Hi list members,

I'm relatively new to mkgmap.  I have a question about displaying shields on highways.  Table 4.4 in the Conversion Style Manual shows highway shields displaying numbers only, which is what I would like to achieve.  In Table 4.3 (the list of substitution filters), the description for the highway-symbol filter says that the filer "Prepares the value as a highway reference such as 'A21' 'I-80' and so on.  A code is added to the front of the string so that a highway shield is displayed, spaces are removed and the text is truncated so as not to overflow the symbol."  The description does not explain (from what I can tell) how to remove the alphabetic characters, leaving only the numbers.  I've tried several possibilities of the filter without success.  Where I live, there's a motorway called Interstate 70 which is labeled "I70" in OSM.  I would like to create shields with only the number in the shields, similar to the example in Table 4.4.  How do I do this?

Mark