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ImageryLayer : get pixel values in polygon

ClémentLaskar

Hello,

I'm trying to build a raster analysis tool :

- users can view raster on their web browser

- they can draw polygons of interest on the map

- they can query for values of the raster's pixels in the polygons extents and get (for each drawn polygon) :

- mean of raster value in the polygon

- histogram of raster value in the polygon

I thought I could use Javascript API to do this but I'm not able to find any method to get ImageryLayer pixel values intersecting a polygon. Is there any ? Furthemore, it seems like if the polygon is not visible on the map, the raster is neither. So accessing pixel value of a polygon which is not visible is impossible. Should I do this another way, using the REST API of the service ?

Thanks for your advices !

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ClémentLaskar

Hi John,

Thanks a lots for your codepen, i'll try it with my datas and see if it works !

JohnGrayson

You can use the mosaicRule and renderingRule to control the pixels used in the calculations. For the histogram, applying a proper mosaicRule and renderingRule is vital to make sure your stats reflect the necessary data ranges and values. It will all depend on the type of data and how its configured and published. I normally like to remap the data into simple meaningful groupings to make it simpler for the users of the apps to make sense of the data. Here's a quick codepen showing how to make the call and retrieve the results; I hope this helps.

ClémentLaskar

Hi John and thanks for your answer. Looking at the doc of Statistics and Histograms in the REST API, I don't understand what exactly contains the "histograms" response attribute and how are they customizable? I don't see any query attributes to specify the classes breaks I want to get, are there any ?

Thanks a lot !

JohnGrayson

@ClémentLaskar if your raster data is consumed via an Imagery Layer (Image Service) you can use a direct REST call to the service computeStatisticsHistograms endpoint to do what you need.

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