# Convert a edge/border into a set of points (==> polygons ==> masks)

Good Morning,

I whould like to kwon if it’s possible with SNAP to convert a layer/mask (or more specifically a edge) into a set of points ?

How could I know the passage between X/Y and lat/long ? (with some tie-grid points I guess)
Is it a bijection (ie X/Y --> lat/long and lat/long --> X/Y) ?

My goal is to create some polygons (using WKT) in order to select some areas which does not contain many clouds.
Once I have a polygon, is it possible to define the area inside and outside this polygon in order to get the areas with and without clouds ?

Thank you so much for your response.

As soon as you draw the polygon a corresponding mask is created. You can use it in several processors in a mask expression or in the band maths.

The image shows the drawn geometry (left), mask (middle), result of band math (right)

Thank you so much marpet !! ^^

And if I want to select the area outside of the polygon, what command should I write in the Band Maths operator ?

Furthermore, I would like to know if I can easily convert an edge into dots in order to create some polygons which will alow me to select the area inside/outside of this polygon ?

Regards,
aross

Just invert the expression:

``````geometry ? NaN : TOA_REFL_RED * 5
``````

You mean you want to do an edge detection on the data and based on the edges you want to create a mask/geometry?

I don’t really get your requirement yet.

But you can let run a filtering (see in menu: Raster \ Create Filtered band)

And based on the result you can use band math to create a new band which can be used as as mask.
``````Oa12_radiance > 60
``````mask_band ? sin(view_zenith_angle) * Oa14_radiance : cos(view_zenith_angle) * Oa14_radiance