![\"Zurich](\"http:\/\/www.ralphstraumann.ch\/blog\/wp-content\/uploads\/2013\/06\/zurich_sky.png\" "\\"Zurich")
<\/a>The SWITCH archive features one image every hour. Luckily for my project, the URLs of the individual pictures adhere to a nice structured format which makes automatic downloading of several thousand images rather easy. An example is here:<\/span><\/p>\n So, the URL encodes year, month and day (each twice) and the hour. I have written a Python script that iterates through all hours of every year between 2008 and 2012 and downloads the respective image. A standard year (non-leap year) has\u00a08,760 of them.<\/p>\n I also wrote a second Python script that checks for data gaps. There have been some few hours for which my script didn’t get an image. I didn’t investigate this further (whether it was my internet connection, a hickup of Python\/urllib2 or the Switch server or archive), but filled the gaps with the respective hour of an adjacent day. I did the same with the gap that is created by the change from normal time to daylight-saving time in spring (advancing the clock by one hour).<\/p>\n I then drew a binary (black-white) mask of the sky in the webcam picture.\u00a0For the next processing step I shrunk all pictures to a smaller format, since otherwise processing time would have been very long. Iterating over all pictures of a year, I used the Python Image Library (PIL) to extract the average colour of the sky (employing a na\u00efve approach of averaging the R,G,B values in the masked area) and record it in a file. The files of the years 2008 to 2012 have then been used to draw the Zurich Sky<\/em>.<\/p>\n I first employed a fully browser- and vector-based approach which loaded the colour values from afore-mentioned files. It worked well in Chrome but was painfully slow in Internet Explorer. Thus I changed the representation to raster images. As a gimmick I also included a picture that aggregates (overlays) all years 2008\u20132012 into one. Using some HTML\/JS\/Jquery magic I can also access the mouse coordinates when you hover over the image and compute the date and time and display it above the image.<\/p>\n Now, enjoy\u00a0Zurich Sky<\/a><\/em><\/strong>, and let me know what you think.<\/p>\n I will follow up on this by a second post that looks at some of the interesting features that can be seen in Zurich Sky<\/em>. Please share your discoveries in the comments below!<\/p>\n <\/p>\n","protected":false},"excerpt":{"rendered":" … is the title of my most recent project. It’s a bit artsy, but I think some of the concepts behind it may also have practical applications in this world of ever more abundant webcam footage (maybe need to think a bit more on this point later). In Zurich Sky, I destilled yearly aggregates of … Continue reading Zurich Sky<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":1301,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[8],"tags":[17,51,52,64,125,140],"class_list":["post-1299","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-piece","tag-art","tag-fun","tag-geo","tag-imagery","tag-visualization","tag-web-scraping"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"https:\/\/www.ralphstraumann.ch\/blog\/wp-content\/uploads\/2013\/06\/zurich_sky.png","jetpack_shortlink":"https:\/\/wp.me\/p3pPwF-kX","jetpack_sharing_enabled":true,"jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/www.ralphstraumann.ch\/blog\/wp-json\/wp\/v2\/posts\/1299","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ralphstraumann.ch\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ralphstraumann.ch\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ralphstraumann.ch\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ralphstraumann.ch\/blog\/wp-json\/wp\/v2\/comments?post=1299"}],"version-history":[{"count":14,"href":"https:\/\/www.ralphstraumann.ch\/blog\/wp-json\/wp\/v2\/posts\/1299\/revisions"}],"predecessor-version":[{"id":1424,"href":"https:\/\/www.ralphstraumann.ch\/blog\/wp-json\/wp\/v2\/posts\/1299\/revisions\/1424"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.ralphstraumann.ch\/blog\/wp-json\/wp\/v2\/media\/1301"}],"wp:attachment":[{"href":"https:\/\/www.ralphstraumann.ch\/blog\/wp-json\/wp\/v2\/media?parent=1299"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ralphstraumann.ch\/blog\/wp-json\/wp\/v2\/categories?post=1299"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ralphstraumann.ch\/blog\/wp-json\/wp\/v2\/tags?post=1299"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}http:\/\/cam.switch.ch\/pano\/2013\/0621\/zueri_n201306211300.jpg<\/a><\/code>
\n![\"\"](\"http:\/\/cam.switch.ch\/pano\/2013\/0621\/zueri_n201306211300.jpg\")
(as can be seen from\u00a0this webpage<\/a>)<\/p>\n