Transparency, multi-layer

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San Francisco Bay Area- almost all layers selected
San Francisco Bay Area- almost all layers selected

Multi-layer transparency is a new feature in World Wind 1.3.3, and it is 'a doozie,' as my grandmother used to say. This page is begun with great intentions, but for now we will start with some basics.

This is very busy - all layers
This is very busy - all layers

Contents

Introduction

Seattle area multi-layer transparency-midlevel view
Seattle area multi-layer transparency-midlevel view

World Wind is a lot of things to a lot of different people. Some just like to zoom (once there was a page on this topic, but you'll just have to trust us on this), while others want to spin. Many of us focus on the scientific capabilities of World Wind (which are truly impressive), but most people probably mainly just want to zoom (there's that 'zoom' thing again).

But one use of World Wind has probably rarely crossed the average user's mind. Well, make that at least two related uses. The first (and unusual) use would be that of a canvas, allowing the informed and artistically-inclined user to 'paint' his or her very own worlds/maps, etc. The second (and very much related, but likely also more apparent) is the use of WW for actual cartographic purposes. With multi-layer transparency, these uses for WW become very accessible, even to the novice.


Why is this important?

Seattle area multi-layer transparency-closer view
Seattle area multi-layer transparency-closer view


This feature opens up many new possibilities for using World Wind as more than just a viewer.

Here are some recently submitted hotspots I posted with transparency info contained in the images:

Hawaii-1 Spain Sahara Hawaii-2 California

Please come back again soon so we can give you more examples and ideas.

What is multi-layer transparency?

Overview- NLT, Topo, Digital (B&W) ortho -nice colorful blend with all layers contributing meaningfully
Overview- NLT, Topo, Digital (B&W) ortho -nice colorful blend with all layers contributing meaningfully

Multi-layer transparency is the ability to set various characteristics and levels of opacity for each layer separately, and to prioritize to some extent the position of individual layers in the transparency 'stack'. Layers are blended with those above and below, creating a complex view of different data types. It is also known as alpha compositing, or alpha blending.

How does multi-layer transparency work?

zoomed view - this blend allows you to see your house-in US areas covered by B&W Digital Ortho
zoomed view - this blend allows you to see your house-in US areas covered by B&W Digital Ortho

Multi-layer transparency works by uh, magic :-). Actually, it utilizes RGB and Alpha channels to blend multiple layers based on chosen settings. It is useful to have some understanding of image blending (or 'compositing'), and alpha channels (see links above), but is by no means necessary for the use of this relatively easy and very powerful feature of World Wind.

Here are links to some discussions on the technical side of things- I will at some point attempt to translate these concepts into plain English. For now - give a read . . .


To make things easier to get started, I will be posting more (see above) screenshots with relevant settings soon, which will provide you with basic settings for an area, which can then be easily adjusted for similar conditions elsewhere. Stay tuned!

Where and how do I adjust the settings?

although this is an area with urban ortho coverage, this would be one way of 'faking it' from most elevations
although this is an area with urban ortho coverage, this would be one way of 'faking it' from most elevations
  • In World Wind 1.3.3, click View and select Layer manager.
  • With Layer manager open, click on each main heading, exposing submenus. Any submenus within these will show up with arrows to the left of the layer name - click those to expand submenus completely. Each name which does not have an arrow to its left may be considered a layer for this discussion. Right click on the layer you wish to adjust settings for, and then click Properties. A dialog box will display, witha number of settings. This is what you must play with, until we get better documentation up. Do not worry, layer settings at this point cannot be saved (that will most likely be available in the not-too-distant future), and they revert back to original settings once that layer (or WW) is turned off. Therefore, you can mess with these all you want, and it won't hurt your settings . . .

Who can help me, since I can't get it to work?

A simple color-blended and terrain-mapped topographic map- very useful!
A simple color-blended and terrain-mapped topographic map- very useful!

You can try IRC, or the forums- this is a new feature in WorldWind, and most people are probably not very familiar with it yet. Also, it if doesn't work, there may be an issue with your video card . . .

Keep in mind also that these settings are provided as guidelines, and may not produce exactly the same results on your system, depending on video/etc. However, if you take your time and work out several of the examples, it should give you enough familiarity with how your system responds to various settings, and then you could adjust accordingly. Also VERY IMPORTANT - location is key. These settings are not likely to produce optimal results anywhere other than the specific place where they were originally made. Even if the terrain/groundcover, etc appears the same, there are many factors which can affect blending. To find location, look to upper right corner.

When is this documentation going to be done?

Very good question. Maybe never. But it is being worked on currently. And will be worked on some more soon.

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