mode. Too high and there’s a visible gap between dome and the ground.
  • The <Point> coordinates aren’t absolutely necessary, but do ensure there’s an Icon when the dome itself isn’t visible, which is useful. 

For the image you need a 360 degree panoramic cloud photo.  The one in this file is an equirectangular image (sky12.jpg) from Philo’s Sky Collection. I chopped off the bottom half of the original and reduced it 1024 pixels wide.  High resolution images would need splitting into smaller tiles and the creation of an <ImagePyramid>. For further info check out the new KML topics documentation here: http://code.google.com/apis/kml/documentation/topicsinkml.html

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Editing Google Earth

July 29th, 2007 No comments

London Eye - Blue ThamesIn the previous post I mentioned that my London Eye animation needed tweaking because of a colour change in Google Earth’s London aerial photos.  I’ve now fixed the file.

The issue occurred because the file masks GE’s imagery with a ‘photoshopped’ version of itself.  I did this to remove the aerial shot of the London Eye from the scene and clear the way for the animated shadow.

OK, so it’s probably not the most useful thing you can do in Google Earth  but here’s a quick overview of the method I used: 

  • In Google Earth (or Maps) save an image of the area you want to alter.  It makes things easier if the view is pointing directly downwards and due north. 
  • Edit this screenshot in photo/image editing software.   In this case  I just used GIMP‘s clone stamp tool,  and copied other bits of the imagery – mainly river – to cover those parts I wanted hiding.
  • Back in GE return to the place where you took the screen capture.
  • Add Image OverlayClick ‘add image overlay’ and open the edited photo.
  • By dragging the green boundary lines you can accurately stretch and shrink the overlay to the correct location. 
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Textured Globe Models in SketchUp

June 8th, 2007 6 comments

Textured Globe in SketchUpOne of the things I plan to do with this blog is put up some descriptions and tutorials of how I create my files. 

This is something a few people have asked about – texture wrapped globes in SketchUp,  just as I used for my ‘Bouncing Google Earth’ model.   

As its primary use is for architectural modeling, SketchUp doesn’t have any texture wrap options. So rather than attempt to apply a material to every plane surface of a model sphere by hand (very time consuming!) , the simplest thing to do is use object-based 3d modeling software and import the model in.

The following tutorial uses Anim8or  (Freeware, Windows only – sorry) – download from here – much quicker to learn for a task like this than more elaborate software like blender. 

The global map image used for texturing needs to be in what’s known as ‘equidistant cylindrical projection’,  more commonly called a ‘cylindrical map’.   There are hundreds of these across Nasa’s website and elsewhere on the web.  For Earth as well as other planets.

Earth Map

In this example I use the January Blue Marble image from here.

Read more…

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