Sorry
I missed sending this to the entire group:
Assuming you send the request in the form:
http://myserver.com/getarea.php?xmin=-100&ymin=40&xmax=-99&ymax=41
getarea.php is:
<?php
header("Content-Type: text/xml");
$username = 'xxx';
$dbGeomName = 'XXX';
$password = 'yyy';
$hostname = 'mylhost';
//get URL parameters
$xmin = intval($_GET['xmin']);
$xmax = intval($_GET['xmax']);
$ymin = intval($_GET['ymin']);
$ymax = intval($_GET['ymax']);
//I assume since you are using Google Maps
$srid = 4326;
$tablename = 'whateverMyTableIs';
//intersection polygon to clip out data where useful
$intersectPolygon = 'GeometryFromText(\'POLYGON(('.$xmin.'
'.$ymin.','.$xmax.' '.$ymin.','.$xmax.' '.$ymax.','.$xmin.'
'.$ymax.','.$xmin.' '.$ymin.'))\','.$srid.')';
//connect to db
$my_pg_connect = pg_Connect('host='.$hostname.' dbname='.$dbGeomName.'
user='.$username.' password='.$password) or die ('Can\'t connect to
database '.$dbGeomName);
$mySQL= 'SELECT
area(ST_intersection(the_geom_ca_albers,transform('$intersectPolygon.',find_srid(\'\',\''.$tablename.'\',\'the_geom_ca_albers\'))))
AS area FROM '.$tablename;
//execute sql command
$my_result_set = pg_Exec($my_pg_connect, $mySQL) or die
(pg_ErrorMessage());
//get number of rows retrieved
$numRecs = pg_NumRows($my_result_set);
$resultArray = pg_Fetch_Array($my_result_set, 0);
print $resultArray['area']);
//close db connection
pg_Close($my_pg_connect);
?>
This should return the area within your viewport in the map units of
your table (the_geom_ca_albers).
I didn't exactly test this - I took a small section of some existing
code. Let me know if there are issues.
For a nice tutorial of what is going on here see:
http://www.carto.net/papers/svg/postgis_geturl_xmlhttprequest/
Bruce
Jennifer Strahan wrote:
Yes, PHP.
Thanks,
Jennifer
Bruce Rindahl wrote:
How are you connecting with the database? PHP?
Bruce
Jennifer Strahan wrote:
Hi Everyone,
I'm hoping someone can offer guidance on writing an sql statement.
I'm working on a Google maps interface to display protected lands in
California. As the user moves the map, I'd like to calculate the
total area of protected lands within the current map view. I'm able
to get the map bounds as lat/lon and pass that to the script. I'm
not sure how to do processing though. Do I need to use ST_Union to
get the union of the map frame and the polygons, then get the area
of that? Any examples on how to write the SQL would be very
helpful. By the way I have multiple geometry columns in my table,
one that is CA teale albers (the_geom_ca_albers), and one that is
web mercator (the_geom_google).
Thanks,
Jennifer
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