Custom controller getproducts sort by position

[kris12]

        $products_partial = Product::getProducts($this->context->language->id, 0, 0, 'id_product', 'asc');
        $products = Product::getProductsProperties($this->context->language->id, $products_partial);
        $this->addColorsToProductList($products);

Hello, i'm having a hard time figuring out how to make the sort by position work in a custom controller that list all products. i can do sort by id, date, name,... but not the position which is linked to the category table. Anyone have an idea how to achieve this ?