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systemapic / pile

PostGIS tile server
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Raster calc functions #45

Open knutole opened 8 years ago

knutole commented 8 years ago

We need to implement a few raster calculations:

1. min, max, avg per raster

In order to create this graph, we need to pull min, max, avg of each day (ie. each raster): screen shot 2016-04-18 at 3 10 24 pm Also need to create a js wrapper fn to concat all raster stats into one array (for each year, or for give range).

2. min, max, avg per raster, by geojson mask

Same as above, but instead of whole raster, only over an area (geojson mask).

knutole commented 8 years ago

Hi @strk . Working on this little problem, quite difficult for me, perhaps very simple for you?

So, to explain the query that I need to make:

We have a set of rasters (aka datasets in a cube) for which I need to query the snow cover fraction. The rasters are Byte type, and the classification is shown below. The snow cover fraction classified between values 100-200 in the raster. So I need to query the raster (either the whole thing, or within a GeoJSON mask) and get the average snow cover fraction of all pixels (ie. the value between 100 and 200).

The problem with querying ST_SummaryStats on the raster, is that it includes values below 100 and above 200, while we only want to take into consideration the pixels with values within the 100-200 range.

I'm currently experimenting with this: 

SELECT rid, band, (stats).* FROM (SELECT rid, band, ST_SummaryStats(rast, band) As stats FROM file_pszjkuicfjvxvizbygbq CROSS JOIN generate_series(1,1) As band ) As foo;

Another problem with this approach, is that the raster is cut (due to pretiling) into 640 rows. So I'm getting results per row, and not for the whole.

The end result should simply be the SCF, ie. the average value of all pixels within 100-200 range (subtracted by 100 to get %).

If you have time, @strk, could you help point me in the right direction? (By the way, will get back to you in the end of the week with some exciting developments with Systemapic...)

References

Byte type classification of Snow Cover Fraction rasters (100-200 is area for calculating scf):
0   Night 
1   UNC 
2   UNC 
3   UNC 
4   UNC 
5   UNC 
6   UNC 
7   UNC 
8   UNC 
9   UNC 
10  Outside/Masked 
11  Outside/Masked 
12  Outside/Masked 
13  Outside/Masked 
14  Outside/Masked 
15  Outside/Masked 
16  Outside/Masked 
17  Outside/Masked 
18  Outside/Masked 
19  Outside/Masked 
20  Water 
21  Water 
22  Water 
23  Water 
24  Water 
25  Water 
26  Water 
27  Water 
28  Water 
29  Water 
30  Clouds 
31  Clouds 
32  Clouds 
33  Clouds 
34  Clouds 
35  Clouds 
36  Clouds 
37  Clouds 
38  Clouds 
39  Clouds 
40  Outside/Masked 
41  Outside/Masked 
42  Outside/Masked 
43  Outside/Masked 
44  Outside/Masked 
45  Outside/Masked 
46  Outside/Masked 
47  Outside/Masked 
48  Outside/Masked 
49  Outside/Masked 
50  Bare Ground 
51  Bare Ground 
52  Bare Ground 
53  Bare Ground 
54  Bare Ground 
55  Bare Ground 
56  Bare Ground 
57  Bare Ground 
58  Bare Ground 
59  Bare Ground 
60  Forest 
61  Forest 
62  Forest 
63  Forest 
64  Forest 
65  Forest 
66  Forest 
67  Forest 
68  Forest 
69  Forest 
70  Glacier 
71  Glacier 
72  Glacier 
73  Glacier 
74  Glacier 
75  Glacier 
76  Glacier 
77  Glacier 
78  Glacier 
79  Glacier 
80  UNC 
81  UNC 
82  UNC 
83  UNC 
84  UNC 
85  UNC 
86  UNC 
87  UNC 
88  UNC 
89  UNC 
90  UNC 
91  UNC 
92  UNC 
93  UNC 
94  UNC 
95  UNC 
96  UNC 
97  UNC 
98  UNC 
99  UNC 
100 Bare Ground 
101 0-10% Snow 
102 0-10% Snow 
103 0-10% Snow 
104 0-10% Snow 
105 0-10% Snow 
106 0-10% Snow 
107 0-10% Snow 
108 0-10% Snow 
109 0-10% Snow 
110 10-20% Snow 
111 10-20% Snow 
112 10-20% Snow 
113 10-20% Snow 
114 10-20% Snow 
115 10-20% Snow 
116 10-20% Snow 
117 10-20% Snow 
118 10-20% Snow 
119 10-20% Snow 
120 20-35% Snow 
121 20-35% Snow 
122 20-35% Snow 
123 20-35% Snow 
124 20-35% Snow 
125 20-35% Snow 
126 20-35% Snow 
127 20-35% Snow 
128 20-35% Snow 
129 20-35% Snow 
130 20-35% Snow 
131 20-35% Snow 
132 20-35% Snow 
133 20-35% Snow 
134 20-35% Snow 
135 35-50% Snow 
136 35-50% Snow 
137 35-50% Snow 
138 35-50% Snow 
139 35-50% Snow 
140 35-50% Snow 
141 35-50% Snow 
142 35-50% Snow 
143 35-50% Snow 
144 35-50% Snow 
145 35-50% Snow 
146 35-50% Snow 
147 35-50% Snow 
148 35-50% Snow 
149 35-50% Snow 
150 50-65% Snow 
151 50-65% Snow 
152 50-65% Snow 
153 50-65% Snow 
154 50-65% Snow 
155 50-65% Snow 
156 50-65% Snow 
157 50-65% Snow 
158 50-65% Snow 
159 50-65% Snow 
160 50-65% Snow 
161 50-65% Snow 
162 50-65% Snow 
163 50-65% Snow 
164 50-65% Snow 
165 65-80% Snow 
166 65-80% Snow 
167 65-80% Snow 
168 65-80% Snow 
169 65-80% Snow 
170 65-80% Snow 
171 65-80% Snow 
172 65-80% Snow 
173 65-80% Snow 
174 65-80% Snow 
175 65-80% Snow 
176 65-80% Snow 
177 65-80% Snow 
178 65-80% Snow 
179 65-80% Snow 
180 80-90% Snow 
181 80-90% Snow 
182 80-90% Snow 
183 80-90% Snow 
184 80-90% Snow 
185 80-90% Snow 
186 80-90% Snow 
187 80-90% Snow 
188 80-90% Snow 
189 80-90% Snow 
190 90-99% Snow 
191 90-99% Snow 
192 90-99% Snow 
193 90-99% Snow 
194 90-99% Snow 
195 90-99% Snow 
196 90-99% Snow 
197 90-99% Snow 
198 90-99% Snow 
199 90-99% Snow 
200 100% Snow 
201 UNC 
202 UNC 
203 UNC 
204 UNC 
205 Wet snow 
206 UNC 
207 UNC 
208 UNC 
209 UNC 
210 Dry Snow 
211 UNC 
212 UNC 
213 UNC 
214 UNC 
215 UNC 
216 UNC 
217 UNC 
218 UNC 
219 UNC 
220 UNC 
221 UNC 
222 UNC 
223 UNC 
224 UNC 
225 UNC 
226 UNC 
227 UNC 
228 UNC 
229 UNC 
230 UNC 
231 UNC 
232 UNC 
233 UNC 
234 UNC 
235 UNC 
236 UNC 
237 UNC 
238 UNC 
239 UNC 
240 UNC 
241 UNC 
242 UNC 
243 UNC 
244 UNC 
245 UNC 
246 UNC 
247 UNC 
248 UNC 
249 UNC 
250 UNC 
251 UNC 
252 UNC 
253 UNC 
254 UNC 
255 Ice on Lake
knutole commented 8 years ago

Making progress on this, so no worries. :)