[OpenLayers-Users] Split a line feature with a MultiLineString

[sendeman]

Hi All,

I have an OpenLayers application that in which I have an XYZ-subsurface
model residing in a MySQL database table. The model has a record for each
voxel that has an X, Y and Z value and a value that indicates the soil type
(e.g. 1 for clay, 2 for loam, etcetera).

Using php, jQuery and OpenLayers I am able to retrieve all the relevant
records for a location when a user clicks on the map. The php script returns
a column with all the soillayers.

Now what I also want to do is create the possibility for a user to draw a
section line on the map and then get a vertical cross-section from the
XYZ-model. To do this I mean to let the user draw a line and using the
featureadded event I want to split the drawn line at every intersection with
the grid of the XYZ model.

I thought this should be possible with the 
http://dev.openlayers.org/docs/files/OpenLayers/Geometry/MultiLineString-js.html#OpenLayers.Geometry.MultiLineString.split
split function for the MultiLineString . I built a WKT-string to create a
MultiLineString for the grid. I have added the cell size as a variable to
the script, so it will be reusable for models with different cell sizes. I
want to intersect the drawn line with the created grid. This doesn't work. I
get an error in Firebug:

SectionGridFeature.split is not a function
http://localhost/geoviewer/javascript/crosssection.js
Line 75 ed. This would be the line stating:
'SectionGridFeature.split(varSections.features[0]);'


For the script I made, see below. This doesn't include the entire openlayers
script I built, but just the section I'm using for the creation of the
cross-section.

My question is: how can I make the split function work? I fear something may
be wrong with the MultiLineString...

Best regards,
Martijn Senden.


// JavaScript Document for drawing profile lines that are used for drawing
// cross-sections through the Rockworks XYZ-model in the MWH Geoviewer
// V. 1.0 By Martijn Senden, MWH B.V., The Netherlands

// Project parameters
var CellSize = 10; //Size of the grid cells in the XYZ-model 

//  Stylemap for Cross-section line
function initCrossSection() {
  var StyleCustomCrossSectionLine = new OpenLayers.StyleMap({
    "default": new OpenLayers.Style({
                strokeColor: "#ffff00",
                strokeWidth: 2.5
              })
  });
  var StyleCustomGrid = new OpenLayers.StyleMap({
    "default": new OpenLayers.Style({
                strokeColor: "#ffff00",
                fillColor: "#ffbb00",
                strokeWidth: 2.5
              })
  });

// Addition of cross-section layer to map and enter drawing mode 
  var varSections = new OpenLayers.Layer.Vector("Section Line", {
  visibility: true, styleMap: StyleCustomCrossSectionLine});
  map.addLayer(varSections);
  var varSection = new OpenLayers.Control.DrawFeature(
    varSections,
    OpenLayers.Handler.Path,
    {displayClass: 'olControlDrawFeaturePolygon'}
  );
  varSections.events.on({
    //Delete previous line before new feature is added
    "beforefeatureadded": function(evt) {
      var i, len, toDestroy = []
      for(i=0,len=varSections.features.length; i<len; i++) {
        if(varSections.features[i] != evt.feature) {
          toDestroy.push(varSections.features[i]);
        }
      }
      varSections.destroyFeatures(toDestroy);   
    },
    //When new feature is added:
    "featureadded": function(evt) {
      
      //Get Xmin, Xmax, Ymin and Ymax for the new grid used for intersection
      var SectionBounds =
varSections.features[0].geometry.getBounds().clone();
      var vXmin = RoundToGrid(SectionBounds.left,CellSize,"Up");
      var vXmax = RoundToGrid(SectionBounds.right,CellSize,"Down");
      var vYmin = RoundToGrid(SectionBounds.bottom,CellSize,"Up");
      var vYmax = RoundToGrid(SectionBounds.top,CellSize,"Down");

      //Create intersection polygon grid
      var varSectionGrid = new OpenLayers.Layer.Vector("Section Gridpunten",
{visibility: true, styleMap: StyleCustomGrid});
      parser = new OpenLayers.Format.WKT();

      var wkt = " MULTILINESTRING(";
      
      //Draw vertical lines
      for (y = vYmin; y < vYmax; y = y + CellSize) {
        wkt = wkt+"("+vXmin+" "+y+")("+vXmax+" "+y+")";
      }
      //Draw horizontal lines
      for (x = vXmin; x < vXmax; x = x + CellSize) {
        wkt = wkt+"("+x+" "+vYmin+")("+x+" "+vYmax+")";
      }
      var SectionGridGeometry = parser.read(wkt);
      var SectionGridFeature = new
OpenLayers.Feature.Vector(SectionGridGeometry);
      varSectionGrid.addFeatures(SectionGridFeature);

      //Split the Section line with the temporary grid      
      SectionGridFeature.split(varSections.features[0]);
      varSectionGrid.features[0].geometry.split(varSections.features[0]);

      //Construct Json-string from the coordinates of the vertices of the
drawn section line  
      varSectionCoords = '{';
      for (var i = 0; i < varSections.features[0].geometry.components.length
- 1; i++) {
        varSectionCoords = varSectionCoords + '"point' + '":{"x":"' +
varSections.features[0].geometry.components[i].x + '","y":"' +
varSections.features[0].geometry.components[i].y + '"},';
      }
      varSectionCoords = varSectionCoords + '"point' + '":{"x":"' +
varSections.features[0].geometry.components[varSections.features[0].geometry.components.length
- 1].x + '","y":"' +
varSections.features[0].geometry.components[varSections.features[0].geometry.components.length
- 1].y + '"}}';      
    }
  });
  map.addControl(varSection);
  varSection.activate();
}

function RoundToGrid(Value, GridResolution, Type) {
  switch (Type) {
    case "Up":
      return Math.ceil(Value / GridResolution)*GridResolution;
      break;
    case "Down":
      return Math.floor(Value / GridResolution)*GridResolution;
      break;
    case "Round":
      return Math.round(Value / GridResolution)*GridResolution;
      break;
  }
}

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