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我们在进行某个时间的降水数据分析的时候，或者指定时间的数据分析，本文我们首先要明确一点就是我们可以设定时间，除了默认的时间外，我们可以选择归一化的时间，也可以选择全球任何一个时区的时间作为时间设定。
iana时区数据库（iana time zone database）是一个全球通用的时区数据库，由互联网号码分配局（iana）维护和发布。该数据库定义了全球范围内的时区信息，包括时区的标识符、名称、偏移量、夏令时规则等。
iana时区数据库被广泛应用于计算机系统中，用于处理日期和时间的转换和计算。它为开发人员和系统管理员提供了一套标准化的时区数据，以便在不同的计算机系统和操作系统中实现一致的时间处理。
使用iana时区数据库，可以根据特定的时区标识符来获取该时区的当前时间、夏令时信息、偏移量等。例如，"america/new_york"表示美国纽约时区，"asia/tokyo"表示日本东京时区。
因为iana时区数据库是一个开放的、全球通用的数据库，所以它可以适用于各种不同的操作系统、编程语言和应用程序。它提供了一个统一的时区标准，帮助各个系统在全球范围内进行时间处理，避免了因为时区差异而导致的时间计算错误。
函数：
ee.date.fromymd(year, month, day, timezone)
returns a date given year, month, day.
arguments:
year (integer)
month (integer)
day (integer)
timezone (string, default: null):
the time zone (e.g. 'america/los_angeles'); defaults to utc.
returns: date
date.fromymd:
[africa/abidjan, africa/accra, africa/addis_ababa, africa/algiers, africa/asmara, africa/asmera, africa/bamako, africa/bangui, africa/banjul, africa/bissau, africa/blantyre, africa/brazzaville, africa/bujumbura, africa/cairo, africa/casablanca, africa/ceuta, africa/conakry, africa/dakar, africa/dar_es_salaam, africa/djibouti, africa/douala, africa/el_aaiun, africa/freetown, africa/gaborone, africa/harare, africa/johannesburg, africa/juba, africa/kampala, africa/khartoum, africa/kigali, africa/kinshasa, africa/lagos, africa/libreville, africa/lome, africa/luanda, africa/lubumbashi, africa/lusaka, africa/malabo, africa/maputo, africa/maseru, africa/mbabane, africa/mogadishu, africa/monrovia, africa/nairobi, africa/ndjamena, africa/niamey, africa/nouakchott, africa/ouagadougou, africa/porto-novo, africa/sao_tome, africa/timbuktu, africa/tripoli, africa/tunis, africa/windhoek, america/adak, america/anchorage, america/anguilla, america/antigua, america/araguaina, america/argentina/buenos_aires, america/argentina/catamarca, america/argentina/comodrivadavia, america/argentina/cordoba, america/argentina/jujuy, america/argentina/la_rioja, america/argentina/mendoza, america/argentina/rio_gallegos, america/argentina/salta, america/argentina/san_juan, america/argentina/san_luis, america/argentina/tucuman, america/argentina/ushuaia, america/aruba, america/asuncion, america/atikokan, america/atka, america/bahia, america/bahia_banderas, america/barbados, america/belem, america/belize, america/blanc-sablon, america/boa_vista, america/bogota, america/boise, america/buenos_aires, america/cambridge_bay, america/campo_grande, america/cancun, america/caracas, america/catamarca, america/cayenne, america/cayman, america/chicago, america/chihuahua, america/ciudad_juarez, america/coral_harbour, america/cordoba, america/costa_rica, america/creston, america/cuiaba, america/curacao, america/danmarkshavn, america/dawson, america/dawson_creek, america/denver, america/detroit, america/dominica, america/edmonton, america/eirunepe, america/el_salvador, america/ensenada, america/fort_nelson, america/fort_wayne, america/fortaleza, america/glace_bay, america/godthab, america/goose_bay, america/grand_turk, america/grenada, america/guadeloupe, america/guatemala, america/guayaquil, america/guyana, america/halifax, america/havana, america/hermosillo, america/indiana/indianapolis, america/indiana/knox, america/indiana/marengo, america/indiana/petersburg, america/indiana/tell_city, america/indiana/vevay, america/indiana/vincennes, america/indiana/winamac, america/indianapolis, america/inuvik, america/iqaluit, america/jamaica, america/jujuy, america/juneau, america/kentucky/louisville, america/kentucky/monticello, america/knox_in, america/kralendijk, america/la_paz, america/lima, america/los_angeles, america/louisville, america/lower_princes, america/maceio, america/managua, america/manaus, america/marigot, america/martinique, america/matamoros, america/mazatlan, america/mendoza, america/menominee, america/merida, america/metlakatla, america/mexico_city, america/miquelon, america/moncton, america/monterrey, america/montevideo, america/montreal, america/montserrat, america/nassau, america/new_york, america/nipigon, america/nome, america/noronha, america/north_dakota/beulah, america/north_dakota/center, america/north_dakota/new_salem, america/nuuk, america/ojinaga, america/panama, america/pangnirtung, america/paramaribo, america/phoenix, america/port-au-prince, america/port_of_spain, america/porto_acre, america/porto_velho, america/puerto_rico, america/punta_arenas, america/rainy_river, america/rankin_inlet, america/recife, america/regina, america/resolute, america/rio_branco, america/rosario, america/santa_isabel, america/santarem, america/santiago, america/santo_domingo, america/sao_paulo, america/scoresbysund, america/shiprock, america/sitka, america/st_barthelemy, america/st_johns, america/st_kitts, america/st_lucia, america/st_thomas, america/st_vincent, america/swift_current, america/tegucigalpa, america/thule, america/thunder_bay, america/tijuana, america/toronto, america/tortola, america/vancouver, america/virgin, america/whitehorse, america/winnipeg, america/yakutat, america/yellowknife, antarctica/casey, antarctica/davis, antarctica/dumontdurville, antarctica/macquarie, antarctica/mawson, antarctica/mcmurdo, antarctica/palmer, antarctica/rothera, antarctica/south_pole, antarctica/syowa, antarctica/troll, antarctica/vostok, arctic/longyearbyen, asia/aden, asia/almaty, asia/amman, asia/anadyr, asia/aqtau, asia/aqtobe, asia/ashgabat, asia/ashkhabad, asia/atyrau, asia/baghdad, asia/bahrain, asia/baku, asia/bangkok, asia/barnaul, asia/beirut, asia/bishkek, asia/brunei, asia/calcutta, asia/chita, asia/choibalsan, asia/chongqing, asia/chungking, asia/colombo, asia/dacca, asia/damascus, asia/dhaka, asia/dili, asia/dubai, asia/dushanbe, asia/famagusta, asia/gaza, asia/harbin, asia/hebron, asia/ho_chi_minh, asia/hong_kong, asia/hovd, asia/irkutsk, asia/istanbul, asia/jakarta, asia/jayapura, asia/jerusalem, asia/kabul, asia/kamchatka, asia/karachi, asia/kashgar, asia/kathmandu, asia/katmandu, asia/khandyga, asia/kolkata, asia/krasnoyarsk, asia/kuala_lumpur, asia/kuching, asia/kuwait, asia/macao, asia/macau, asia/magadan, asia/makassar, asia/manila, asia/muscat, asia/nicosia, asia/novokuznetsk, asia/novosibirsk, asia/omsk, asia/oral, asia/phnom_penh, asia/pontianak, asia/pyongyang, asia/qatar, asia/qostanay, asia/qyzylorda, asia/rangoon, asia/riyadh, asia/saigon, asia/sakhalin, asia/samarkand, asia/seoul, asia/shanghai, asia/singapore, asia/srednekolymsk, asia/taipei, asia/tashkent, asia/tbilisi, asia/tehran, asia/tel_aviv, asia/thimbu, asia/thimphu, asia/tokyo, asia/tomsk, asia/ujung_pandang, asia/ulaanbaatar, asia/ulan_bator, asia/urumqi, asia/ust-nera, asia/vientiane, asia/vladivostok, asia/yakutsk, asia/yangon, asia/yekaterinburg, asia/yerevan, atlantic/azores, atlantic/bermuda, atlantic/canary, atlantic/cape_verde, atlantic/faeroe, atlantic/faroe, atlantic/jan_mayen, atlantic/madeira, atlantic/reykjavik, atlantic/south_georgia, atlantic/st_helena, atlantic/stanley, australia/act, australia/adelaide, australia/brisbane, australia/broken_hill, australia/canberra, australia/currie, australia/darwin, australia/eucla, australia/hobart, australia/lhi, australia/lindeman, australia/lord_howe, australia/melbourne, australia/nsw, australia/north, australia/perth, australia/queensland, australia/south, australia/sydney, australia/tasmania, australia/victoria, australia/west, australia/yancowinna, brazil/acre, brazil/denoronha, brazil/east, brazil/west, cet, cst6cdt, canada/atlantic, canada/central, canada/eastern, canada/mountain, canada/newfoundland, canada/pacific, canada/saskatchewan, canada/yukon, chile/continental, chile/easterisland, cuba, eet, est, est5edt, egypt, eire, etc/gmt, etc/gmt+0, etc/gmt+1, etc/gmt+10, etc/gmt+11, etc/gmt+12, etc/gmt+2, etc/gmt+3, etc/gmt+4, etc/gmt+5, etc/gmt+6, etc/gmt+7, etc/gmt+8, etc/gmt+9, etc/gmt-0, etc/gmt-1, etc/gmt-10, etc/gmt-11, etc/gmt-12, etc/gmt-13, etc/gmt-14, etc/gmt-2, etc/gmt-3, etc/gmt-4, etc/gmt-5, etc/gmt-6, etc/gmt-7, etc/gmt-8, etc/gmt-9, etc/gmt0, etc/greenwich, etc/uct, etc/utc, etc/universal, etc/zulu, europe/amsterdam, europe/andorra, europe/astrakhan, europe/athens, europe/belfast, europe/belgrade, europe/berlin, europe/bratislava, europe/brussels, europe/bucharest, europe/budapest, europe/busingen, europe/chisinau, europe/copenhagen, europe/dublin, europe/gibraltar, europe/guernsey, europe/helsinki, europe/isle_of_man, europe/istanbul, europe/jersey, europe/kaliningrad, europe/kiev, europe/kirov, europe/kyiv, europe/lisbon, europe/ljubljana, europe/london, europe/luxembourg, europe/madrid, europe/malta, europe/mariehamn, europe/minsk, europe/monaco, europe/moscow, europe/nicosia, europe/oslo, europe/paris, europe/podgorica, europe/prague, europe/riga, europe/rome, europe/samara, europe/san_marino, europe/sarajevo, europe/saratov, europe/simferopol, europe/skopje, europe/sofia, europe/stockholm, europe/tallinn, europe/tirane, europe/tiraspol, europe/ulyanovsk, europe/uzhgorod, europe/vaduz, europe/vatican, europe/vienna, europe/vilnius, europe/volgograd, europe/warsaw, europe/zagreb, europe/zaporozhye, europe/zurich, gb, gb-eire, gmt, gmt+0, gmt-0, gmt0, greenwich, hst, hongkong, iceland, indian/antananarivo, indian/chagos, indian/christmas, indian/cocos, indian/comoro, indian/kerguelen, indian/mahe, indian/maldives, indian/mauritius, indian/mayotte, indian/reunion, iran, israel, jamaica, japan, kwajalein, libya, met, mst, mst7mdt, mexico/bajanorte, mexico/bajasur, mexico/general, nz, nz-chat, navajo, prc, pst8pdt, pacific/apia, pacific/auckland, pacific/bougainville, pacific/chatham, pacific/chuuk, pacific/easter, pacific/efate, pacific/enderbury, pacific/fakaofo, pacific/fiji, pacific/funafuti, pacific/galapagos, pacific/gambier, pacific/guadalcanal, pacific/guam, pacific/honolulu, pacific/johnston, pacific/kanton, pacific/kiritimati, pacific/kosrae, pacific/kwajalein, pacific/majuro, pacific/marquesas, pacific/midway, pacific/nauru, pacific/niue, pacific/norfolk, pacific/noumea, pacific/pago_pago, pacific/palau, pacific/pitcairn, pacific/pohnpei, pacific/ponape, pacific/port_moresby, pacific/rarotonga, pacific/saipan, pacific/samoa, pacific/tahiti, pacific/tarawa, pacific/tongatapu, pacific/truk, pacific/wake, pacific/wallis, pacific/yap, poland, portugal, roc, rok, singapore, turkey, uct, us/alaska, us/aleutian, us/arizona, us/central, us/east-indiana, us/eastern, us/hawaii, us/indiana-starke, us/michigan, us/mountain, us/pacific, us/pacific-new, us/samoa, utc, universal, w-su, wet, zulu].
代码
// display gpm precipitation time series
var gpm = ee.imagecollection("nasa/gpm_l3/imerg_v06");
// use iana timezone name
var startdate = ee.date.fromymd(2022, 7, 3,'asia/chongqing')
var enddate = startdate.advance(1, 'day')
// select the calibrated precipitation band
var collection = gpm.select('precipitationcal');
var filtered = collection.filter(ee.filter.date(startdate, enddate))
print(filtered)
// gpm units are mm/hour but image represents 30 mins
// divide by 2 to get the total precipitation within 30 mins
var filtered = filtered.map(function(image) {
return image.divide(2)
.copyproperties(image, ['system:time_start'])
})
var geometry = ee.geometry.point([116.14, 39.95])
// display a time-series chart
var chart = ui.chart.image.series({
imagecollection: filtered,
region: geometry,
reducer: ee.reducer.mean(),
scale: 11132
}).setoptions({
linewidth: 1,
title: 'precipitation time series',
interpolatenulls: true,
vaxis: {title: '30-min precipitation (mm)'}
})
print(chart);
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