Is there a way to automatic build a easy wifi fingerprint?

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i want to come true a very easy function that scan wifi and get a position locally;

My origin ideas : keep the wifi location to a database,then query the wifi location from one strong singal wifi.

But the accuacy is very low ,maybe > 200m

so

i want to build a very easy wifi radio-map database on a device with using KNN or other algothrim.

and query the posistion from 4 wifi APS

there is two questions:
1.how to build the radio map automatic locally?
2.how to make the positions from 4 wifis?

thanks