<div style="font-family: Arial, sans-serif; font-size: 14px;"><span>Dear PostGIS users,</span><div><br></div><div><span>I have a <a href="https://data.jrc.ec.europa.eu/dataset/35fb1231-849b-4017-89d8-9cadbaf9d555" title="raster">raster</a> (of 100m pixel) of forest (val=1) / no forest (val=NULL) and a set of points that always fall inside forest areas.<br><br></span></div><div><span>I need to calculate the distance (up to 1km), in a given direction (let's say West, 300 radians), to the border of the forest patch where it falls in (distance A in fig.). Then, the distance from the previous forest border to the next forest border<span> (distance B in fig.)</span>, following the same direction. Like so:<br></span></div><div><br><img alt="Screenshot from 2023-10-24 18-19-16.png" class="proton-embedded" src="cid:4423d1e0@eloiribeiro.eu"><br><br></div><div><span>I was able to do this with the <span>following</span> steps:</span></div><div><span>1. Vectorize forest map. Note the ST_Union, to eliminate the borders of the raster tiles and avoid these being confused as forest border.</span></div><div><span></span></div><div style="font-family: "Droid Sans Mono", "monospace", monospace; font-weight: normal; line-height: 19px; white-space: pre; color: rgb(204, 204, 204); background-color: rgb(31, 31, 31);"><span><span style="color: rgb(206, 145, 120);">SELECT (ST_Dump(ST_Union(geom))).geom::geometry(Polygon,3035)</span></span><div><span style="color: rgb(206, 145, 120);">FROM (</span></div><div><span style="color: rgb(206, 145, 120);"> SELECT dp.*</span></div><div><span style="color: rgb(206, 145, 120);"> FROM storm.forest_2020_europe, </span></div><div><span style="color: rgb(206, 145, 120);"> LATERAL ST_DumpAsPolygons(rast) AS dp</span></div><div><span style="color: rgb(206, 145, 120);"> ) As foo</span></div><div><span style="color: rgb(206, 145, 120);">GROUP BY val</span></div><span><span style="color: rgb(206, 145, 120);">HAVING val = 1;</span></span></div><div><span></span></div><div><br></div><div><span>2. Create Linestring from point, as starting point, following 300 radians and 1km length.</span></div><div><span></span></div><div style="font-family: "Droid Sans Mono", "monospace", monospace; font-weight: normal; line-height: 19px; white-space: pre; color: rgb(204, 204, 204); background-color: rgb(31, 31, 31);"><span><span style="color: rgb(206, 145, 120);">SELECT gid, </span></span><div><span style="color: rgb(206, 145, 120);"> '</span><span>1km </span><span style="color: rgb(181, 206, 168);">300</span><span> rad</span><span style="color: rgb(206, 145, 120);">', </span></div><div><span style="color: rgb(206, 145, 120);"> ST_MakeLine(geom, ST_Translate(geom, sin(300)*1000, cos(300)*1000)) AS geom</span></div><span><span style="color: rgb(206, 145, 120);">FROM storm.point;</span></span></div><div><span></span></div><div><br></div><div><span>3. Overlay Linestring from step 2 with vectorize forest map and get the distances from Linestring segments. This part has too much SQL to put it here. I have used <span>ST_Intersection and ST_Difference, and then ST_Touches to make sure the segment touches the first point, for the first distance and <span><span>touches</span></span> the EndPoint of the first segment to get the second distance.</span><br></span></div><div><br></div><div><span>This at national level worked just fine. But now at continent level, the resulting vectorized polygons of the forest patches are just too big and takes forever to vectorize. So, I need to do this directly with the raster forest map.</span></div><div><br></div><div><span>Any hints how could this be accomplished?<br></span></div><span></span><br>Thanks!<br><br>Cheers,<br></div><div style="font-family: Arial, sans-serif; font-size: 14px;"><br></div>
<div class="protonmail_signature_block " style="font-family: Arial, sans-serif; font-size: 14px;">
<div class="protonmail_signature_block-user "><div><div>Eloi<br></div></div><div><br></div></div>
<div class="protonmail_signature_block-proton protonmail_signature_block-empty">
</div>
</div>