Inaccuracy in the GPS data
Can I obtain these inaccuracy from the GPS chip datasheet?


No, because that's not a static thing  – it depends on how many satellites your receiver receives at the moment, how strong the signals are, how long the receiver has been observing, at which temperature the receiver is operating, your speed, at which angles the satellites are, at which rate temperature is changing, your height, the availability of secondary info (like AGPS data), component aging...

Many GPS transmitters do emit standard format GPS messages, and these can (but not necessarily do, although it is a common feature) a positional variance estimate, which you can directly extract from these messages. Consult your GPS chipset's datasheet and any NMEA reference, if that's the format your GPS gives you.