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 the researched data.
For more accurate analysis of satellite images and evaluation of vegetation indices, the OpenWeather team launched a very useful tool called the Query Builder Palette, which can operate on the VANE platform.
The Query Builder Palette is a gradient scale with adjustable points and a palette with colour settings.
Using this tool, you can collate a colour scale with the original value of the bitmap in the range you specify.
Each point matсhes with a numeric value in the “Position” section, which corresponds to a specific value in the radiance range of a single-channel band – [0; 1].
You can pick up a colour and a value for each point.
Please follow these simple steps to start using Query Builder Palette:
- Open Query Builder in your browser: https://owm.io/sql-viewer.
- Select the data source – for example, s2 (Sentinel-2) – on the “From” tab.
- Select one of the vegetation indices, NDVI, EVI or NDI, on the “Presets” tab.
- Uncheck the “Colours default” check box on the “Colour” tab. You will see a gradient scale.
- Set a value in the “Position” tab for each point, and choose a colour from the palette for the value you specified earlier.
- Click the “Apply” button. Your settings will be applied to the image.
The “Reset” button resets all changes and returns the palette to its original state.
All your selected settings are displayed in the URL address bar of your browser. You can copy this URL and open it in a new tab in your browser, or share it with someone – all the configured settings will be displayed.
So, we have told you about the main functions of the Query Builder Palette – and now we invite you to try it yourself.
Let’s look at a simple example with the 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 256 colours are used to display single-channel images on the monitor screen, only a few colours will be used to display the useful part of the range. This will not allow us to visually represent 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 colours to the colour palette displayed in a 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 size of the colour range to 255. As a result, the range of the original brightness is displayed much better.