Please keep in mind that it's optional to set the variant and size for the following ones, as this size (24) and style (filled) combination is defined as the default.
In case that you'll need another default in your project, you could overwrite the defaults by modifying the $icon-size and $icon-style SCSS variables.

• • SCSS: @include icon(glyph(gps)) or @include icon(glyph(gps), 24, "filled")
  • HTML: data-icon="gps" or data-icon="gps" data-icon-variant="24-filled"
• • SCSS: @include icon(glyph(gps-north)) or @include icon(glyph(gps-north), 24, "filled")
  • HTML: data-icon="gps-north" or data-icon="gps-north" data-icon-variant="24-filled"