[FEATURE][processing] Algorithm to find an unknown layer's projection

If you have a layer with an unknown CRS, this algorithm gives a list
of possible candidate CRSes which the layer could be in.

It allows users to set the area (and corresponding CRS) which they know
the layer should be located near. The algorithm then tests every CRS
in the database to see what candidate CRSes would cause the layer
to be located at that preset area.

It's much faster than it sounds!! (just a couple of seconds)

Sponsored by SMEC/Surbana Jurong

python/plugins/processing/algs/help/qgis.yaml

@@ -200,6 +200,13 @@ qgis:extractspecificnodes: >
 qgis:fieldcalculator: >
   This algorithm computes a new vector layer with the same features of the input layer, but with an additional attribute. The values of this new attribute are computed from each feature using a mathematical formula, based on te properties and attributes of the feature.
 
+qgis:findprojection: >
+  This algorithm allows creation of a shortlist of possible candidate coordinate reference systems for a layer with an unknown projection.
+
+  The expected area which the layer should reside in must be specified via the target area parameter. Additionally, the coordinate reference system for this target area must also be set.
+
+  The algorithm operates by testing the layer's extent in every known reference system and listing any in which the bounds would fall near the target area if the layer was in this projection.
+
 qgis:fixeddistancebuffer: >
   This algorithm computes a buffer area for all the features in an input layer, using a fixed distance.
 

python/plugins/processing/algs/qgis/FindProjection.py

@@ -0,0 +1,116 @@
+# -*- coding: utf-8 -*-
+
+"""
+***************************************************************************
+    FindProjection.py
+    -----------------
+    Date                 : February 2017
+    Copyright            : (C) 2017 by Nyall Dawson
+    Email                : nyall dot dawson at gmail dot com
+***************************************************************************
+*                                                                         *
+*   This program is free software; you can redistribute it and/or modify  *
+*   it under the terms of the GNU General Public License as published by  *
+*   the Free Software Foundation; either version 2 of the License, or     *
+*   (at your option) any later version.                                   *
+*                                                                         *
+***************************************************************************
+"""
+
+__author__ = 'Nyall Dawson'
+__date__ = 'February 2017'
+__copyright__ = '(C) 2017, Nyall Dawson'
+
+# This will get replaced with a git SHA1 when you do a git archive
+
+__revision__ = '$Format:%H$'
+
+import os
+import codecs
+
+from qgis.core import (QgsGeometry,
+                       QgsRectangle,
+                       QgsCoordinateReferenceSystem,
+                       QgsCoordinateTransform)
+
+from processing.core.GeoAlgorithm import GeoAlgorithm
+from processing.core.parameters import ParameterVector
+from processing.core.parameters import ParameterCrs
+from processing.core.parameters import ParameterExtent
+from processing.core.outputs import OutputHTML
+from processing.tools import dataobjects
+
+
+pluginPath = os.path.split(os.path.split(os.path.dirname(__file__))[0])[0]
+
+
+class FindProjection(GeoAlgorithm):
+
+    INPUT_LAYER = 'INPUT_LAYER'
+    TARGET_AREA = 'TARGET_AREA'
+    TARGET_AREA_CRS = 'TARGET_AREA_CRS'
+    OUTPUT_HTML_FILE = 'OUTPUT_HTML_FILE'
+
+    def defineCharacteristics(self):
+        self.name, self.i18n_name = self.trAlgorithm('Find projection')
+        self.group, self.i18n_group = self.trAlgorithm('Vector general tools')
+        self.tags = self.tr('crs,srs,coordinate,reference,system,guess,estimate,finder,determine')
+
+        self.addParameter(ParameterVector(self.INPUT_LAYER,
+                                          self.tr('Input layer')))
+        extent_parameter = ParameterExtent(self.TARGET_AREA,
+                                           self.tr('Target area for layer'),
+                                           self.INPUT_LAYER)
+        extent_parameter.skip_crs_check = True
+        self.addParameter(extent_parameter)
+        self.addParameter(ParameterCrs(self.TARGET_AREA_CRS, 'Target area CRS'))
+
+        self.addOutput(OutputHTML(self.OUTPUT_HTML_FILE,
+                                  self.tr('Candidates')))
+
+    def processAlgorithm(self, feedback):
+        layer = dataobjects.getObjectFromUri(
+            self.getParameterValue(self.INPUT_LAYER))
+
+        extent = self.getParameterValue(self.TARGET_AREA).split(',')
+        target_crs = QgsCoordinateReferenceSystem(self.getParameterValue(self.TARGET_AREA_CRS))
+
+        target_geom = QgsGeometry.fromRect(QgsRectangle(float(extent[0]), float(extent[2]),
+                                                        float(extent[1]), float(extent[3])))
+
+        output_file = self.getOutputValue(self.OUTPUT_HTML_FILE)
+
+        # make intersection tests nice and fast
+        engine = QgsGeometry.createGeometryEngine(target_geom.geometry())
+        engine.prepareGeometry()
+
+        layer_bounds = QgsGeometry.fromRect(layer.extent())
+
+        results = []
+
+        for srs_id in QgsCoordinateReferenceSystem.validSrsIds():
+            candidate_crs = QgsCoordinateReferenceSystem.fromSrsId(srs_id)
+            if not candidate_crs.isValid():
+                continue
+
+            transform_candidate = QgsCoordinateTransform(candidate_crs, target_crs)
+            transformed_bounds = QgsGeometry(layer_bounds)
+            try:
+                if not transformed_bounds.transform(transform_candidate) == 0:
+                    continue
+            except:
+                continue
+
+            if engine.intersects(transformed_bounds.geometry()):
+                results.append(candidate_crs.authid())
+
+        self.createHTML(output_file, results)
+
+    def createHTML(self, outputFile, candidates):
+        with codecs.open(outputFile, 'w', encoding='utf-8') as f:
+            f.write('<html><head>\n')
+            f.write('<meta http-equiv="Content-Type" content="text/html; \
+                    charset=utf-8" /></head><body>\n')
+            for c in candidates:
+                f.write('<p>' + c + '</p>\n')
+            f.write('</body></html>\n')

python/plugins/processing/algs/qgis/QGISAlgorithmProvider.py

@@ -186,6 +186,7 @@
 from .Polygonize import Polygonize
 from .FixGeometry import FixGeometry
 from .ExecuteSQL import ExecuteSQL
+from .FindProjection import FindProjection
 
 pluginPath = os.path.normpath(os.path.join(
     os.path.split(os.path.dirname(__file__))[0], os.pardir))
@@ -255,7 +256,7 @@ def __init__(self):
                         ShortestPathPointToPoint(), ShortestPathPointToLayer(),
                         ShortestPathLayerToPoint(), ServiceAreaFromPoint(),
                         ServiceAreaFromLayer(), TruncateTable(), Polygonize(),
-                        FixGeometry(), ExecuteSQL()
+                        FixGeometry(), ExecuteSQL(), FindProjection()
                         ]
 
         if hasMatplotlib:

python/plugins/processing/tests/testdata/custom/find_projection.gfs

@@ -0,0 +1,16 @@
+<GMLFeatureClassList>
+  <GMLFeatureClass>
+    <Name>find_projection</Name>
+    <ElementPath>find_projection</ElementPath>
+    <!--POINT-->
+    <GeometryType>1</GeometryType>
+    <SRSName>EPSG:28356</SRSName>
+    <DatasetSpecificInfo>
+      <FeatureCount>4</FeatureCount>
+      <ExtentXMin>326064.87345</ExtentXMin>
+      <ExtentXMax>328710.85361</ExtentXMax>
+      <ExtentYMin>6245538.80829</ExtentYMin>
+      <ExtentYMax>6247808.84283</ExtentYMax>
+    </DatasetSpecificInfo>
+  </GMLFeatureClass>
+</GMLFeatureClassList>

python/plugins/processing/tests/testdata/custom/find_projection.gml

@@ -0,0 +1,34 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ogr:FeatureCollection
+     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+     xsi:schemaLocation=""
+     xmlns:ogr="http://ogr.maptools.org/"
+     xmlns:gml="http://www.opengis.net/gml">
+  <gml:boundedBy>
+    <gml:Box>
+      <gml:coord><gml:X>326064.8734538725</gml:X><gml:Y>6245538.808291084</gml:Y></gml:coord>
+      <gml:coord><gml:X>328710.8536064086</gml:X><gml:Y>6247808.842832778</gml:Y></gml:coord>
+    </gml:Box>
+  </gml:boundedBy>
+
+  <gml:featureMember>
+    <ogr:find_projection fid="find_projection.0">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:28356"><gml:coordinates>326597.10210384,6247528.48897066</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:find_projection>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:find_projection fid="find_projection.1">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:28356"><gml:coordinates>327449.712845641,6246290.065952</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:find_projection>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:find_projection fid="find_projection.2">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:28356"><gml:coordinates>328710.853606409,6247808.84283278</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:find_projection>
+  </gml:featureMember>
+  <gml:featureMember>
+    <ogr:find_projection fid="find_projection.3">
+      <ogr:geometryProperty><gml:Point srsName="EPSG:28356"><gml:coordinates>326064.873453873,6245538.80829108</gml:coordinates></gml:Point></ogr:geometryProperty>
+    </ogr:find_projection>
+  </gml:featureMember>
+</ogr:FeatureCollection>

python/plugins/processing/tests/testdata/expected/find_projection.html

@@ -0,0 +1,11 @@
+<html><head>
+<meta http-equiv="Content-Type" content="text/html;                     charset=utf-8" /></head><body>
+<p>EPSG:20256</p>
+<p>EPSG:20356</p>
+<p>EPSG:28356</p>
+<p>EPSG:32356</p>
+<p>EPSG:32556</p>
+<p>EPSG:32756</p>
+<p>IGNF:UTM56SW84</p>
+<p>EPSG:5552</p>
+</body></html>

python/plugins/processing/tests/testdata/qgis_algorithm_tests.yaml

@@ -2347,3 +2347,17 @@ tests:
       OUTPUT:
         name: expected/voronoi_buffer.gml
         type: vector
+
+  - algorithm: qgis:findprojection
+    name: Find projection
+    params:
+      INPUT_LAYER:
+        name: custom/find_projection.gml
+        type: vector
+      TARGET_AREA: 151.1198,151.1368,-33.9118,-33.9003
+      TARGET_AREA_CRS: EPSG:4326
+    results:
+      OUTPUT_HTML_FILE:
+        name: expected/find_projection.html
+        type: file
+