alex-hhh/example0.rkt

## example0.rkt
#lang racket
(require json)

;; Example 0: Load and manipulate the Timezone GeoJSON file

;; You will also need to download timezone data from:
;;
;; https://github.com/evansiroky/timezone-boundary-builder/releases

;; Copyright (c) 2019 Alex Harsányi

;; Permission is hereby granted, free of charge, to any person obtaining a
;; copy of this software and associated documentation files (the "Software"),
;; to deal in the Software without restriction, including without limitation
;; the rights to use, copy, modify, merge, publish, distribute, sublicense,
;; and/or sell copies of the Software, and to permit persons to whom the
;; Software is furnished to do so, subject to the following conditions:

;; The above copyright notice and this permission notice shall be included in
;; all copies or substantial portions of the Software.

;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
;; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
;; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
;; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
;; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
;; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
;; DEALINGS IN THE SOFTWARE.


(define timezone-data (time (call-with-input-file "./combined.json" read-json)))

;; Extract a random sample from a json OBJECT -- this can be used on the
;; timezone-data to obtain a smaller object which can be printed and inspected
;; while developing the functions which manipulate the actual timezone data...
(define (random-sample object [max-size 5])
  (cond
    ((hash? object)
     ;; for hash tables, copy all the keys, but simplify the values
     (for/hash ([(k v) (in-hash object)])
       (values k (random-sample v max-size))))
    ((list? object)
     ;; Short lists are copied directly, but we only sample MAX-SIZE random
     ;; values from longer lists.  In both cases the values themselves are
     ;; further simplified.
     (let ([len (length object)])
       (if (> len max-size)
           (let ([samples (sort (build-list max-size (lambda (x) (random len))) <)])
             (for/list ([(x position) (in-indexed (in-list object))]
                        #:when (member position samples))
               (random-sample x max-size)))
           (for/list ([x (in-list object)])
             (random-sample x max-size)))))
    (#t
     ;; Any other objects are not simplified.
     object)))

;; Every GeoJSON node will have type and properties keys
(define (geojson-type node)
  (hash-ref node 'type #f))
(define (geojson-properties node)
  (hash-ref node 'properties (lambda () (hash))))

(define (geojson-features node)
  (let ([type (geojson-type node)])
    (if (equal? type "FeatureCollection")
        (hash-ref node 'features null)
        (error (format "geojson-features: bad node type: ~a" type)))))

(define (geojson-geometry node)
  (let ([type (geojson-type node)])
    (if (equal? type "Feature")
        (hash-ref node 'geometry (lambda () (hash)))
        (error (format "geojson-geometry: bad node type: ~a" type)))))

(define (geojson-coordinates node)
  (let ([type (geojson-type node)])
    (if (member type '("Point" "LineString" "Polygon" "MultiPoint" "MultiLineString" "MultiPolygon"))
        (hash-ref node 'coordinates null)
        (error (format "geojson-coordinates: bad node type: ~a" type)))))

;; Count the number of points in a geometry GeoJSON node
(define (geojson-geometry-point-count node)
  (let ([type (geojson-type node)]
        [coordinates (geojson-coordinates node)])
    (cond ((equal? type "Point")
           ;; Coordinates is a single point
           1)
          ((equal? type "LineString")
           ;; List of points
           (length coordinates))
          ((equal? type "Polygon")
           ;; List of lists of points (main and holes.  Count them all
           (for/fold ([result 0])
                     ([line (in-list coordinates)])
             (+ result (length line))))
          ((equal? type "MultiPoint")
           ;; List of points
           (length coordinates))
          ((equal? type "MultiLineString")
           (for/fold ([result 0])
                     ([line (in-list coordinates)])
             (+ result (length line))))
          ((equal? type "MultiPolygon")
           (for/fold ([result 0])
                     ([polygon (in-list coordinates)])
             (+ result
                (for/fold ([result 0])
                          ([line (in-list polygon)])
                  (+ result (length line))))))
          (#t
           (error (format "Unknown geometry type: ~a" type))))))

;; Count the number of points in a GeoJSON node and its sub-nodes.
(define (geojson-point-count node)
  (let ((type (geojson-type node)))
    (cond ((equal? type "FeatureCollection")
           (for/fold ([result 0])
                     ([feature (in-list (geojson-features node))])
             (+ result (geojson-point-count feature))))
          ((equal? type "Feature")
           (let ((geometry (geojson-geometry node)))
             (geojson-geometry-point-count geometry))))))

;; return the timezone name stored in a GeoJSON feature
(define (tz-name node)
  (let ((properties (geojson-properties node)))
    (hash-ref properties 'tzid #f)))

;; Print a summary of the point count in the timezone data JSON
(define (analyze-tz-point-count node)
  (define nzones (length (geojson-features node)))
  (define total (geojson-point-count node))
  (define tz-point-count
    (for/list ([feature (in-list (geojson-features node))])
      (list (tz-name feature) (geojson-point-count feature))))
  (set! tz-point-count
        (sort tz-point-count
              (lambda (a b)
                (match-define (list _ p1) a)
                (match-define (list _ p2) b)
                (> p1 p2))))
  (printf "Total point count: ~a, total zone count ~a~%" total nzones)
  (for ([tp (in-list tz-point-count)])
    (match-define (list name pcount) tp)
    (printf "~a ~a~%" name pcount)))

## example1.rkt
#lang racket
(require racket/draw)
(define dc (new bitmap-dc% [bitmap (make-object bitmap% 250 250)]))
(send* dc
  (set-pen (send the-pen-list find-or-create-pen "black" 5.0 'solid))
  (set-brush (send the-brush-list find-or-create-brush "red" 'solid))
  (draw-rectangle 10 10 (- 250 20) (- 250 20)))
(define bm (send dc get-bitmap))
(send bm save-file "example1.png" 'png)

## example2.rkt
#lang racket
(require racket/draw)
(define dc (new bitmap-dc% [bitmap (make-object bitmap% 250 250)]))
(send* dc
  (set-scale 250/2 250/2)
  (set-origin 250/2 250/2)
  (set-pen (send the-pen-list find-or-create-pen "black" 0.00001 'solid))
  (set-brush (send the-brush-list find-or-create-brush "black" 'transparent))
  (draw-rectangle -1 -1 2 2)
  (set-brush (send the-brush-list find-or-create-brush "red" 'solid))
  (draw-line -1 0 1 0)
  (draw-line 0 -1 0 1))
(define bm (send dc get-bitmap))
(send bm save-file "example2.png" 'png)

## example3.rkt
#lang racket
(require racket/draw)

(define path (new dc-path%))
(send path move-to 1 0)
(for ([p (in-range 0 (* 2 pi) (/ (* 2 pi) 5))])
  (define x (cos p))
  (define y (sin p))
  (send path line-to x y))
(send path close)

(define dc (new bitmap-dc% [bitmap (make-object bitmap% 250 250)]))
(send* dc
  (set-smoothing 'smoothed)
  (set-scale 250/2 250/2)
  (set-origin 250/2 250/2)
  (set-pen (send the-pen-list find-or-create-pen "black" 0.01 'solid))
  (set-brush (send the-brush-list find-or-create-brush "red" 'solid))
  (draw-path path))
(define bm (send dc get-bitmap))
(send bm save-file "example3.png" 'png)

## example4.rkt
#lang racket

;; Example 4: Render the timezone data using a small color map

;; You will also need to download timezone data from:
;;
;; https://github.com/evansiroky/timezone-boundary-builder/releases

;; Copyright (c) 2019 Alex Harsányi

;; Permission is hereby granted, free of charge, to any person obtaining a
;; copy of this software and associated documentation files (the "Software"),
;; to deal in the Software without restriction, including without limitation
;; the rights to use, copy, modify, merge, publish, distribute, sublicense,
;; and/or sell copies of the Software, and to permit persons to whom the
;; Software is furnished to do so, subject to the following conditions:

;; The above copyright notice and this permission notice shall be included in
;; all copies or substantial portions of the Software.

;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
;; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
;; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
;; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
;; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
;; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
;; DEALINGS IN THE SOFTWARE.


(require json racket/draw math/base)

(define (lat-lon->map-point coordinates)
  (match-define (list lon lat _ ...) coordinates)
  (define-values (x y) (values (degrees->radians lon) (asinh (tan (degrees->radians lat)))))
  (list (/ (+ 1 (/ x pi)) 2) (/ (- 1 (/ y pi)) 2)))

(define (draw-polygon dc polygons)
  (define path
    (for/fold ([path #f]) ([polygon (in-list polygons)] #:unless (null? polygon))
      (define sub-path (new dc-path%))
      (send/apply sub-path move-to (lat-lon->map-point (car polygon)))
      (for ([point (in-list (cdr polygon))])
        (send/apply sub-path line-to (lat-lon->map-point point)))
      (send sub-path close)
      (if path (begin (send path append sub-path) path) sub-path)))
  (and path (send dc draw-path path 0 0)))

(define (draw-feature dc feature)
  (let* ([geometry (hash-ref feature 'geometry (lambda () (hash)))]
         [data (hash-ref geometry 'coordinates (lambda () null))])
    (case (hash-ref geometry 'type #f)
      (("Polygon") (draw-polygon dc data))
      (("MultiPolygon") (for ([polygon (in-list data)]) (draw-polygon dc polygon)))
      (else (printf "Skipping ~a geometry" (hash-ref geometry 'type #f))))))

(define color-map
  (list (make-object color% 78 121 165)
        (make-object color% 241 143 59)
        (make-object color% 224 88 91)
        (make-object color% 119 183 178)
        (make-object color% 90 161 85)
        (make-object color% 237 201 88)
        (make-object color% 175 122 160)
        (make-object color% 254 158 168)
        (make-object color% 156 117 97)
        (make-object color% 186 176 172)))

(define (make-timezone-bitmap tzdata width height)
  (define dc (new bitmap-dc% [bitmap (make-object bitmap% width height)]))
  (send* dc
    (set-scale width height)
    (set-smoothing 'smoothed)
    (set-pen (send the-pen-list find-or-create-pen "black" (* 0.5 (/ 1 width)) 'solid)))
  ;; Iterate over each feature (timezone) and render it
  (for ([feature  (in-list (hash-ref tzdata 'features))]
        [color (in-cycle (in-list color-map))])
    (send dc set-brush (send the-brush-list find-or-create-brush color 'solid))
    (draw-feature dc feature))
  (send dc get-bitmap))

(define timezone-data (time (call-with-input-file "./combined.json" read-json)))
(define bm (make-timezone-bitmap timezone-data 800 700))
(send bm save-file "timezone-map.png" 'png 100 #:unscaled? #t)

## example5.rkt
#lang racket
(require json racket/draw math/base)

;; Example 5: Render the timezone data using a a unique color for each color
;; map

;; You will also need to download timezone data from:
;;
;; https://github.com/evansiroky/timezone-boundary-builder/releases

;; Copyright (c) 2019 Alex Harsányi

;; Permission is hereby granted, free of charge, to any person obtaining a
;; copy of this software and associated documentation files (the "Software"),
;; to deal in the Software without restriction, including without limitation
;; the rights to use, copy, modify, merge, publish, distribute, sublicense,
;; and/or sell copies of the Software, and to permit persons to whom the
;; Software is furnished to do so, subject to the following conditions:

;; The above copyright notice and this permission notice shall be included in
;; all copies or substantial portions of the Software.

;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
;; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
;; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
;; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
;; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
;; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
;; DEALINGS IN THE SOFTWARE.


(define (lat-lon->map-point coordinates)
  (match-define (list lon lat _ ...) coordinates)
  (define-values (x y) (values (degrees->radians lon) (asinh (tan (degrees->radians lat)))))
  (list (/ (+ 1 (/ x pi)) 2) (/ (- 1 (/ y pi)) 2)))

(define (draw-polygon dc polygons)
  (define path
    (for/fold ([path #f]) ([polygon (in-list polygons)] #:unless (null? polygon))
      (define sub-path (new dc-path%))
      (send/apply sub-path move-to (lat-lon->map-point (car polygon)))
      (for ([point (in-list (cdr polygon))])
        (send/apply sub-path line-to (lat-lon->map-point point)))
      (send sub-path close)
      (if path (begin (send path append sub-path) path) sub-path)))
  (and path (send dc draw-path path 0 0)))

(define (draw-feature dc feature)
  (let* ([geometry (hash-ref feature 'geometry (lambda () (hash)))]
         [data (hash-ref geometry 'coordinates (lambda () null))])
    (case (hash-ref geometry 'type #f)
      (("Polygon") (draw-polygon dc data))
      (("MultiPolygon") (for ([polygon (in-list data)]) (draw-polygon dc polygon)))
      (else (printf "Skipping ~a geometry" (hash-ref geometry 'type #f))))))

(define (tz-name node)
  (let ((properties (hash-ref node 'properties)))
    (hash-ref properties 'tzid #f)))

(define (allocate-color id)
  (let* ((b (exact-floor (/ id 100)))
         (g (exact-floor (/ (- id (* b 100)) 10)))
         (r (exact-floor (- id (* b 100) (* g 10)))))
    (make-object color% (* r 28) (* g 28) (* b 28))))

(struct tzdata (name id color) #:transparent)

(define (allocate-tzdata node)
  (define next-id 1)  ; start at 1, 0 is reserved for "no tz data", the oceans
  (for/list ([tznode (in-list (hash-ref node 'features))])
    (define name (tz-name tznode))
    (define id next-id)
    (set! next-id (add1 next-id))
    (define color (allocate-color id))
    (tzdata name id color)))

(define (time-zone-color tz-data name)
  (for/first ([t (in-list tz-data)] #:when (equal? (tzdata-name t) name))
    (tzdata-color t)))

(define color-map
  (list (make-object color% 78 121 165)
        (make-object color% 241 143 59)
        (make-object color% 224 88 91)
        (make-object color% 119 183 178)
        (make-object color% 90 161 85)
        (make-object color% 237 201 88)
        (make-object color% 175 122 160)
        (make-object color% 254 158 168)
        (make-object color% 156 117 97)
        (make-object color% 186 176 172)))

(define (make-timezone-bitmap tzdata width height)
  (define tz-data (allocate-tzdata timezone-data))
  (define dc (new bitmap-dc% [bitmap (make-object bitmap% width height)]))
  (send* dc
    (set-scale width height)
    (set-smoothing 'smoothed)
    (set-pen (send the-pen-list find-or-create-pen "black" (* 0.5 (/ 1 width)) 'solid)))
  ;; Iterate over each feature (timezone) and render it
  (for ([feature  (in-list (hash-ref tzdata 'features))])
    (define color (time-zone-color tz-data (tz-name feature)))
    (send dc set-brush (send the-brush-list find-or-create-brush color 'solid))
    (draw-feature dc feature))
  (send dc get-bitmap))

(define timezone-data (call-with-input-file "./combined.json" read-json))
(define bm (make-timezone-bitmap timezone-data 800 500))
(send bm save-file "timezone-map-2.png" 'png 100 #:unscaled? #t)

## example6.rkt
#lang racket
(require json racket/draw math/base)

;; Example 6: Render a subset of the map

;; You will also need to download timezone data from:
;;
;; https://github.com/evansiroky/timezone-boundary-builder/releases

;; Copyright (c) 2019 Alex Harsányi

;; Permission is hereby granted, free of charge, to any person obtaining a
;; copy of this software and associated documentation files (the "Software"),
;; to deal in the Software without restriction, including without limitation
;; the rights to use, copy, modify, merge, publish, distribute, sublicense,
;; and/or sell copies of the Software, and to permit persons to whom the
;; Software is furnished to do so, subject to the following conditions:

;; The above copyright notice and this permission notice shall be included in
;; all copies or substantial portions of the Software.

;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
;; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
;; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
;; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
;; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
;; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
;; DEALINGS IN THE SOFTWARE.

(define (lat-lon->map-point coordinates)
  (match-define (list lon lat _ ...) coordinates)
  (define-values (x y) (values (degrees->radians lon) (asinh (tan (degrees->radians lat)))))
  (list (/ (+ 1 (/ x pi)) 2) (/ (- 1 (/ y pi)) 2)))

(define (draw-polygon dc polygons)
  (define path
    (for/fold ([path #f]) ([polygon (in-list polygons)] #:unless (null? polygon))
      (define sub-path (new dc-path%))
      (send/apply sub-path move-to (lat-lon->map-point (car polygon)))
      (for ([point (in-list (cdr polygon))])
        (send/apply sub-path line-to (lat-lon->map-point point)))
      (send sub-path close)
      (if path (begin (send path append sub-path) path) sub-path)))
  (and path (send dc draw-path path 0 0)))

(define (draw-feature dc feature)
  (let* ([geometry (hash-ref feature 'geometry (lambda () (hash)))]
         [data (hash-ref geometry 'coordinates (lambda () null))])
    (case (hash-ref geometry 'type #f)
      (("Polygon") (draw-polygon dc data))
      (("MultiPolygon") (for ([polygon (in-list data)]) (draw-polygon dc polygon)))
      (else (printf "Skipping ~a geometry" (hash-ref geometry 'type #f))))))

(define (tz-name node)
  (let ((properties (hash-ref node 'properties)))
    (hash-ref properties 'tzid #f)))

(define color-map
  (list (make-object color% 78 121 165)
        (make-object color% 241 143 59)
        (make-object color% 224 88 91)
        (make-object color% 119 183 178)
        (make-object color% 90 161 85)
        (make-object color% 237 201 88)
        (make-object color% 175 122 160)
        (make-object color% 254 158 168)
        (make-object color% 156 117 97)
        (make-object color% 186 176 172)))

(define (setup-dc dc min-coord max-coord)
  (define-values (width height) (send dc get-size))
  (match-define (list xmin ymin) (lat-lon->map-point min-coord))
  (match-define (list xmax ymax) (lat-lon->map-point max-coord))
  (define-values (xscale yscale) (values (/ width (- xmax xmin)) (/ height (- ymax ymin))))
  (define-values (xorigin yorigin) (values (- (* xmin xscale)) (- (* ymin yscale))))

  (send* dc
    (set-origin xorigin yorigin)
    (set-scale xscale yscale)
    (set-smoothing 'smoothed)
    (set-pen (send the-pen-list find-or-create-pen "black" (* 0.5 (/ 1 xscale)) 'solid))))

(define (make-timezone-bitmap tzdata min-coord max-coord width height)
  (define dc (new bitmap-dc% [bitmap (make-object bitmap% width height)]))
  (setup-dc dc min-coord max-coord)

  ;; Iterate over each feature (timezone) and render it
  (for ([feature  (in-list (hash-ref tzdata 'features))]
        [color (in-cycle color-map)])
    (send dc set-brush (send the-brush-list find-or-create-brush color 'solid))
    (draw-feature dc feature))
  (send dc get-bitmap))

(define timezone-data (call-with-input-file "./combined.json" read-json))
(define bm (make-timezone-bitmap timezone-data
                                 (list -13.008 61.481)
                                 (list 33.02 30.894)
                                 500 500))
(send bm save-file "timezone-map-3.png" 'png 100 #:unscaled? #t)
	#lang racket
	(require json)

	;; Example 0: Load and manipulate the Timezone GeoJSON file

	;; You will also need to download timezone data from:
	;;
	;; https://github.com/evansiroky/timezone-boundary-builder/releases

	;; Copyright (c) 2019 Alex Harsányi

	;; Permission is hereby granted, free of charge, to any person obtaining a
	;; copy of this software and associated documentation files (the "Software"),
	;; to deal in the Software without restriction, including without limitation
	;; the rights to use, copy, modify, merge, publish, distribute, sublicense,
	;; and/or sell copies of the Software, and to permit persons to whom the
	;; Software is furnished to do so, subject to the following conditions:

	;; The above copyright notice and this permission notice shall be included in
	;; all copies or substantial portions of the Software.

	;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	;; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	;; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
	;; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	;; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
	;; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
	;; DEALINGS IN THE SOFTWARE.


	(define timezone-data (time (call-with-input-file "./combined.json" read-json)))

	;; Extract a random sample from a json OBJECT -- this can be used on the
	;; timezone-data to obtain a smaller object which can be printed and inspected
	;; while developing the functions which manipulate the actual timezone data...
	(define (random-sample object [max-size 5])
	(cond
	((hash? object)
	;; for hash tables, copy all the keys, but simplify the values
	(for/hash ([(k v) (in-hash object)])
	(values k (random-sample v max-size))))
	((list? object)
	;; Short lists are copied directly, but we only sample MAX-SIZE random
	;; values from longer lists. In both cases the values themselves are
	;; further simplified.
	(let ([len (length object)])
	(if (> len max-size)
	(let ([samples (sort (build-list max-size (lambda (x) (random len))) <)])
	(for/list ([(x position) (in-indexed (in-list object))]
	#:when (member position samples))
	(random-sample x max-size)))
	(for/list ([x (in-list object)])
	(random-sample x max-size)))))
	(#t
	;; Any other objects are not simplified.
	object)))

	;; Every GeoJSON node will have type and properties keys
	(define (geojson-type node)
	(hash-ref node 'type #f))
	(define (geojson-properties node)
	(hash-ref node 'properties (lambda () (hash))))

	(define (geojson-features node)
	(let ([type (geojson-type node)])
	(if (equal? type "FeatureCollection")
	(hash-ref node 'features null)
	(error (format "geojson-features: bad node type: ~a" type)))))

	(define (geojson-geometry node)
	(let ([type (geojson-type node)])
	(if (equal? type "Feature")
	(hash-ref node 'geometry (lambda () (hash)))
	(error (format "geojson-geometry: bad node type: ~a" type)))))

	(define (geojson-coordinates node)
	(let ([type (geojson-type node)])
	(if (member type '("Point" "LineString" "Polygon" "MultiPoint" "MultiLineString" "MultiPolygon"))
	(hash-ref node 'coordinates null)
	(error (format "geojson-coordinates: bad node type: ~a" type)))))

	;; Count the number of points in a geometry GeoJSON node
	(define (geojson-geometry-point-count node)
	(let ([type (geojson-type node)]
	[coordinates (geojson-coordinates node)])
	(cond ((equal? type "Point")
	;; Coordinates is a single point
	1)
	((equal? type "LineString")
	;; List of points
	(length coordinates))
	((equal? type "Polygon")
	;; List of lists of points (main and holes. Count them all
	(for/fold ([result 0])
	([line (in-list coordinates)])
	(+ result (length line))))
	((equal? type "MultiPoint")
	;; List of points
	(length coordinates))
	((equal? type "MultiLineString")
	(for/fold ([result 0])
	([line (in-list coordinates)])
	(+ result (length line))))
	((equal? type "MultiPolygon")
	(for/fold ([result 0])
	([polygon (in-list coordinates)])
	(+ result
	(for/fold ([result 0])
	([line (in-list polygon)])
	(+ result (length line))))))
	(#t
	(error (format "Unknown geometry type: ~a" type))))))

	;; Count the number of points in a GeoJSON node and its sub-nodes.
	(define (geojson-point-count node)
	(let ((type (geojson-type node)))
	(cond ((equal? type "FeatureCollection")
	(for/fold ([result 0])
	([feature (in-list (geojson-features node))])
	(+ result (geojson-point-count feature))))
	((equal? type "Feature")
	(let ((geometry (geojson-geometry node)))
	(geojson-geometry-point-count geometry))))))

	;; return the timezone name stored in a GeoJSON feature
	(define (tz-name node)
	(let ((properties (geojson-properties node)))
	(hash-ref properties 'tzid #f)))

	;; Print a summary of the point count in the timezone data JSON
	(define (analyze-tz-point-count node)
	(define nzones (length (geojson-features node)))
	(define total (geojson-point-count node))
	(define tz-point-count
	(for/list ([feature (in-list (geojson-features node))])
	(list (tz-name feature) (geojson-point-count feature))))
	(set! tz-point-count
	(sort tz-point-count
	(lambda (a b)
	(match-define (list _ p1) a)
	(match-define (list _ p2) b)
	(> p1 p2))))
	(printf "Total point count: ~a, total zone count ~a~%" total nzones)
	(for ([tp (in-list tz-point-count)])
	(match-define (list name pcount) tp)
	(printf "~a ~a~%" name pcount)))
	#lang racket
	(require racket/draw)
	(define dc (new bitmap-dc% [bitmap (make-object bitmap% 250 250)]))
	(send* dc
	(set-pen (send the-pen-list find-or-create-pen "black" 5.0 'solid))
	(set-brush (send the-brush-list find-or-create-brush "red" 'solid))
	(draw-rectangle 10 10 (- 250 20) (- 250 20)))
	(define bm (send dc get-bitmap))
	(send bm save-file "example1.png" 'png)
	#lang racket
	(require racket/draw)

	(define path (new dc-path%))
	(send path move-to 1 0)
	(for ([p (in-range 0 (* 2 pi) (/ (* 2 pi) 5))])
	(define x (cos p))
	(define y (sin p))
	(send path line-to x y))
	(send path close)

	(define dc (new bitmap-dc% [bitmap (make-object bitmap% 250 250)]))
	(send* dc
	(set-smoothing 'smoothed)
	(set-scale 250/2 250/2)
	(set-origin 250/2 250/2)
	(set-pen (send the-pen-list find-or-create-pen "black" 0.01 'solid))
	(set-brush (send the-brush-list find-or-create-brush "red" 'solid))
	(draw-path path))
	(define bm (send dc get-bitmap))
	(send bm save-file "example3.png" 'png)
	#lang racket

	;; Example 4: Render the timezone data using a small color map

	;; You will also need to download timezone data from:
	;;
	;; https://github.com/evansiroky/timezone-boundary-builder/releases

	;; Copyright (c) 2019 Alex Harsányi

	;; Permission is hereby granted, free of charge, to any person obtaining a
	;; copy of this software and associated documentation files (the "Software"),
	;; to deal in the Software without restriction, including without limitation
	;; the rights to use, copy, modify, merge, publish, distribute, sublicense,
	;; and/or sell copies of the Software, and to permit persons to whom the
	;; Software is furnished to do so, subject to the following conditions:

	;; The above copyright notice and this permission notice shall be included in
	;; all copies or substantial portions of the Software.

	;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	;; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	;; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
	;; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	;; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
	;; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
	;; DEALINGS IN THE SOFTWARE.


	(require json racket/draw math/base)

	(define (lat-lon->map-point coordinates)
	(match-define (list lon lat _ ...) coordinates)
	(define-values (x y) (values (degrees->radians lon) (asinh (tan (degrees->radians lat)))))
	(list (/ (+ 1 (/ x pi)) 2) (/ (- 1 (/ y pi)) 2)))

	(define (draw-polygon dc polygons)
	(define path
	(for/fold ([path #f]) ([polygon (in-list polygons)] #:unless (null? polygon))
	(define sub-path (new dc-path%))
	(send/apply sub-path move-to (lat-lon->map-point (car polygon)))
	(for ([point (in-list (cdr polygon))])
	(send/apply sub-path line-to (lat-lon->map-point point)))
	(send sub-path close)
	(if path (begin (send path append sub-path) path) sub-path)))
	(and path (send dc draw-path path 0 0)))

	(define (draw-feature dc feature)
	(let* ([geometry (hash-ref feature 'geometry (lambda () (hash)))]
	[data (hash-ref geometry 'coordinates (lambda () null))])
	(case (hash-ref geometry 'type #f)
	(("Polygon") (draw-polygon dc data))
	(("MultiPolygon") (for ([polygon (in-list data)]) (draw-polygon dc polygon)))
	(else (printf "Skipping ~a geometry" (hash-ref geometry 'type #f))))))

	(define color-map
	(list (make-object color% 78 121 165)
	(make-object color% 241 143 59)
	(make-object color% 224 88 91)
	(make-object color% 119 183 178)
	(make-object color% 90 161 85)
	(make-object color% 237 201 88)
	(make-object color% 175 122 160)
	(make-object color% 254 158 168)
	(make-object color% 156 117 97)
	(make-object color% 186 176 172)))

	(define (make-timezone-bitmap tzdata width height)
	(define dc (new bitmap-dc% [bitmap (make-object bitmap% width height)]))
	(send* dc
	(set-scale width height)
	(set-smoothing 'smoothed)
	(set-pen (send the-pen-list find-or-create-pen "black" (* 0.5 (/ 1 width)) 'solid)))
	;; Iterate over each feature (timezone) and render it
	(for ([feature (in-list (hash-ref tzdata 'features))]
	[color (in-cycle (in-list color-map))])
	(send dc set-brush (send the-brush-list find-or-create-brush color 'solid))
	(draw-feature dc feature))
	(send dc get-bitmap))

	(define timezone-data (time (call-with-input-file "./combined.json" read-json)))
	(define bm (make-timezone-bitmap timezone-data 800 700))
	(send bm save-file "timezone-map.png" 'png 100 #:unscaled? #t)
	#lang racket
	(require json racket/draw math/base)

	;; Example 5: Render the timezone data using a a unique color for each color
	;; map

	;; You will also need to download timezone data from:
	;;
	;; https://github.com/evansiroky/timezone-boundary-builder/releases

	;; Copyright (c) 2019 Alex Harsányi

	;; Permission is hereby granted, free of charge, to any person obtaining a
	;; copy of this software and associated documentation files (the "Software"),
	;; to deal in the Software without restriction, including without limitation
	;; the rights to use, copy, modify, merge, publish, distribute, sublicense,
	;; and/or sell copies of the Software, and to permit persons to whom the
	;; Software is furnished to do so, subject to the following conditions:

	;; The above copyright notice and this permission notice shall be included in
	;; all copies or substantial portions of the Software.

	;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	;; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	;; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
	;; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	;; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
	;; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
	;; DEALINGS IN THE SOFTWARE.


	(define (lat-lon->map-point coordinates)
	(match-define (list lon lat _ ...) coordinates)
	(define-values (x y) (values (degrees->radians lon) (asinh (tan (degrees->radians lat)))))
	(list (/ (+ 1 (/ x pi)) 2) (/ (- 1 (/ y pi)) 2)))

	(define (draw-polygon dc polygons)
	(define path
	(for/fold ([path #f]) ([polygon (in-list polygons)] #:unless (null? polygon))
	(define sub-path (new dc-path%))
	(send/apply sub-path move-to (lat-lon->map-point (car polygon)))
	(for ([point (in-list (cdr polygon))])
	(send/apply sub-path line-to (lat-lon->map-point point)))
	(send sub-path close)
	(if path (begin (send path append sub-path) path) sub-path)))
	(and path (send dc draw-path path 0 0)))

	(define (draw-feature dc feature)
	(let* ([geometry (hash-ref feature 'geometry (lambda () (hash)))]
	[data (hash-ref geometry 'coordinates (lambda () null))])
	(case (hash-ref geometry 'type #f)
	(("Polygon") (draw-polygon dc data))
	(("MultiPolygon") (for ([polygon (in-list data)]) (draw-polygon dc polygon)))
	(else (printf "Skipping ~a geometry" (hash-ref geometry 'type #f))))))

	(define (tz-name node)
	(let ((properties (hash-ref node 'properties)))
	(hash-ref properties 'tzid #f)))

	(define (allocate-color id)
	(let* ((b (exact-floor (/ id 100)))
	(g (exact-floor (/ (- id (* b 100)) 10)))
	(r (exact-floor (- id (* b 100) (* g 10)))))
	(make-object color% (* r 28) (* g 28) (* b 28))))

	(struct tzdata (name id color) #:transparent)

	(define (allocate-tzdata node)
	(define next-id 1) ; start at 1, 0 is reserved for "no tz data", the oceans
	(for/list ([tznode (in-list (hash-ref node 'features))])
	(define name (tz-name tznode))
	(define id next-id)
	(set! next-id (add1 next-id))
	(define color (allocate-color id))
	(tzdata name id color)))

	(define (time-zone-color tz-data name)
	(for/first ([t (in-list tz-data)] #:when (equal? (tzdata-name t) name))
	(tzdata-color t)))

	(define color-map
	(list (make-object color% 78 121 165)
	(make-object color% 241 143 59)
	(make-object color% 224 88 91)
	(make-object color% 119 183 178)
	(make-object color% 90 161 85)
	(make-object color% 237 201 88)
	(make-object color% 175 122 160)
	(make-object color% 254 158 168)
	(make-object color% 156 117 97)
	(make-object color% 186 176 172)))

	(define (make-timezone-bitmap tzdata width height)
	(define tz-data (allocate-tzdata timezone-data))
	(define dc (new bitmap-dc% [bitmap (make-object bitmap% width height)]))
	(send* dc
	(set-scale width height)
	(set-smoothing 'smoothed)
	(set-pen (send the-pen-list find-or-create-pen "black" (* 0.5 (/ 1 width)) 'solid)))
	;; Iterate over each feature (timezone) and render it
	(for ([feature (in-list (hash-ref tzdata 'features))])
	(define color (time-zone-color tz-data (tz-name feature)))
	(send dc set-brush (send the-brush-list find-or-create-brush color 'solid))
	(draw-feature dc feature))
	(send dc get-bitmap))

	(define timezone-data (call-with-input-file "./combined.json" read-json))
	(define bm (make-timezone-bitmap timezone-data 800 500))
	(send bm save-file "timezone-map-2.png" 'png 100 #:unscaled? #t)
	#lang racket
	(require json racket/draw math/base)

	;; Example 6: Render a subset of the map

	;; You will also need to download timezone data from:
	;;
	;; https://github.com/evansiroky/timezone-boundary-builder/releases

	;; Copyright (c) 2019 Alex Harsányi

	;; Permission is hereby granted, free of charge, to any person obtaining a
	;; copy of this software and associated documentation files (the "Software"),
	;; to deal in the Software without restriction, including without limitation
	;; the rights to use, copy, modify, merge, publish, distribute, sublicense,
	;; and/or sell copies of the Software, and to permit persons to whom the
	;; Software is furnished to do so, subject to the following conditions:

	;; The above copyright notice and this permission notice shall be included in
	;; all copies or substantial portions of the Software.

	;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	;; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	;; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
	;; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	;; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
	;; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
	;; DEALINGS IN THE SOFTWARE.

	(define (lat-lon->map-point coordinates)
	(match-define (list lon lat _ ...) coordinates)
	(define-values (x y) (values (degrees->radians lon) (asinh (tan (degrees->radians lat)))))
	(list (/ (+ 1 (/ x pi)) 2) (/ (- 1 (/ y pi)) 2)))

	(define (draw-polygon dc polygons)
	(define path
	(for/fold ([path #f]) ([polygon (in-list polygons)] #:unless (null? polygon))
	(define sub-path (new dc-path%))
	(send/apply sub-path move-to (lat-lon->map-point (car polygon)))
	(for ([point (in-list (cdr polygon))])
	(send/apply sub-path line-to (lat-lon->map-point point)))
	(send sub-path close)
	(if path (begin (send path append sub-path) path) sub-path)))
	(and path (send dc draw-path path 0 0)))

	(define (draw-feature dc feature)
	(let* ([geometry (hash-ref feature 'geometry (lambda () (hash)))]
	[data (hash-ref geometry 'coordinates (lambda () null))])
	(case (hash-ref geometry 'type #f)
	(("Polygon") (draw-polygon dc data))
	(("MultiPolygon") (for ([polygon (in-list data)]) (draw-polygon dc polygon)))
	(else (printf "Skipping ~a geometry" (hash-ref geometry 'type #f))))))

	(define (tz-name node)
	(let ((properties (hash-ref node 'properties)))
	(hash-ref properties 'tzid #f)))

	(define color-map
	(list (make-object color% 78 121 165)
	(make-object color% 241 143 59)
	(make-object color% 224 88 91)
	(make-object color% 119 183 178)
	(make-object color% 90 161 85)
	(make-object color% 237 201 88)
	(make-object color% 175 122 160)
	(make-object color% 254 158 168)
	(make-object color% 156 117 97)
	(make-object color% 186 176 172)))

	(define (setup-dc dc min-coord max-coord)
	(define-values (width height) (send dc get-size))
	(match-define (list xmin ymin) (lat-lon->map-point min-coord))
	(match-define (list xmax ymax) (lat-lon->map-point max-coord))
	(define-values (xscale yscale) (values (/ width (- xmax xmin)) (/ height (- ymax ymin))))
	(define-values (xorigin yorigin) (values (- (* xmin xscale)) (- (* ymin yscale))))

	(send* dc
	(set-origin xorigin yorigin)
	(set-scale xscale yscale)
	(set-smoothing 'smoothed)
	(set-pen (send the-pen-list find-or-create-pen "black" (* 0.5 (/ 1 xscale)) 'solid))))

	(define (make-timezone-bitmap tzdata min-coord max-coord width height)
	(define dc (new bitmap-dc% [bitmap (make-object bitmap% width height)]))
	(setup-dc dc min-coord max-coord)

	;; Iterate over each feature (timezone) and render it
	(for ([feature (in-list (hash-ref tzdata 'features))]
	[color (in-cycle color-map)])
	(send dc set-brush (send the-brush-list find-or-create-brush color 'solid))
	(draw-feature dc feature))
	(send dc get-bitmap))

	(define timezone-data (call-with-input-file "./combined.json" read-json))
	(define bm (make-timezone-bitmap timezone-data
	(list -13.008 61.481)
	(list 33.02 30.894)
	500 500))
	(send bm save-file "timezone-map-3.png" 'png 100 #:unscaled? #t)