Query Builder Palette
Posted on 19 Sep 2018
When you work with single-channel images, you need to focus in depth on a narrow range of values and clearly evaluate researched data.
For more accurate analysis of satellite images and evaluation of vegetation indices, the OpenWeather team launched a very useful tool called Query Builder Palette, which is available for operating in the VANE platform.
The Query Builder Palette is a gradient scale with adjustable points and a palette with color settings.
Using this tool, you can collate a color scale with the original value of the bitmap in the range you specify.
Each point matсhs with a numerical value in the section «Position», which corresponds to a specific value in the radiance range of a single-channel band - [0; 1].
You can pick up a color and a value for each point.
Please follow these simple steps to start using Query Builder Palette:
1. Open Query Builder in your browser https://owm.io/sql-viewer
2. Select the data source, for example, s2 (Sentinel-2) on the «From» tab.
3. Select one of the vegetation indices: NDVI, EVI or NDI on the «Presets» tab.
4. Uncheck the "Colors default" check box on the «Color» tab. You will see a gradient scale.
5. Set value in the Position tab for each point and choose a color from the palette for the previously specified value.
6. Click the "Apply" button. Your settings will be applied to the image.
The "Reset" button resets all changes and returns the palette state to the original one.
All selected settings are displayed in the URL address bar of your browser. This URL can be copied and opened in a new tab of the browser or shared with someone - all the configured settings will be displayed.
So, we told you about the main functions of Query Builder Palette and now we invite you to try it yourself.
Let's look at a simple example with vegetation index NDVI.
NDVI can be considered as an image whose theoretical brightness range is [-1;1]. At the same time, the values related to vegetative vegetation are in the range [0.3;0.9]. Since to display single-channel images on the monitor screen are used 256 colors, only a few colors will be used to display the useful part of the range. This will not allow us to visualize in detail the values we are interested in.
However, we have expanded the range of values and as a result, we have the ability to add colors to the color palette displayed single-channel image. Our tool truncates the range of the original bitmap, removing the values [-1;0] (since these values are not needed in our case), but extends the range from [0;1] to the interval [0;255]. That is, in this case, the original "-1 “will be “0”, and the original ”1" will be “255”.
These actions increase the color range to 255. As a result, the range of the original brightness is displayed much better.