Drilling thru cement floor with radiant heat flow below
A thermal imaging camera will be able to pinpoint the location of the pipes, I have a flir camera that attaches to my phone it will even show wiring that has bad connections they cost around 200 and up and are a great troubleshooting tool for a DIY person. I have used my camera to find leaks where I could not detect water from the roof until it ran down a wall and made a wet spot on sheetrock. I have used it for sealing up duct work, and for electrical inspections. Finding the location of the radient pipe work would be another great use for this tool. When the heat is running you would take a image and the hot zone will be where the pipe is. Based on the work I have used my camera for I believe you could pinpoint your pipes within a 1/4" or even closer depending on how thick the concrete is above the pipe.