How to search with filleting custom taxonomy and custom fields

I wanna explain about my search box, actually what i want to make.

Ive a search input and few check boxes to filter the search result.

i need to search like this :

[Country1] AND ( [venue1] OR [venue2] ) AND ( [category1] OR [category2] ) AND [topic1] AND ( BETWEEN $datefrom & $datetill )

Markup :

<form role="search" method="GET" id="searchform" action="<?php echo home_url( '/' ); ?>" >

<input class="form-control" type="text" name="s" id="s" <?php if(is_search()) { ?>value="<?php the_search_query(); ?>" <?php } else { ?>value="Enter keywords &hellip;" onfocus="if(this.value==this.defaultValue)this.value='';" onblur="if(this.value=='')this.value=this.defaultValue;"<?php } ?> /><br />

<button class="btn btn-primary" type="submit" id="searchsubmit" value="Search" > Search </button>


    <h4>Countries</h4>
        <input name="location" value="Country1" type="radio" >Country1</label>
        <input name="location" value="Country2" type="radio" >Country2</label>
        <input name="location" value="Country3" type="radio" >Country3</label>
        <input name="location" value="Country4" type="radio" >Country4</label>

    <h4>Venues</h4>
        <input name="location" value="venue1" type="checkbox" >venue1</label>
        <input name="location" value="venue2" type="checkbox" >venue2</label>
        <input name="location" value="venue3" type="checkbox" >venue3</label>
        <input name="location" value="venue4" type="checkbox" >venue4</label>

    <h4>Custom taxonomy/Category</h4>
        <?php       
            $categories = get_terms( 'eventcategory', array(
                        'orderby'    => 'title',
                        'hide_empty' => 0,
            ) );

            foreach ($categories as $va) {
                $cat_code = "<label>";
                $cat_code .= "<input name='category_name' type='checkbox' value='";
                $cat_code .= $va->name;
                $cat_code .= "' /> ";
                $cat_code .= $va->name;
                $cat_code .= "</label> ";
                echo $cat_code;
            }
        ?>

    <h4>Topic</h4>
        <input name="location" value="Topic1" type="radio" >Topic1</label>
        <input name="location" value="Topic2" type="radio" >Topic2</label>
        <input name="location" value="Topic3" type="radio" >Topic3</label>
        <input name="location" value="Topic4" type="radio" >Topic4</label>


    <h4>Date</h4>
        <input name="datefrom" id="datepicker1" type="text" class="form-control" /> 
        <input name="datetill" id="datepicker2" type="text" class="form-control" />
</form>

functions.php

function search_filter($query) {
if ( !is_admin() && $query->is_main_query() ) {
    if ( $query->is_search ) {

        $searchfield = $_GET['s'];
        $country = $_GET['location'];

        $venue_s = $_GET['venue'];
        $industry = $_GET['industry'];
        $datefrom = $_GET['datefrom'];
        $datetill = $_GET['datetill'];
        $filter_cat = $_POST['category_name'];

        $rel = 'OR';

        $metaQuery = array( 'relation' => $rel,
            array( 'key' => 'location', 'value' => $country, 'compare' => 'IN' ),
            array( 'key' => 'venue', 'value' => $venue_s, 'compare' => '==' ),
            array( 'key' => 'industry', 'value' => $industry, 'compare' => '==' ),
            array( 'key' => 'datefrom', 'value' => array($datefrom, $datetill), 'compare' => 'BETWEEN' )
        );
        $query->set( 'meta_query' , $metaQuery );

    }   
}   
}
add_action('pre_get_posts','search_filter');

My Problem is it so weird, i don't understand