Previous Halacha:: 
If the bathroom in the park is its own structure, such as a mobile bathroom, or a building that is designated only as a bathroom, then one may not learn or pray within its four cubits [i.e. two meters]. Likewise one may not learn or pray if the bathroom is within one’s view, even if he is further than four cubits. One is to thus turn his back to the bathroom walls to be allowed to pray and learn.
May one pray or learn in a house/Shul if he can see a mobile bathroom from his open door/window?
This matter is disputed in Poskim. Practically, although the main ruling follows the lenient opinion, nevertheless it is best to be stringent that the bathroom not to be within one’s sight. [This stringency however is only required if the window or door is open, as according to all opinions there is no issue in seeing the mobile bathroom through a closed transparent window or door.] Likewise, according to all it suffices to close one’s eyes when inside the house even if one is facing it, and at night, if one cannot see the bathroom due to lack of light, it is permitted to pray or learn in ones house even if one is facing it through an open window or door.
 Based on previous Halacha-see there
 Admur 79/5 and Michaber 79/2 regaridng having feces in the next room and according to Admur the same applies in this case of mobile bathrooms outside one’s home, being that a mobile bathroom is viewed as feces according to Admur ibid.
 Regarding a person being in a different room than the feces, Admur ibid rules as follows: If a person is in one room reading the Shema and the feces are in another room, then even if the door is opened between the two rooms and he is sitting by the opening which is near the feces, nevertheless it is permitted to read the Shema in that area so long as he does not smell the feces. The reason for this is because the opening of the room is considered as if it is closed, being that it contains doorposts [Lit. Gifufim] that separate it from the room that contains the feces. [1st opinion in Admur ibid and Michaber ibid; Rosh Brachos 3/46] However there is an opinion [Rashba Brachos 25a; 2nd opinion in Admur and Michaber ibid] that rules it is forbidden to read the Shema while the feces is within one’s view, even when it is in a different domain. Practically, the main ruling follows the former opinion, as since the feces is in another room it is not relevant whether he can see it, as it is considered like feces in a glass container of which all agree that there is no prohibition in seeing it. [Thus, the feces may be within 4 amos of the person outside the room and the door may be open with the visible feces.] Nevertheless, it is proper to suspect for the latter opinion [and not have the feces within one’s sight]. [Admur ibid; Beis Yosef; Ateres Zekeinim 79/2]
 As this is similar to feces that are in a glass container of which all agree do not contain a prohibition.
 Admur ibid; M”A 79/8
The reason: As since he is in a different domain and does not physically see it, all agree it is eprmiktted. [ibid]