前言
最近，我使用爬虫技术，爬取了美国航空航天局，也就是你电影里经常见到的 NASA, 火星探索的相关图片，有 10000 张吧。
嗯嗯，小事情，小事情。
完事儿之后，有点小激动，于是就有了这篇文章，将有以下内容：
我为什么要爬NASA的图片
我已经超过35了，瑟瑟发抖啥时候被开了。
天天想着万一哪天失业了干点啥，想着玩个自媒体吧，天天给大家瞎白话。白话点历史谜团，宇宙奥秘啥的，于是我就盯上了 NASA。
NASA 有各种宇宙探索任务，并且有相关的文章，访谈，图片，视频公开，这是不可多得的资源库。
我是如何爬取NASA图片的（超详细）
NASA 的网站是可以公开访问的，地址是
https://www.nasa.gov/
打开以后，它首页长这样，可以看到各种内容。右上角还有个搜索框，我们输入 Mars 也就是 火星
稍等片刻，会展示出与 Mars 相关的各种内容，其中有一项 Mars Exploration 也就是 火星探索
点开之后，就到了一个新页面，然后找到 Images 图片，就到了我们爬取的目标页
https://www.nasa.gov/mission_pages/mars/images/index.html
页面下拉，你将会看到有个大大的按钮，上面写着 MORE IMAGES， 点击试试你就发现：
页面的内容，并不是页面直接加载的，而是通过 api 请求后，异步渲染的
F12, 打开浏览器开发者模式,重新执行刚才的步骤，观察请求信息，发现都会有如下的情况
看上去这个url地址非常重要，我们先看他的请求地址：
https://www.nasa.gov/api/2/ubernode/_search?size=24&from=24&sort=promo-date-time%3Adesc&q=((ubernode-type%3Aimage)%20AND%20(topics%3A3152))&_source_include=promo-date-time%2Cmaster-image%2Cnid%2Ctitle%2Ctopics%2Cmissions%2Ccollections%2Cother-tags%2Cubernode-type%2Cprimary-tag%2Csecondary-tag%2Ccardfeed-title%2Ctype%2Ccollection-asset-link%2Clink-or-attachment%2Cpr-leader-sentence%2Cimage-feature-caption%2Cattachments%2Curi
注意看里面的参数
size=24&from=24
很显然，size 就是每次请求图片的数量，from 经过试验，是查询初始位置，我们可以改它来获取其他内容
我们再来看看它的返回信息：
{
"took": 3,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"skipped": 0,
"failed": 0
},
"hits": {
"total": 659,
"max_score": null,
"hits": [{
"_index": "nasa-public",
"_type": "ubernode",
"_id": "450040",
"_score": null,
"_source": {
"image-feature-caption": "Mars 2020 rover underwent an eye exam after several cameras were installed on the rover. ",
"topics": ["3140", "3152"],
"nid": "450040",
"title": "NASA 'Optometrists' Verify Mars 2020 Rover's 20/20 Vision",
"type": "ubernode",
"uri": "/image-feature/jpl/nasa-optometrists-verify-mars-2020-rovers-2020-vision",
"collections": ["4525", "5246"],
"link-or-attachment": "link",
"missions": ["6336"],
"primary-tag": "6336",
"cardfeed-title": "NASA 'Optometrists' Verify Mars 2020 Rover's 20/20 Vision",
"promo-date-time": "2019-08-05T17:49:00-04:00",
"secondary-tag": "3140",
"master-image": {
"fid": "603128",
"alt": "Engineers test cameras on the top of the Mars 2020 rover’s mast and front chassis. ",
"width": "1600",
"id": "603128",
"title": "Engineers test cameras on the top of the Mars 2020 rover’s mast and front chassis. ",
"uri": "public://thumbnails/image/pia23314-16.jpg",
"height": "900"
},
"ubernode-type": "image"
},
"sort": [1565041740000]
}, {
"_index": "nasa-public",
"_type": "ubernode",
"_id": "433172",
"_score": null,
"_source": {
"image-feature-caption": "NASA still hasn't heard from the Opportunity rover, but at least we can see it again.",
"topics": ["3152"],
"nid": "433172",
"title": "Opportunity Emerges in a Dusty Picture",
"type": "ubernode",
"uri": "/image-feature/opportunity-emerges-in-a-dusty-picture",
"collections": ["7628"],
"link-or-attachment": "link",
"missions": ["3639"],
"primary-tag": "3152",
"cardfeed-title": "Opportunity Emerges in a Dusty Picture",
"promo-date-time": "2018-09-26T12:39:00-04:00",
"secondary-tag": "7628",
"master-image": {
"fid": "584263",
"alt": "NASA's Opportunity rover appears as a blip in the center of this square",
"width": "1400",
"id": "584263",
"title": "NASA's Opportunity rover appears as a blip in the center of this square",
"uri": "public://thumbnails/image/pia22549-16.jpg",
"height": "788"
},
"ubernode-type": "image"
},
"sort": [1537979940000]
}]
}
}
上面的 json 内容太长，我删除了一些重复的，实际上 hits 这个数组，也是24个，和页面上显示的图片数量是一样的。那基本可以断定，页面上的信息，就是从这个数组来的。
进而对比发现，master-image字段下，就是我们需要的信息，包括 图片地址, 图片尺寸, 图片标题。
下面就上代码，组装请求URL, 获取内容，下载图片 三步走
我使用了 Dart 语言，你们随意
import 'dart:convert';
import 'package:dio/dio.dart';
main() async {
// 每页数量是固定24个,改变初始值即可
for (int from = 0; from < 24 * 100; from = from + 24) {
await getPage(from);
}
}
//获取每一页的信息并且下载
Future<void> getPage(int from) async {
String url = 'https://www.nasa.gov/api/2/ubernode/_search?size=24&from=' +
from.toString() +
'&sort=promo-date-time%3Adesc&q=((ubernode-type%3Aimage)%20AND%20(topics%3A3152))&_source_include=promo-date-time%2Cmaster-image%2Cnid%2Ctitle%2Ctopics%2Cmissions%2Ccollections%2Cother-tags%2Cubernode-type%2Cprimary-tag%2Csecondary-tag%2Ccardfeed-title%2Ctype%2Ccollection-asset-link%2Clink-or-attachment%2Cpr-leader-sentence%2Cimage-feature-caption%2Cattachments%2Curi';
//获取到内容
var res = await Dio().get(url);
var map = jsonDecode(res.toString());
(map['hits']['hits'] as List<dynamic>).forEach((element) async {
Uri fileUri = Uri.parse(getUri(element));
String savePath = getSavePath(element);
await Dio().downloadUri(fileUri, savePath);
print('已下载: ' + savePath);
});
}
//获取图片下载地址
String getUri(dynamic element) {
String uri = element['_source']['master-image']['uri'].toString();
uri = uri.replaceAll('public://',
'https://www.nasa.gov/sites/default/files/styles/full_width_feature/public/');
return uri;
}
//处理信息，并且返回图片保存地址
String getSavePath(dynamic element) {
String id = element['_id'];
String fid = element['_source']['master-image']['fid'].toString();
String title = element['_source']['master-image']['title'].toString();
String uri = element['_source']['master-image']['uri'].toString();
String savePath =
id + '_' + fid + '_' + title.trim() + '.' + uri.split('.').last;
savePath = savePath.replaceAll('/', '');
savePath = savePath.replaceAll('\\', '');
savePath = savePath.replaceAll('"', '');
savePath = 'images/' + savePath;
return savePath;
}
上面的代码，还是很简单的，有经验的同学应该一看就懂。
走起来吧。
已下载: images/470436_643588_This is the third color image taken by NASA’s Ingenuity helicopter.jpg
已下载: images/470435_643587_This is the second color image taken by NASA’s Ingenuity helicopter.jpg
已下载: images/468546_639327_This is the first high-resolution, color image to be sent back by the Hazard Cameras (Hazcams).jpg
已下载: images/452007_605784_Danielson Crater on Mars.jpg
已下载: images/458478_615132_Gullies on Mars.jpg
已下载: images/469416_641582_A field of sand dunes occupies this frosty 5-kilometer diameter crater in the high-latitudes of the northern plains of Mars..jpeg
已下载: images/458075_614251_Mars 2020 With Sample Tubes (Artist's Concept).jpg
已下载: images/470381_643473_CME.jpg
已下载: images/458813_615896_Mars.jpg
已下载: images/467026_635309_Illustration of NASA’s Perseverance rover begins its descent through the Martian atmosphere.jpg
已下载: images/470438_643591_This black and white image was taken by NASA’s Ingenuity helicopter during its third flight on April 25, 2021.jpg
已下载: images/465488_631398_Cliffs in Ancient Ice on Mars.jpg
已下载: images/463659_626874_Avalanche on Mars.jpg
已下载: images/470251_643164_This image from NASA’s Perseverance rover shows the agency’s Ingenuity Mars Helicopter right after it successfully completed a high-speed spin-up test..jpeg
已下载: images/468636_639726_Mars' Jezero Crater.jpg
我得到了什么
这些图片
还有这些
图片，图片标题都有了, 够看一个月了我估计。
我发现了什么秘密
这张图，我最喜欢了。一个如此清晰，一个如此浑浊，这是为什么？ 火星人的裂缝产生器？
好吧，真正的秘密是：
NASA 的网站竟然没有防采集，不信你也试试。。。
