How can i create a GeoTiff with geotiffwrite without EPSG code?

Hi,

when I'm using the function geotiffwrite I have to define a epsg code for the georeferencing of the output GeoTiff ('CoordRefSysCode'). The problem is that I'm working in local coordinate system, for which no EPSG code exists in 'matlabroot/toolbox/map/mapproj/projdata/epsg_csv/pcs.csv'. Is there any way to omit the 'CoordRefSysCode' parameter for the creation of the GeoTiff?

Thanks for your help.

p.s.: 32767 is the epsg code for a user-defined projection (according to http://www.remotesensing.org/geotiff/spec/geotiff6.html#6.3.3.1). That doesn't work either.