Get map legend while using Transformation Functions in SLD style

Question

In my project I have a SLD style which contain Transformation function. The SLD style is looks like this:

<PointSymbolizer>
    <Fill>
        <CssParameter name="fill">
            <ogc:Function name="Recode">
                <ogc:PropertyName>nature</ogc:PropertyName>
                <ogc:Literal>Commercial</ogc:Literal>
                <ogc:Literal>#ba0d5a</ogc:Literal>
                <ogc:Literal>Residential</ogc:Literal>
                <ogc:Literal>#ba0d5a</ogc:Literal>
            </ogc:Function>
        </CssParameter>
    </Fill>
</PointSymbolizer>

The output of the above looks like this:

So the map is showing properly, but I need to display LegendGraphic also. But requesting LegendGraphic is returning only one symbol

How to get legend based on different attribute?

EDIT :: For your reference this is my complete SLD file

<?xml version="1.0" encoding="UTF-8"?>
<StyledLayerDescriptor version="1.0.0"
    xsi:schemaLocation="http://www.opengis.net/sld StyledLayerDescriptor.xsd"
    xmlns="http://www.opengis.net/sld" xmlns:ogc="http://www.opengis.net/ogc"
    xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <NamedLayer>
        <Name>MadhyamgramGIS:apartment</Name>
        <UserStyle>
            <Title>Dynamic Apartment Layer</Title>
            <Abstract>Dynamic style for point layer</Abstract>
            <FeatureTypeStyle>
                <Rule>
                    <Name>Rule1</Name>
                    <Title>Apartment Layer</Title>
                    <Abstract>Point Rule</Abstract>
                    <PointSymbolizer>
                        <Graphic>
                            <Mark>
                                <WellKnownName>circle</WellKnownName>
                                <Fill>
                                    <CssParameter name="fill">
                                        <ogc:Function name="Recode">
                                            <ogc:PropertyName>nature</ogc:PropertyName>
                                            <ogc:Literal>Commercial</ogc:Literal>
                                            <ogc:Literal>#ba0d5a</ogc:Literal>
                                            <ogc:Literal>Residential</ogc:Literal>
                                            <ogc:Literal>#ba0d5a</ogc:Literal>
                                        </ogc:Function>
                                    </CssParameter>
                                </Fill>
                                <Stroke>
                                    <CssParameter name="stroke">
                                        <ogc:Function name="Recode">
                                            <ogc:PropertyName>nature</ogc:PropertyName>
                                            <ogc:Literal>Commercial</ogc:Literal>
                                            <ogc:Literal>#B0C4DE</ogc:Literal>
                                            <ogc:Literal>Residential</ogc:Literal>
                                            <ogc:Literal>#16e023</ogc:Literal>
                                        </ogc:Function>
                                    </CssParameter>
                                    <CssParameter name="stroke-width">
                                        <ogc:Function name="Recode">
                                            <ogc:PropertyName>nature</ogc:PropertyName>
                                            <ogc:Literal>Commercial</ogc:Literal>
                                            <ogc:Literal>1</ogc:Literal>
                                            <ogc:Literal>Residential</ogc:Literal>
                                            <ogc:Literal>2</ogc:Literal>
                                        </ogc:Function>
                                    </CssParameter>
                                </Stroke>
                            </Mark>
                            <Size>12</Size>
                        </Graphic>
                    </PointSymbolizer>
                </Rule>
            </FeatureTypeStyle>
        </UserStyle>
    </NamedLayer>
</StyledLayerDescriptor>

Answer 1

You have multiple choices. I provide more or less what the URL should look like but they are not working URLs

1. You will need to provide a reference to your SLD like for your getMap call.

   http://localhost:8080/geoserver/wms?REQUEST=GetLegendGraphic&VERSION=1.0.0&FORMAT=image/png&WIDTH=20&HEIGHT=20&LAYER=topp:states&SLD=your_path_to_remote_sld

2. You can provide the SLD body if necessary

   http://localhost:8080/geoserver/wms?REQUEST=GetLegendGraphic&VERSION=1.0.0&FORMAT=image/png&WIDTH=20&HEIGHT=20&LAYER=topp:states&SLD_BODY=your_sld_file_content_inlined

3. You can also provide a style name as long as it's available as an alternate style for your layer internally in your GeoServer admin.

   http://localhost:8080/geoserver/wms?REQUEST=GetLegendGraphic&VERSION=1.0.0&FORMAT=image/png&WIDTH=20&HEIGHT=20&LAYER=topp:states&STYLE=your_style_name_if_available_as_alternate_style_for_the_layer

These informations were deduced from Get Legend Graphic documentation

Answer 2

I tried this problem using different <rule> for different attribute param. Now the SLD file is look like this

<FeatureTypeStyle>
    <Rule>
        <Title>Commercial</Title>
        <ogc:Filter>
            <ogc:PropertyIsEqualTo>
                <ogc:PropertyName>nature</ogc:PropertyName>
                <ogc:Literal>Commercial</ogc:Literal>
            </ogc:PropertyIsEqualTo>
        </ogc:Filter>
        <PointSymbolizer>
            <Graphic>
                <Mark>
                    <WellKnownName>circle</WellKnownName>
                    <Fill>
                        <CssParameter name="fill">#ba0d5a</CssParameter>
                    </Fill>
                    <Stroke>
                        <CssParameter name="stroke">#B0C4DE</CssParameter>
                        <CssParameter name="stroke-width">1</CssParameter>
                    </Stroke>
                </Mark>
                <Size>12</Size>
            </Graphic>
        </PointSymbolizer>
    </Rule>
    <Rule>
       <Title>Residential</Title>
        <ogc:Filter>
            <ogc:PropertyIsEqualTo>
                <ogc:PropertyName>nature</ogc:PropertyName>
                <ogc:Literal>Residential</ogc:Literal>
            </ogc:PropertyIsEqualTo>
        </ogc:Filter>
        <PointSymbolizer>
            <Graphic>
                <Mark>
                    <WellKnownName>triangle</WellKnownName>
                    <Fill>
                        <CssParameter name="fill">#B0C4DE</CssParameter>
                    </Fill>
                    <Stroke>
                        <CssParameter name="stroke">#ba0d5a</CssParameter>
                        <CssParameter name="stroke-width">1</CssParameter>
                    </Stroke>
                </Mark>
                <Size>10</Size>
            </Graphic>
        </PointSymbolizer>
    </Rule>
</FeatureTypeStyle>

Now call to GeoServer using @ThomasG77 answer provide me my requested Legend.

But using rule doesn't display other symbol with doesn't match with the rule, i.e. if their is another nature 'Commercial & Residential' for which i didn't defined any rule that does not display on GetMap