2019-10-26 14:33:46 +03:00
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Trumpas įvadas į GIS programuotojui
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===================================
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Jei tau nesvetimos duomenų bazės ar programavimas, ir iš žinių norėjote
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daugiau, šis įrašas -- jums. Labai trumpai susipažinsime, kaip sukurti
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"erdvinę" duomenų bazę ir leisti naudingas užklausas.
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Turinys:
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- Kas yra PostGis?
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- Užduoties aprašymas.
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- Užduoties vykdymas.
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- Pavyzdžiai.
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Kas yra PostGis?
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----------------
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PostGis yra PostgreSQL įskiepis, pridedantis naujų duomenų tipų ir funkcijų,
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skirtų dirbti su erdve. Ką tai reiškia? Išspręskime užduotį ir sužinosime.
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Užduotis
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--------
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Susikurkime PostgreSQL lentelę su viso pasaulio oro uostais (bent tais, kurie
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turi [IATA kodą][1]) ir pažaiskime su duomenimis. Turėdami visus pasaulio oro
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uostus galime sugalvoti daug klausimų, bet man šiuo metu įdomu:
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- kokie du oro uostai yra labiausiai nutolę vienas nuo kito?
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2019-10-26 17:01:07 +03:00
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- kurie du oro uosta yra arčiausiai vienas kito? O toje pačioje šalyje?
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- kokį atstumą skristume aplink žemę, jei iš Vilniaus skristume ta pačia platuma?
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- kiek kartų reikia nuskristi United Economy klase aplink žemę Vilniaus
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platumoje, kad uždirbtume [nemokamus pusryčius][2]?
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2019-10-26 14:33:46 +03:00
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2019-10-26 17:01:07 +03:00
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Duomenų bazės sukūrimas
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-----------------------
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2019-10-26 14:33:46 +03:00
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Susidarys iš kelių dalių:
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- Duomenų bazės sukūrimas.
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- Duomenų importavimas.
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- Užklausos.
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2019-10-26 15:12:18 +03:00
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Oro uostų informaciją gausime iš [openflights.org][3]; `airports.dat` failas
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jūsų patogumui yra šioje repositorijoje. Sukurkime ir importuokime duomenų bazę
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(skriptai paprasti, rekomenduoju peržiūrėti):
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2019-10-26 14:33:46 +03:00
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```
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2019-10-26 15:12:18 +03:00
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$ ./managedb init
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2019-10-26 14:33:46 +03:00
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```
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2019-10-26 17:01:07 +03:00
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Sukūrėme duombazę su visais oro uostais; patikrinkime, kas viduje:
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```
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psql airportgames <<<"
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SELECT
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iata,
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name,
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to_char(st_y (geom), '999.99') AS latitude,
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to_char(st_x (geom), '999.99') AS longitude,
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to_char(st_z (geom), '9999') AS altitude
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FROM
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airports
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WHERE
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iata IN ('VNO', 'RIX', 'TLL');
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"
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iata | name | latitude | longitude | altitude
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------+-------------------------------+----------+-----------+----------
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TLL | Lennart Meri Tallinn Airport | 59.41 | 24.83 | 40
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RIX | Riga International Airport | 56.92 | 23.97 | 11
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VNO | Vilnius International Airport | 54.63 | 25.29 | 198
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```
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Užklausos
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---------
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**Kokie oro uostai yra labiausiai nutolę vienas nuo kito?**
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```
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SELECT
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a.country AS a_country,
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a.name AS a_name,
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a.iata AS a_iata,
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b.country AS b_country,
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b.name AS b_name,
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b.iata AS b_iata,
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to_char(st_distance (a.geom, b.geom, TRUE) / 1000, '99999.99') AS distance_km
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FROM
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airports a,
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airports b
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WHERE
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a.iata != '\N'
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AND b.iata != '\N'
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AND a.gid > b.gid
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2019-10-26 17:01:07 +03:00
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ORDER BY
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distance_km DESC
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LIMIT 10;
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a_country | a_name | a_iata | b_country | b_name | b_iata | distance_km
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------------------+-------------------------------------+--------+-------------------------+------------------------------------+--------+-------------
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China | Zhangjiakou Ningyuan Airport | ZQZ | Argentina | Antoine de Saint Exupéry Airport | OES | 20002.42
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Saudi Arabia | King Khaled Air Base | KMX | French Polynesia | Pukarua Airport | PUK | 20000.78
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Indonesia | Radin Inten II (Branti) Airport | TKG | Colombia | Mariquita Airport | MQU | 20000.53
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French Polynesia | Napuka Island Airport | NAU | Ethiopia | Axum Airport | AXU | 20000.47
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Nicaragua | Corn Island | RNI | Cocos (Keeling) Islands | Cocos (Keeling) Islands Airport | CCK | 20000.20
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China | Jinggangshan Airport | JGS | Argentina | Teniente Benjamin Matienzo Airport | TUC | 19999.93
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Malaysia | Long Lellang Airport | LGL | Brazil | Tefé Airport | TFF | 19998.43
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New Zealand | Hamilton International Airport | HLZ | Spain | Córdoba Airport | ODB | 19998.36
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Indonesia | Sultan Mahmud Badaruddin II Airport | PLM | Colombia | Benito Salas Airport | NVA | 19998.19
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Malaysia | Sultan Ismail Petra Airport | KBR | Peru | Chachapoyas Airport | CHH | 19998.13
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2019-10-26 17:01:07 +03:00
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```
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2019-10-26 17:28:09 +03:00
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**Kurie oro uostai yra arčiausiai vienas kito?**
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2019-10-26 17:18:03 +03:00
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```
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SELECT
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a.country AS a_country,
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a.name AS a_name,
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a.iata AS a_iata,
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b.country AS b_country,
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b.name AS b_name,
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b.iata AS b_iata,
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2019-10-26 17:28:09 +03:00
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to_char(st_distance (a.geom, b.geom, TRUE) / 1000, '99999.99') AS distance_km
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2019-10-26 17:18:03 +03:00
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FROM
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airports a,
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airports b
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WHERE
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a.iata != '\N'
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AND b.iata != '\N'
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AND a.gid > b.gid
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ORDER BY
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distance_km ASC
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LIMIT 10;
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2019-10-26 17:28:09 +03:00
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a_country | a_name | a_iata | b_country | b_name | b_iata | distance_km
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------------------+---------------------------------------+--------+------------------+-----------------------------------------------------+--------+-------------
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Australia | Shute Harbour Airport | JHQ | Australia | Whitsunday Island Airport | WSY | 0.14
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Papua New Guinea | Nadunumu Airport | NDN | Papua New Guinea | Kagi Airport | KGW | 1.83
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Papua New Guinea | Kagi Airport | KGW | Papua New Guinea | Efogi Airport | EFG | 2.24
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Rwanda | Gisenyi Airport | GYI | Congo (Kinshasa) | Goma International Airport | GOM | 2.38
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United Kingdom | Westray Airport | WRY | United Kingdom | Papa Westray Airport | PPW | 2.83
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Papua New Guinea | Nadunumu Airport | NDN | Papua New Guinea | Efogi Airport | EFG | 2.92
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Papua New Guinea | Bodinumu Airport | BNM | Papua New Guinea | Kagi Airport | KGW | 3.13
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Virgin Islands | Charlotte Amalie Harbor Seaplane Base | SPB | Virgin Islands | Cyril E. King Airport | STT | 3.46
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United States | Brown Field Municipal Airport | SDM | Mexico | General Abelardo L. Rodríguez International Airport | TIJ | 3.59
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French Guiana | Saint-Laurent-du-Maroni Airport | LDX | Suriname | Albina Airport | ABN | 3.71
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2019-10-26 17:18:03 +03:00
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```
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2019-10-26 17:01:07 +03:00
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**Kokį atstumą skristume aplink žemę, jei iš Vilniaus skristume ta pačia platuma?**
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**Kiek kartų reikia nuskristi United Economy klase aplink žemę Vilniaus
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platumoje, kad uždirbtume [nemokamus pusryčius][2]?**
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2019-10-26 14:33:46 +03:00
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[1]: https://en.wikipedia.org/wiki/International_Air_Transport_Association_code
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[2]: https://www.united.com/ual/en/us/fly/mileageplus/premier/full-premier-benefits-chart.html
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[3]: https://openflights.org/data.html
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