Before I made some sugestions that could help, I feel comepelled to mention this.
I know it is not for printing, but the reference Ryan is a good reference to see the dimensions.
Sometime ago I was using some geodata from nasa (as a hobby) and the raw information (from the terrain of the heights of the Earth) was 21,000 x 21,000 px in 8 diferent manageable blocks, giving a total of 84,000 x 42,000 px. That is an insane dimension for a normal computer.
Some math on the RAW disk space dimensions on your image.
172,500 x 172,500 = 29,756,250,000 px or 29,756.25 Mpx (More or less a thousand photos on a high resolution camera)
Asuming that you need a 24 bit image (normal RGB image) that is
- 714,150,000,000 bits
- 89,268,750,000 bytes
- 89,268.75 Mb
- 89.26875 Gb
of raw disk space.
The compressed size of an image depends on two things, the compression method and the info the image itself contains. But you need to think beforehand the RAW uncompressed dimension for this kind of work.
You could do that in Photoshop, but you need to max the RAM of your computer. It is recomended that you has the double RAM for the image you are processing. Win 10 64 bits Pro edition can handle 512 Gb. The home edition can handle 128 Gb. Of course you need to see if your hardware can handle the memory.
But I think the aproach is wrong
Becouse you need that bitmap as a raw data for a secondary process: convert that to some CAD info.
As we previously saw, the image is going to be dificult to process "per se" in a normal computer. You now need to see if the cad program can interpret that info.
Try to see if you can handle a lower resolution using lets say 4 or 9 blocks of half the linear size or 1/3 the linear size (1/4 or 1/9).
Or if the height info can be stored in some kind of database that can be accesed by delimitated zones. That is how cartography software manage that kind of info.