How to Use XSLT to Replace Coordinate Separator With List of Tuples?

Question

I have a space-separated list of coordinate tuples, with arbitrarily many tuples. Each tuple consists of a space-separated list of 2-dimensional coordinates. E.g. "1.1 2.8 1.2 2.9" represents a line from POINT(1.1 2.8) to POINT(1.2 2.9). I need this to instead be "1.1,2.8 1.2,2.9". How would I use XSLT to perform the replacement of space-to-comma between pairs of numbers? I have the "string(gml:LinearRing/gml:posList)".

This is being used on a Java Web Service that spits out GML 3.1.1 features with geometries. The service supports optional KML output, by using XSLT to transform the GML document into a KML document (at least, the chunks deemed "important"). I am locked into XSLT 1.0, so regex from XSLT 2.0 is not an option.

I am aware that GML uses lat/lon while KML uses lon/lat. That's being handled before XSLT, though it would be nice to have that also done with XSLT.

---

Thank you for your solution, Dimitre. I modified it a little to fit my needs, so I'll include that here in case it helps anyone else. It performs recursion through the coordinate list, assuming 2-dimensional tuples.

This performs two functions: axis swapping (lat/lon for lon/lat, per GML and KML specs) and changing the coordinate separator within each tuple from space ' ' to comma ','.

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:gml="http://www.opengis.net/gml" exclude-result-prefixes="gml">
   <xsl:output method="xml" encoding="UTF-8" indent="yes" />

   <!-- other portions omitted -->

   <xsl:template match="gml:pos">
      <xsl:call-template name="coordinateSequence">
         <xsl:with-param name="coords" select="normalize-space(string(.))" />
      </xsl:call-template>
   </xsl:template>

   <xsl:template match="gml:posList">
      <xsl:call-template name="coordinateSequence">
         <xsl:with-param name="coords" select="normalize-space(string(.))" />
      </xsl:call-template>
   </xsl:template>

   <xsl:template name="coordinateSequence">
      <xsl:param name="coords" />
      <xsl:if test="string-length($coords) > 0">
         <xsl:variable name="lat" select="substring-before($coords, ' ')" />
         <xsl:variable name="lon">
            <xsl:value-of select="substring-before(substring-after($coords, ' '), ' ')" />
            <xsl:if test="string-length(substring-before(substring-after($coords, ' '), ' ')) = 0">
               <xsl:value-of select="substring-after($coords, ' ')" />
            </xsl:if>
         </xsl:variable>
         <xsl:variable name="remainder" select="substring-after(substring-after($coords, ' '), ' ')" />

         <xsl:value-of select="concat($lon, ',', $lat)" />
         <xsl:if test="string-length($remainder) > 0">
            <xsl:value-of select="' '" />
            <xsl:call-template name="coordinateSequence">
               <xsl:with-param name="coords" select="$remainder" />
            </xsl:call-template>
         </xsl:if>
      </xsl:if>
   </xsl:template>

</xsl:stylesheet>

Answer 1

This transformation (also shows the intermediary steps):

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output method="text"/>

 <xsl:template match="/*">
  <xsl:variable name="vNorm" select="normalize-space()"/>
  <xsl:variable name="vP1" select=
  "concat(substring-before(., ' '), ',',
          substring-before(substring-after($vNorm, ' '),' ')
          )"/>

  <xsl:variable name="vPart2" select="substring-after(substring-after($vNorm,' '),' ')"/>

  <xsl:variable name="vP2" select=
  "concat(substring-before($vPart2, ' '), ',',
          substring-after($vPart2, ' ')
          )"/>


  <xsl:value-of select="$vP1"/>
==========
  <xsl:value-of select="$vP2"/>
==========
  <xsl:value-of select="concat($vP1, ' ', $vP2)"/>
 </xsl:template>
</xsl:stylesheet>

when applied on this XML document:

<t>1.1 2.8 1.2 2.9</t>

produces the wanted, correct result (the last line):

1.1,2.8
==========
  1.2,2.9
==========
  1.1,2.8 1.2,2.9

For convenience, this code can be placed in to a named template to be called for each wanted Line:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:output method="text"/>

 <xsl:template match="/*">
  <xsl:call-template name="convertLine"/>
 </xsl:template>

 <xsl:template name="convertLine">
  <xsl:param name="pStr" select="."/>

  <xsl:variable name="vNorm" select="normalize-space($pStr)"/>
  <xsl:variable name="vP1" select=
  "concat(substring-before($pStr, ' '), ',',
          substring-before(substring-after($vNorm, ' '),' ')
          )"/>

  <xsl:variable name="vPart2" select="substring-after(substring-after($vNorm,' '),' ')"/>

  <xsl:variable name="vP2" select=
  "concat(substring-before($vPart2, ' '), ',',
          substring-after($vPart2, ' ')
          )"/>


  <xsl:value-of select="concat($vP1, ' ', $vP2)"/>
 </xsl:template>
</xsl:stylesheet>

Answer 2

<xsl:for-each select="tokenize($in, ' ')">
  <xsl:value-of select="concat($t, if (position() mod 2) = 0 then ' ' else ',')"/>
</xsl:for-each>