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Convert a thermal orthomosaic to JPEG using QGIS
Convert a thermal orthomosaic to JPEG using QGIS
Updated over a week ago

Orthomosaics you download from the platform are always stored as GeoTIFFs with a .tif extension. This format allows us to store the geographical information of the orthomosaic. For thermal orthomosaics specifically, it also stores the raw temperature data we get from the drones. This way, you have access to all data.

In some cases however, it's useful to convert the file to a JPEG or PNG as you don't need any special software to read it. A GeoTIFF file looks almost black when you open with regular software. This is because it contains a very wide range of temperature values. To properly create a visual representation, we have to "render" the orthomosaic with a certain color palette and thermal range. QGIS is a free open-source application that can handle geo-spatial data like our orthomosaics, so we can use that to convert the files.

Quick tip: if you just want to share a small part of the orthomosaic, it's usually easiest to configure the Sitemark map to your liking and take a screenshot.

Download QGIS

If you don't have QGIS yet, you can download it here.

Download the Orthomosaic

Go to the operation you want to download the orthomosaic from and use the export functionality to download the file. You can find it under Export > Data on the top right of the screen.

Open the Orthomosaic in QGIS

Next, open the orthomosaic in QGIS by dropping the file on QGIS, or by going to Layer > Add Layer > Add Raster Layer... and selecting the orthomosaic file.

QGIS right after dropping in the thermal orthomosaic

Apply a Color Palette

The orthomosaic will look a bit funky, because QGIS doesn't know how to color it. Every thermal orthomosaic has two "bands", one for the temperature values and one for the transparency (also called the alpha band).

Double click on the layer on the bottom left of the screen to open the Properties window, or right click on the layer and select Properties...

Configure layer properties in QGIS

In the Symbology section, change the render type to "Singleband pseudocolor" and make sure Band 1 (Gray) is selected.

Then change the Min and Max values to somewhere around 7400 and 8000. You can play with these values to get the right thermal range. This support article also explains how to use the histogram to select these values.

If you want, you can select a different Color ramp to use a different color palette. We typically advise the Magma palette for thermal orthomosaics.

Configure Symbology of a layer in QGIS

Finally, go to the Transparency section and under Custom Transparency Options, change the Transparency band to Band 2. This will make sure you don't have a black background behind the orthomosaic.

Configure Transparency of a layer in QGIS

Click OK. Your orthomosaic should now look something like this:

View of a properly configured thermal orthomosaic in QGIS

Export the Orthomosaic

The final step is to export the orthomosaic. To do that, go to Project > Import/Export > Export Map to Image...

In the extent section, select the Calculate from Layer option and select your orthomosaic layer (most likely called output as that's the file name you get from the platform).

Configuring the export extent in QGIS

Now change the resolution of the image to something like 300dpi. You can play with this value to increase or decrease the resolution.

Now hit Save, fill in a file name, pick a format and say where you want to save the image. The output should look like the map you see in QGIS.

Tips & Tricks

You can play with the following settings to change the image to your liking:

  • The color palette, including the min, max and color ramp settings.

  • The extent you're exporting. You can zoom in to a part of the map if you don't want to export everything.

  • The resolution of the export. Increasing the resolution will increase the file size of course. Especially for large maps this might be a problem.

  • The output format. PNG typically looks better than JPEG because it uses lossless compression, but the files will be bigger.

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