How to set LIBUSB_INCLUDE_DIR

I am trying to cross compile libftdi for a hand. When I start Cmake, I get:

CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake files:
LIBUSB_INCLUDE_DIR (ADVANCED)

I understand that LIBUSB_INCLUDE_DIR must be installed in FindUSB1.cmake found in the libftdi root directory. However, I do not know how to get FindUSB1.cmake to find libusb, which I compiled and put in / opt / lib. This is the default file:

# - Try to find the freetype library
# Once done this defines
#
#  LIBUSB_FOUND - system has libusb
#  LIBUSB_INCLUDE_DIR - the libusb include directory
#  LIBUSB_LIBRARIES - Link these to use libusb

# Copyright (c) 2006, 2008  Laurent Montel, <montel@kde.org>
#
# Redistribution and use is allowed according to the terms of the BSD license.
# For details see the accompanying COPYING-CMAKE-SCRIPTS file.


if (LIBUSB_INCLUDE_DIR AND LIBUSB_LIBRARIES)

  # in cache already
  set(LIBUSB_FOUND TRUE)

else (LIBUSB_INCLUDE_DIR AND LIBUSB_LIBRARIES)
  IF (NOT WIN32)
    # use pkg-config to get the directories and then use these values
    # in the FIND_PATH() and FIND_LIBRARY() calls

    find_package(PkgConfig)
    pkg_check_modules(PC_LIBUSB libusb-1.0)
  ENDIF(NOT WIN32)

  FIND_PATH(LIBUSB_INCLUDE_DIR libusb.h
    PATHS ${PC_LIBUSB_INCLUDEDIR} ${PC_LIBUSB_INCLUDE_DIRS})

  FIND_LIBRARY(LIBUSB_LIBRARIES NAMES usb-1.0
    PATHS ${PC_LIBUSB_LIBDIR} ${PC_LIBUSB_LIBRARY_DIRS})

  include(FindPackageHandleStandardArgs)
  FIND_PACKAGE_HANDLE_STANDARD_ARGS(LIBUSB DEFAULT_MSG LIBUSB_LIBRARIES LIBUSB_INCLUDE_DIR)

  MARK_AS_ADVANCED(LIBUSB_INCLUDE_DIR LIBUSB_LIBRARIES)

endif (LIBUSB_INCLUDE_DIR AND LIBUSB_LIBRARIES)

There is a pkconfig directory in / opt / lib. There is a libusb-1.0.pc file in this directory, which I think may have something to do with the problem. So, how do I get Cmake to find / opt / lib / libsub-1.0?