[mapserver-users] distance between line and a given point usingmapscript

[Mark Brooks]

I got the looping through each result.  However, all distances are
calculated to -1, which I know can't be right.  In debugging, I'm also
echo'ing the shape index for each result, but it's always the same.  Am I
constructing the layer correctly?


// create array of points from database query results.
for ($i=0; $row=mysql_fetch_assoc($result); $i++){

        $points[$row['snum']][$i]['lat'] = $row['lat'];
        $points[$row['snum']][$i]['lon'] = $row['lon'];

} // End loop through points

// create map object
$map = ms_newMapObj('wms.map');

// create new layer for hurricane tracks.
$my_layer = ms_newLayerObj($map);

// set some fields for this new layer
$my_layer->set("toleranceunits","miles");
$my_layer->set("tolerance","20");

// Create new class and add TEMPLATE.
$my_class = ms_newClassObj($my_layer);
$my_class->set("template",'query_template.html');

// Loop through points, create line for each storm, and add track points
to new line object.
while (list($snum,$coordinates)=each($points)){

        // Create new line object
        $my_line = ms_newLineObj();

        // Loop through each point coordinate for this snum
        while (list($num,$coordinate)=each($coordinates)){

                // Create new point object
                $my_point = ms_newpointObj();
                $my_point->setXY($coordinate['lon'],$coordinate['lat']);

                // Add point to line object
                $my_line->add($my_point);

        } // done adding this storm's points to the line object

        // Now create a new shape object
        $my_shape = ms_newShapeObj(MS_SHAPE_LINE);
        $my_shape->add($my_line);

        // Add feature to the layer
        $my_layer->addFeature($my_shape);

} // end creating and adding points to line objects and line objects to
the layer.

// Draw map.
$map->draw();

// Make a new point object that will be our reference point.
$my_ref_point = ms_newpointObj();
$my_ref_point->setXY(-78.7,35.4);  // user-entered coordinates of where we
are querying from.

// Run a point query on the line object layer.
if (@$my_layer->queryByPoint($my_point,MS_MULTIPLE,-1)==MS_SUCCESS){

        // Loop through results.
        $num_results = $my_layer->getNumResults();
        echo "# results = $num_results\n\n";

        // Loop through each result
        for ($num=0; $num<$num_results; $num++){
                echo "result # $num:\n";

                // Get this result
                $my_result = $my_layer->getResult($num);

                //$my_shape =
$my_layer->getShape($my_result->tileindex,$my_result->shapeindex);
 // Get the shape
                echo "shapeindex = ".$my_result->shapeindex."\n";
                $my_shape = $my_layer->getFeature($my_result->shapeindex);
 // Get the feature
                echo "distanceToShape =
".$my_ref_point->distanceToShape($my_shape)."\n\n"; //
calculate distance from ref point to feature

        }
}



On Mon, July 27, 2009 11:54 pm, Steve Lime wrote:
> There are lots of samples that show you how to loop through a set of
> search
> results. There's a getNumResults() method for layer objects and then a
> getResult()
> method to retrieve each one individually.
>
> Steve
>
>>>> Mark Brooks <mark_brooks at ncsu.edu> 07/27/09 9:50 AM >>>
> Steve,
>
> This is a huge help.  The only thing I had not figured out was the
> 'toleranceunits' and 'tolerance' fields.  I appreciate your help!
>
> I intend to add many, possible hundreds, lines to a layer.  Then query
> it with a given reference point.  How do I get the number of results and
> then loop through each one?
>
> Best Regards,
> Mark
>
>
> Steve Lime wrote:
>>> How do I query a layer with one or more line features to find all
>>> features with X miles of a given point?
>>
>> Your line layer should like so:
>>
>>   LAYER
>>     NAME 'lines'
>>     TYPE LINE
>>     ...other junk...
>>     TEMPLATE 'dummy' # to be queryable
>>     TOLERANCEUNITS MILES
>>     TOLERANCE X
>>   END
>>
>> Then in mapscript you'd do a
>>
>>   $my_layer->queryByPoint($my_point, MS_MULTIPLE, -1);
>>
>> The buffer parameter is used to override a layer tolerance so setting to
>> -1 tells
>> the method to ignore it.  If you do use it then it's given in the units
>> of the layer
>> being searched (before any projection).
>>
>> Does that help?
>>
>> Steve
>>
>>>>> Mark Brooks <mark_brooks at ncsu.edu> 07/24/09 3:26 PM >>>
>> I'm trying to create several new line objects and then find the lines
>> that are within x miles of a given point.  (i.e., how far away a given
>> point is from the track of a hurricane or the path of a ship).  I'm
>> having some difficulties and I hope someone can help.
>>
>> How do I query a layer with one or more line features to find all
>> features with X miles of a given point?
>>
>> Here is how I'm approaching the problem in PHP:
>>
>> // Test array of points.  This is used to make a line.
>> $points[0]['lat'] = 35.5;
>> $points[0]['lon'] = -78.8;
>> $points[1]['lat'] = 36.5;
>> $points[1]['lon'] = -79.8;
>> $points[2]['lat'] = 37.5;
>> $points[2]['lon'] = -80.1;
>>
>> // make new map object.
>> $map = ms_newMapObj('mapdata/mymap.map');
>>
>> // Create new line
>> $my_line = ms_newLineObj();
>>
>> // Loop through points, and add to the line
>> while (list(,$coordinate)=each($points)){
>>
>>          // Create new point object
>>          $my_point = ms_newpointObj();
>>          $my_point->setXY($coordinate['lon'],$coordinate['lat']);
>>
>>          // Add point to line object
>>          $my_line->add($my_point);
>> }
>>
>> // Now create a new shape
>> $my_shape = ms_newShapeObj(MS_SHAPE_LINE);
>> $my_shape->add($my_line);
>>
>> // create new layer
>> $my_layer = ms_newLayerObj($map);
>>
>> // set some fields for this new layer
>> //$my_layer->set("units","miles");  // does not seem to work as expected
>>
>> // Create new class and add TEMPLATE.  This is required for queries on
>> the layer to work?
>> $my_class = ms_newClassObj($my_layer);
>> $my_class->set("template",'/home/www/html/query_template.html');
>>
>> // Add feature to the layer
>> $my_layer->addFeature($my_shape);
>>
>> // Draw map. Query doesn't work if I don't do this now.
>> $map->draw();
>>
>> // Make a new point object that will be our ref point
>> // to check how far away the line is from this point.
>> $my_point = ms_newpointObj();
>> $my_point->setXY(-82,36); // lon, lat
>>
>> // Run a point query on the line object layer; layer must have a class
>> with a LAYER TEMPLATE value
>> // The third argument is the buffer tolerance.  Default unit is pixels?
>>   Must figure out how to make miles or km.
>> if ($my_layer->queryByPoint($my_point,MS_SINGLE,1)==MS_SUCCESS){
>>
>>          $my_result = $my_layer->getResult(0);  // Get the result
>>          $my_layer =
>> $my_layer->getShape($my_result->tileindex,$my_result->shapeindex);  //
>> Get the shape
>>
>> }
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