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Geospatial_analysis_Yale-NUS.md

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+<p align="center"> <b>Geospatial Software Analysis - An Introduction to Google Earth Engine</b> </p>
+
+<br><br><br><br><br><br><br><br>
+
+
+<p align="center"> <b>TC Chakraborty</b>   </p>
+
+<p align="center"> <b>Yale School of Forestry & Environmental Studies</b>   </p>
+
+<p align="center"> <b>Yale Data Driven Solutions Group</b>   </p>
+
+<br><br><br><br>
+
+
+<p align="center">  <b>March 16, 2018</b>  </p>
+<br><br>
+<br><br><br><br>
+<br><br><br><br><br><br><br><br>
+
+---
+
+<p align="center"> https://github.com/datadrivenyale/day-of-data-2.0 </p>
+
+---
+<br><br><br><br><br><br><br>
+
+# Agenda
+
+##### Introduction to Geospatial Analysis
+##### Data Types
+##### The Google Earth Engine platform
+##### Basic functions
+##### Variable types
+##### Geometry declaration
+##### Functions and mapping
+##### Operations on Geometries
+##### Features and Feature Collections
+##### Operations on Features
+##### Filters
+##### Operations on Images
+##### Operations on Image Collections
+##### Importing and exporting Data
+##### Conclusion and resources
+
+---
+
+# Introduction
+Collection, visualization, and analysis of geographical or spatial data.
+
+# Data types
+
+- Vector data represent lat-long coordinates
+
+- Raster data comprises of pixels with associated values
+
+---
+
+
+- Points
+
+![Points](https://github.com/datadrivenyale/day-of-data-2.0/blob/master/5-Geospatial%20analysis/images/points-vector.png "Points")
+
+- Lines
+
+![Lines](https://github.com/datadrivenyale/day-of-data-2.0/blob/master/5-Geospatial%20analysis/images/line-vector.png "Lines")
+
+- Polygons
+
+![Polygons](https://github.com/datadrivenyale/day-of-data-2.0/blob/master/5-Geospatial%20analysis/images/polygon-vector.png "Polygons")
+
+- Raster layers/bands
+
+![Raster](https://github.com/datadrivenyale/day-of-data-2.0/blob/master/5-Geospatial%20analysis/images/Map-Algebra.png "Raster")
+
+
+---
+
+# Google Earth Engine platform
+
+[Code Editor](https://code.earthengine.google.com/ "Earth Engine Code Editor")
+
+- Cloud-based platform for planetary scale geospatial analysis
+- Uses Google's computational resources to reduce processing time
+- Massive archive of remote sensing data 
+- 200 public datasets 
+- greater than 4000 new images every day 
+- greater than 5 million images 
+- greater than 5 petabytes of data
+
+Source: Google Earth Engine User summit
+
+---
+
+![Code Editor](https://github.com/datadrivenyale/day-of-data-2.0/blob/master/5-Geospatial%20analysis/images/EE.png "Code Editor")
+
+---
+
+# Basic Functions
+
+### Declaring variables 
+```javascript
+var varname = Containerforvariabletype(variable name); 
+```
+###  Centering map
+```javascript
+Map.setCenter(long, lat, zoom level);
+```
+>Zoom level varies from 0 (no zoom) to 20 (highest zoom level)
+
+### Displaying metadata
+```javascript
+print(variable name) 
+```
+### Adding a layer to the map
+```javascript
+Map.addLayer(VARIABLENAME);
+```
+
+---
+
+# Variable types in Earth Engine
+
+### Strings  
+
+```javascript
+var var_String = ee.String("This is a string. Or is it? It is."); 
+```
+### Numbers
+```javascript
+var var_Numbers = ee.Number(5);
+```
+
+### Arrays
+```javascript
+var var_Array = ee.Array([[5, 2, 3],  [-2, 7, 10],  [6, 6, 9]]); 
+```
+
+### Lists
+```javascript
+var var_List = ee.List([5, "five" , 6, "six"]); 
+```
+### Dictionaries
+```javascript
+var var_Dictionary = ee.Dictionary({five: 5 , six: 6}); 
+```
+
+### And the fun stuff
+- Geometries
+- Features
+- Feature Collections
+- Images
+- Image Collections
+
+---
+
+# Geometries – declaration and types
+
+### Points
+```javascript
+var var_Point = ee.Geometry.Point(0, 45);
+```
+### Multi Points
+```javascript
+var var_MultiPoint = ee.Geometry.MultiPoint(0, 45, 5,6, 70,-56);
+```
+### Line String
+```javascript
+var var_LineString = ee.Geometry.LineString([[0, 45], [5,6], [70,-56]]);
+```
+### Multi Line String
+```javascript
+var var_MultiLineString = ee.Geometry.MultiLineString([[[0, 45], [5,6], [70,-56]], [[0, -45], [-5,-6], [-70,56]]]);
+```
+### Linear Ring
+```javascript
+var var_LinearRing = ee.Geometry.LinearRing(0, 45, 5,6, 70,-56, 0,45);
+```
+### Rectangle
+```javascript
+var var_Rectangle = ee.Geometry.Rectangle(0, 0, 60,30);
+```
+### Polygon
+```javascript
+var var_Polygon = ee.Geometry.Polygon([[[0, 0], [6,3], [5, 5], [-30,2], [0,0]]]);
+```
+### Multi Polygon
+```javascript
+var var_MultiPolygon = ee.Geometry.MultiPolygon([ee.Geometry.Polygon([[0, 0], [6, 3], [5, 5], [-30, 2], [0,0]]), ee.Geometry.Polygon([[0, 0], [-6, -3], [-5, -5], [30, -2], [0, 0]])]);
+```
+
+---
+
+# Features and Feature Collections
+
+- Features are geometries associated with specific properties
+- Feature Collections are groups of features
+
+
+![Singapore map by GRC](https://github.com/datadrivenyale/day-of-data-2.0/blob/master/5-Geospatial%20analysis/images/GRC.png "Singapore Map by GRC")
+
+---
+
+# Functions and mapping
+
+- A set of instructions to perform a specific task
+```javascript
+function  function_Name(Arguments) {statements};
+```
+### Call function
+```javascript
+var result = function_Name(Input);
+```
+
+### Map function over Feature or Image Collection
+```javascript
+var result = Input.map(function_Name);
+```
+
+---
+
+
+# Operations on Geometries
+
+[Geometry operations](https://code.earthengine.google.com/d5d2db5aa4bea6bd94355a39e1f42a3f "EE Geometry operations")
+
+### Find area of geometry
+```javascript
+var Geometry_area = var_Geometry.area();
+```
+### Find length of line
+```javascript
+var Line_length = var_LineString.length();
+```
+### Find perimeter of geometry
+```javascript
+var Geometry_perimeter = var_Geometry.perimeter();
+```
+
+### Reduce number of vertices in geometry
+```javascript
+var SimplifiedGeometry = var_Geometry.simplify(100);
+```
+### Find centroid of geometry
+```javascript
+var Centroid = var_Geometry.centroid();
+```
+### Create buffer around geometry
+```javascript
+var Buffer = var_Geometry.buffer(100);
+```
+### Find bounded rectangle of the Geometry
+```javascript
+var BoundedGeometry = var_Geometry.bounds();
+```
+### Find the smallest envelope that can envelop the Geometry
+```javascript
+var Convexhull_Geometry = var_Geometry.convexHull();
+```
+### Find common area between two or more geometries
+```javascript
+var Inter_geometry = var_Geometry1.intersection(var_Geometry2);
+```
+### Find area that includes two or more geometries
+```javascript
+var Union_geometry = var_Geometry1.union(var_Geometry2);
+```
+---
+# Operations on Features
+
+[Feature operations](https://code.earthengine.google.com/1cd4cb760f71a56dce1cabcf44feec27 "EE Feature operations")
+
+### Set property name and value of geometry to create a feature
+```javascript
+var var_Feature = ee.Feature(var_Geometry, {Name: "Feature name", Size: 500};
+```
+### Create a new feature from existing feature while renaming a property
+```javascript
+var var_Featurenew = var_Feature.select(["Name"], ["Descriptor"]);
+```
+### Extract values of a property from a Feature 
+```javascript
+var values = var_Feature.get(''Size'');
+```
+---
+
+# Filters
+
+### Creator a filter for values of a property 
+
+```javascript
+var BFilter = ee.Filter.eq(Property_name, Value);
+```
+>or .neq , .gt , .gte , .lt , and .lte
+
+### Create a filter based on maximum difference from a threshold
+
+```javascript
+var DiffFilter = ee.Filter.maxDifference(threshold, Property_name, Value);
+```
+
+### Create a text filter
+
+```javascript
+var TxtFilter = ee.Filter.stringContains( Property_name, StringValue);  
+```
+
+>or .stringStartsWith, and .stringEndsWith
+
+### Create a range filter
+
+```javascript
+var RangeFilter = ee.Filter.rangeContains( Property_name, StringValue, MinValue, MaxValue);
+```
+  
+### Create a list filter to check for certain values
+
+```javascript
+var ListFilter = ee.Filter.listContains(Property_name, Value1, Property_name2, Value2); 
+```
+>.inList to test against list of values
+
+### Create a filter of dates
+
+```javascript
+var DateFilter = ee.Filter.calendarRange(StartDate, StopDate);
+```
+
+### Create a filter for particular days of the year
+
+```javascript
+var DayFilter = ee.Filter.dayOfYear(startDay, StopDay);
+```
+
+### Create a filter to subset geospatial data
+
+```javascript
+var BoundsFilter= ee.Filter.bounds(GeometryorFeature);
+```
+### Combining and inversing filters
+
+```javascript
+var NewFilter=ee.Filter.and(Listoffilters);
+var NewFilter=ee.Filter.or(Listoffilters);
+var inverseFilter = ee.Filter.not(filter);
+```
+---
+# Operations on Images
+
+[Image operations](https://code.earthengine.google.com/54c72f1d74cb42e7ed1245f1511562bb "EE Image operations")
+
+### Selecting the bands of an image 
+```javascript
+var band = var_Image.select(band name);
+```
+### Creating masks
+```javascript
+var mask =var_Image.eq(value); 
+```
+>or .neq or .gt or .gte or .lt or .lte
+### Applying masks
+```javascript
+var masked =var_Image.mask(mask);
+```
+
+### Pixelwise calculation
+```javascript
+var results =var_Image.sum(value); 
+```
+>or .subtract ,    .multiply ,    .divide ,    .max , .min ,  .abs ,  .round ,  .floor ,  .ceil ,  .sqrt ,  .exp,  .log, .log10, .sin ,  .cos ,  .tan ,  .sinh ,  .cosh ,  .tanh ,  .acos, .asin 
+
+### Shift pixels of an image
+```javascript
+newImage = oldImage.leftShift(valueofshift);                       
+```
+>or .rightShift
+
+### Create a single value from an image by applying a reducer based on regions of interest
+
+```javascript
+var outputDictionary = var_Image.reduceRegion(Reducer, var_Geometry, scale);
+```
+
+---
+
+# Operations on Image Collections
+
+### Select the first n numbers of images in a collection (based on property)
+
+```javascript
+var SelectedImages =var_ImCollection.limit (n, Property_name, Order);
+```
+
+### Select images in collection based on particular properties
+
+```javascript
+var SelectedImages = var_ImCollection.filterMetadata (Property_name, Relation , Value);
+```
+>Relations could be "equals", "less_than", "greater_than", "starts_with", "ends_with", and "contains"
+
+### Select images within date range
+```javascript
+var SelectedImages = var_ImCollection.filterDate (StartDate, StopDate);
+```
+
+### Select images within Geometry
+```javascript
+var SelectedImages = var_ImCollection.filterBounds (var_Geometry);
+```
+
+### Perform pixelwise calculations for all images in collection
+```javascript
+var sumofimages = var_ImCollection.sum();       
+```
+>or .product, .max, .min, .mean, .mode, .median, and .count     
+
+### Create composite of images in collection with the last image on top
+
+```javascript
+var mosaicofimages = var_ImCollection.mosaic();       
+```
+---
+# Importing and exporting data
+
+[Image to table example](https://code.earthengine.google.com/7ba00e4d20acfdb3973bb0263757ecd7 "Image to table example")
+
+[Timelapse example](https://code.earthengine.google.com/3f9c9d57c08ac12f60d0f9f213a0d359 "Timelapse example")
+### Export image, video or table to Google Drive, Asset, or Google Cloud
+
+```javascript
+Export.image.toDrive({
+  collection: var_Image, description: 'FileName', region: var_Geometry, scale: 1000}
+});
+```
+>or image.toCloudStorage, image.toAsset, table.toDrive, table.toCloudStorage, video.toCloudStorage, and video.toDrive
+
+---
+
+# Conclusion and resource
+
+[Night Lights example](https://code.earthengine.google.com/2859884e8ea9b116c2ae24c3f95ec8cb "Night Lights example") 
+- Adapted from Prof. Dana Tomlin's notes
+
+### Resources
+[Google Earth Engine API documentation](https://developers.google.com/earth-engine/ "Google Earth Engine API documentation")
+
+[Google Earth Engine Developers forum](https://groups.google.com/forum/#!forum/google-earth-engine-developers "Google Earth Engine Developers forum")
+
+[Example scripts from Prof. Dana Tomlin's handouts for his course on Geospatial Software Design](https://github.com/EEYale/example-scripts "Example scripts from Prof. Dana Tomlin's handouts for his course on Geospatial Software Design")
+
+- tc.chakraborty@yale.edu