Re: XSLT code that implements the Point-in-a-Polygon

Just looking at the code, wondering why it's using xsl:choose: could you not
do all of it in a single XPath expression, even in XSLT 2?

Cheers,

E.

--
Eliot Kimber
http://contrext.com


o;?On 12/10/20, 1:22 PM, "Roger L Costello costello@xxxxxxxxx"
<xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote:

    Hi Folks,

    I implemented XSLT code to determine if a point p is inside or outside a
polygon. See below. Admittedly, the tests that I've done thus far are really
simple. See the template rule. I would appreciate it if you see a bug in the
code or see where the code can be improved, you would let me know please.
/Roger

    <?xml version="1.0" encoding="UTF-8"?>
    <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
        xmlns:xs="http://www.w3.org/2001/XMLSchema"
        xmlns:f="function"
        exclude-result-prefixes="#all"
        version="2.0">

        <xsl:output method="text" />

        <!--
            Given a point p, does p reside in the polygon with N edges?
            This program solves the Point-in-a-Polygon problem.
        -->

        <!--
            The following code implements in XSLT the C code
            shown in Solution 1 at this URL:
            http://www.eecs.umich.edu/courses/eecs380/HANDOUTS/PROJ2/InsidePo
ly.html
        -->
        <xsl:function name="f:iterate-Over-All-Polygons" as="xs:string">
            <xsl:param name="polygon" as="xs:string+" />
            <xsl:param name="N" as="xs:integer" />
            <xsl:param name="p" as="xs:string" />
            <xsl:param name="counter" as="xs:integer" />
            <xsl:param name="p1" as="xs:string" />
            <xsl:param name="i" as="xs:integer" />

            <xsl:variable name="p_x" select="xs:double(tokenize($p, ' ')[1])"
as="xs:double" />
            <xsl:variable name="p_y" select="xs:double(tokenize($p, ' ')[2])"
as="xs:double" />


            <xsl:variable name="p1_x" select="xs:double(tokenize($p1, '
')[1])" as="xs:double" />
            <xsl:variable name="p1_y" select="xs:double(tokenize($p1, '
')[2])" as="xs:double" />

            <xsl:choose>
                <xsl:when test="$i le $N">
                    <!-- p2 = polygon[i % N] -->
                    <xsl:variable name="p2" select="$polygon[($i mod $N) + 1]"
as="xs:string"/>
                    <xsl:variable name="p2_x" select="xs:double(tokenize($p2,
' ')[1])" as="xs:double" />
                    <xsl:variable name="p2_y" select="xs:double(tokenize($p2,
' ')[2])" as="xs:double" />
                    <!-- if (p.y > MIN(p1.y,p2.y)) -->
                    <xsl:choose>
                        <xsl:when test="$p_y gt min(($p1_y, $p2_y))">
                            <!-- if (p.y <= MAX(p1.y,p2.y)) -->
                            <xsl:choose>
                                <xsl:when test="$p_y le max(($p1_y, $p2_y))">
                                    <!-- if (p.x <= MAX(p1.x,p2.x)) -->
                                    <xsl:choose>
                                        <xsl:when test="$p_x le max(($p1_x,
$p2_x))">
                                            <!-- if (p1.y != p2.y) -->
                                            <xsl:choose>
                                                <xsl:when test="$p1_y ne
$p2_y">
                                                    <!-- xinters =
(p.y-p1.y)*(p2.x-p1.x)/(p2.y-p1.y)+p1.x -->
                                                    <xsl:variable
name="xinters" select="($p_y - $p1_y)*($p2_x - $p1_x) div ($p2_y - $p1_y) +
$p1_x" as="xs:double" />
                                                    <!-- if (p1.x == p2.x ||
p.x <= xinters) -->
                                                    <xsl:choose>
                                                        <xsl:when test="$p1_x
eq $p2_x or $p_x le $xinters">
                                                            <!-- counter++
-->
                                                            <!-- p1 = p2 -->
                                                            <xsl:sequence
select="f:iterate-Over-All-Polygons($polygon, $N, $p, $counter + 1, $p2, $i +
1)" />
                                                        </xsl:when>
                                                        <xsl:otherwise>
                                                            <!-- p1 = p2 -->
                                                            <xsl:sequence
select="f:iterate-Over-All-Polygons($polygon, $N, $p, $counter, $p2, $i + 1)"
/>
                                                        </xsl:otherwise>
                                                    </xsl:choose>
                                                </xsl:when>
                                                <xsl:otherwise>
                                                    <!-- p1 = p2 -->
                                                    <xsl:sequence
select="f:iterate-Over-All-Polygons($polygon, $N, $p, $counter, $p2, $i + 1)"
/>
                                                </xsl:otherwise>
                                            </xsl:choose>
                                        </xsl:when>
                                        <xsl:otherwise>
                                            <!-- p1 = p2 -->
                                            <xsl:sequence
select="f:iterate-Over-All-Polygons($polygon, $N, $p, $counter, $p2, $i + 1)"
/>
                                        </xsl:otherwise>
                                    </xsl:choose>
                                </xsl:when>
                                <xsl:otherwise>
                                    <!-- p1 = p2 -->
                                    <xsl:sequence
select="f:iterate-Over-All-Polygons($polygon, $N, $p, $counter, $p2, $i + 1)"
/>
                                </xsl:otherwise>
                            </xsl:choose>
                        </xsl:when>
                        <xsl:otherwise>
                            <!-- p1 = p2 -->
                            <xsl:sequence
select="f:iterate-Over-All-Polygons($polygon, $N, $p, $counter, $p2, $i + 1)"
/>
                        </xsl:otherwise>
                    </xsl:choose>
                </xsl:when>
                <xsl:otherwise>
                    <xsl:message>Number of times a horizontal ray eminating
from p to the right intersects the line segments making up the polygon =
<xsl:value-of select="$counter" /></xsl:message>
                    <!--
                        if (counter % 2 == 0)
                            return(OUTSIDE);
                        else
                            return(INSIDE)
                    -->
                    <xsl:choose>
                        <xsl:when test="($counter mod 2) eq
0"><xsl:text>OUTSIDE</xsl:text></xsl:when>
                        <xsl:otherwise><xsl:text>INSIDE</xsl:text></xsl:other
wise>
                    </xsl:choose>
                </xsl:otherwise>
            </xsl:choose>

        </xsl:function>

        <xsl:function name="f:InsidePolygon" as="xs:string">
            <xsl:param name="polygon" as="xs:string+" />
            <xsl:param name="N" as="xs:integer" />
            <xsl:param name="p" as="xs:string" />  <!-- p1 = polygon[1] -->

            <xsl:variable name="counter" select="0" as="xs:integer" />
            <xsl:variable name="p1" select="$polygon[1]" as="xs:string" />
            <xsl:variable name="i" select="1" as="xs:integer" />

            <xsl:sequence select="f:iterate-Over-All-Polygons($polygon, $N,
$p, $counter, $p1, $i)" />

        </xsl:function>

        <xsl:template match="/">
            <xsl:variable name="polygon" as="xs:string+">
                <xsl:sequence select="'0 0'" />
                <xsl:sequence select="'4 0'" />
                <xsl:sequence select="'4 4'" />
                <xsl:sequence select="'0 4'" />
                <xsl:sequence select="'0 0'" />
            </xsl:variable>
            <xsl:variable name="N" select="5" as="xs:integer" />

            <xsl:variable name="p" select="'1 1'" as="xs:string" />
            <xsl:sequence select="f:InsidePolygon($polygon,$N, $p)" />

            <xsl:variable name="p" select="'-1 1'" as="xs:string" />
            <xsl:sequence select="f:InsidePolygon($polygon,$N, $p)" />

            <xsl:variable name="p" select="'0 0'" as="xs:string" />
            <xsl:sequence select="f:InsidePolygon($polygon,$N, $p)" />

            <xsl:variable name="p" select="'0.2 0.5'" as="xs:string" />
            <xsl:sequence select="f:InsidePolygon($polygon,$N, $p)" />

        </xsl:template>

    </xsl:stylesheet>