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I have two rasters who correspond to the same place, one is a thermal orthomosaic and the other is a DEM, because each one was done with different cameras (the thermal cameras have low resolution) the cell size is different.

The rasters are georeferenced.

How could I work with these two rasters?

My intention is compute the height and the temperature at the same time adding an equation with the raster calculator, this means the cells need to have the same size and be in the same position.

Which is the tool in ArcGIS for that?

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There are a couple of ways you could approach this, and in any event, you don't need to have the same cell size for input rasters (DEM and temperature grid). What you want to pay attention to with Raster Calculator is the Environments settings. Specifically, the Output Coordinates information (for reference system and units of output raster), the Processing Extent (the area you want represented), and most importantly the Raster Analysis - in these drop-down options, you can set your cell size for the output raster. The default is maximum of inputs, which means whichever raster layer has the coarsest resolution will be set for your output (if you don't set anything).

Let's say your temperature raster has 30 meter resolution, and your DEM has 10 meter resolution (for example, it might be reversed). If set the "Raster Analysis" Cell Size to 10 in Environments, and perform a calculation, that calculation will be performed for every DEM cell and respective value, against the temperature value for the larger cell. Your output raster will be 10 meters, and each 30 meter temperature value will have been computed with 9 different elevations.

The calculator doesn't require matching resolutions, it simply works based on XY overlap, and for each cell in the output what values are represented in that location by the respective input layers.

As a complete alternative, if you want you can create vector points, and run an Extract Multi Values tool - this would allow you to create attributes for each point based on multiple rasters at the same time. But I think calculator sounds like what you want.

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you can use con tool calculate temp and height together. I assume your DEM ranges in thousands or hundreds and temp is in hundreds or tens.Use con from raster calculator, con(Thermal, Thermal*1,000,000+DEM, Thermal, "Value<=Your Max Thermal Value"). This will give you values 1TTTEEEEE. Then you will need to create a field for temp and use field calculation as Int(Value/100,000). Finally you will create another field and name it as elevation, use field calculator again (Float(Value/100,000)-temp)*10000. So you will have a raster with 3 columns (Value, Temp and Elevation). I have never done this with so many values; you might need to reclassify your raster to go easy with your computer.
As @tweakybiscuit mentioned you can adjust cell size in environment settings. It is located just below the raster calculator tool. There is also an option you can adjust "same as DEM raster" or "same as thermal raster".

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