List transformations by suitability

View inQMLC++
View on GitHub
Sample viewer app

Get a list of suitable transformations for projecting a geometry between two spatial references with different horizontal datums.

screenshot

Use case

Transformations (sometimes known as datum or geographic transformations) are used when projecting data from one spatial reference to another when there is a difference in the underlying datum of the spatial references. Transformations can be mathematically defined by specific equations (equation-based transformations), or may rely on external supporting files (grid-based transformations). Choosing the most appropriate transformation for a situation can ensure the best possible accuracy for this operation. Some users familiar with transformations may wish to control which transformation is used in an operation.

How to use the sample

Select a transformation from the list to see the result of projecting the point from EPSG:27700 to EPSG:3857 using that transformation. The result is shown as a red cross; you can visually compare the original blue point with the projected red cross.

If the selected transformation is not usable (has missing grid files) then an error is displayed.

How it works

  1. Pass the input and output spatial references to TransformationCatalog::transformationsBySuitability for transformations based on the map's spatial reference OR additionally provide an extent argument to only return transformations suitable to the extent. This returns a list of ranked transformations.
  2. Use one of the DatumTransformation objects returned to project the input geometry to the output spatial reference.

Relevant API

  • DatumTransformation
  • GeographicTransformation
  • GeographicTransformationStep
  • GeometryEngine
  • GeometryEngine::project
  • TransformationCatalog

About the data

The map starts out zoomed into the grounds of the Royal Observatory, Greenwich. The initial point is in the British National Grid spatial reference, which was created by the United Kingdom Ordnance Survey. The spatial reference after projection is in web mercator.

Additional information

This sample uses a GeographicTransformation, which extends the DatumTransformation class. As of 100.9, ArcGIS Runtime also includes a HorizontalVerticalTransformation, which also extends DatumTransformation. The HorizontalVerticalTransformation class is used to transform coordinates of z-aware geometries between spatial references that have different geographic and/or vertical coordinate systems.

Some transformations aren't available until transformation data is provided.

This sample can be used with or without provisioning projection engine data to your device. If you do not provision data, a limited number of transformations will be available.

This sample uses a GeographicTransformation, which extends the DatumTransformation class. As of 100.9, ArcGIS Runtime also includes a HorizontalVerticalTransformation, which also extends DatumTransformation. The HorizontalVerticalTransformation class is used to transform coordinates of z-aware geometries between spatial references that have different geographic and/or vertical coordinate systems.

To download projection engine data to your device:

  1. Log in to the ArcGIS for Developers site using your Developer account.
  2. In the Dashboard page, click 'Download APIs and SDKs'.
  3. Click the download button next to ArcGIS Runtime Coordinate System Data 100.x to download projection engine data to your computer.
  4. Unzip the downloaded data on your computer.
  5. Create an ~/ArcGIS/Runtime/Data/PEDataRuntime directory on your device and copy the files to this directory.

Tags

datum, geodesy, projection, spatial reference, transformation

Sample Code

ListTransformations.cppListTransformations.cppListTransformations.hListTransformations.qml
Use dark colors for code blocksCopy
                                                                                                                                                                                                   
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
// [WriteFile Name=ListTransformations, Category=Geometry]
// [Legal]
// Copyright 2017 Esri.

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0

// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// [Legal]

#ifdef PCH_BUILD
#include "pch.hpp"
#endif // PCH_BUILD

#include "ListTransformations.h"

#include "Map.h"
#include "MapQuickView.h"
#include "TransformationCatalog.h"
#include "GeometryEngine.h"
#include "GraphicsOverlay.h"
#include "Graphic.h"
#include "Point.h"
#include "SimpleMarkerSymbol.h"
#include "DatumTransformation.h"
#include "GeographicTransformationStep.h"
#include "GeographicTransformation.h"

#include <QDir>
#include <QtCore/qglobal.h>
#include <QUrl>
#include <QVariantMap>

#ifdef Q_OS_IOS
#include <QStandardPaths>
#endif // Q_OS_IOS

using namespace Esri::ArcGISRuntime;

// helper method to get cross platform data path
namespace
{
  QString defaultDataPath()
  {
    QString dataPath;

  #ifdef Q_OS_ANDROID
    dataPath = "/sdcard";
  #elif defined Q_OS_IOS
    dataPath = QStandardPaths::writableLocation(QStandardPaths::DocumentsLocation);
  #else
    dataPath = QDir::homePath();
  #endif

    return dataPath;
  }
} // namespace

ListTransformations::ListTransformations(QQuickItem* parent /* = nullptr */):
  QQuickItem(parent)
{
}

void ListTransformations::init()
{
  // Register the map view for QML
  qmlRegisterType<MapQuickView>("Esri.Samples", 1, 0, "MapView");
  qmlRegisterType<ListTransformations>("Esri.Samples", 1, 0, "ListTransformationsSample");
}

void ListTransformations::componentComplete()
{
  QQuickItem::componentComplete();

  // get data path
  const QUrl dataPath = QUrl(defaultDataPath() + "/ArcGIS/Runtime/Data/PEDataRuntime");

  // connect to TransformationCatalog error signal
  connect(TransformationCatalog::instance(), &TransformationCatalog::errorOccurred, this, [this](Error e)
  {
    if (e.isEmpty())
      return;

    emit showStatusBar(QString("Error setting projection engine directory: %1. %2").arg(e.message(), e.additionalMessage()));
  });

  // Create a geometry located in the Greenwich observatory courtyard in London, UK, the location of the
  // Greenwich prime meridian. This will be projected using the selected transformation.
  const double x = 538985.355;
  const double y = 177329.516;
  m_originalPoint = Point(x, y, SpatialReference(27700));

  // find QML MapView component
  m_mapView = findChild<MapQuickView*>("mapView");

  // Create a map using the light gray canvas basemap
  m_map = new Map(BasemapStyle::ArcGISLightGray, this);

  // Set initial viewpoint of the map
  m_map->setInitialViewpoint(Viewpoint(m_originalPoint, 5000));

  // connect to map loaded signal
  connect(m_map, &Map::doneLoading, this, [this, dataPath]
  {
    // Set the TransformationCatalog path
    TransformationCatalog::setProjectionEngineDirectory(dataPath.toString());
    if (TransformationCatalog::projectionEngineDirectory().length() > 0)
      emit showStatusBar(QString("Projection engine directory set: %1").arg(TransformationCatalog::instance()->projectionEngineDirectory()));

    // get the initial list of transformations
    refreshTransformationList(true);
  });

  // add graphics to the map view
  addGraphics();

  // set map to map view
  m_mapView->setMap(m_map);
}

// Create a GraphicsOverlay with two Graphics - one to hold the default
// transformed geometry, and the other to use the selected transformation
void ListTransformations::addGraphics()
{
  // Create the original graphic
  SimpleMarkerSymbol* blueSquare = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle::Square, QColor("blue"), 20.f, this);
  m_originalGraphic = new Graphic(m_originalPoint, blueSquare, this);

  // Create the projected graphic
  SimpleMarkerSymbol* redCross = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle::Cross, QColor("red"), 20.f, this);
  m_projectedGraphic = new Graphic(m_originalPoint, redCross, this);

  // Create the Overlay
  GraphicsOverlay* overlay = new GraphicsOverlay(this);
  m_mapView->graphicsOverlays()->append(overlay);
  overlay->graphics()->append(m_originalGraphic);
  overlay->graphics()->append(m_projectedGraphic);
}


void ListTransformations::refreshTransformationList(bool orderBySuitability)
{
  // get the input/output spatial reference
  SpatialReference inSpatialReference = m_originalGraphic->geometry().spatialReference();
  SpatialReference outSpatialReference = m_map->spatialReference();

  // request the transformations
  if (orderBySuitability)
    m_transformations = TransformationCatalog::transformationsBySuitability(inSpatialReference, outSpatialReference, m_mapView->visibleArea().extent());
  else
    m_transformations = TransformationCatalog::transformationsBySuitability(inSpatialReference, outSpatialReference);

  // update the QML property list
  m_transformationList.clear();
  for (DatumTransformation* transformation : qAsConst(m_transformations))
  {
    QVariantMap transformationMap;
    transformationMap["name"] = transformation->name();
    transformationMap["isMissingProjectionEngineFiles"] = transformation->isMissingProjectionEngineFiles();
    m_transformationList.append(transformationMap);
  }

  // update the property
  emit transformationListChanged();
}

void ListTransformations::updateGraphicTransformation(int index)
{
  GeographicTransformation* transform = static_cast<GeographicTransformation*>(m_transformations.at(index));
  if (transform->isMissingProjectionEngineFiles())
  {
    QString missingFiles = "Missing grid files: ";
    const QList<GeographicTransformationStep> steps = transform->steps();
    for (const GeographicTransformationStep& step : steps)
    {
      const auto filenames = step.projectionEngineFilenames();
      for (const QString& filename : filenames)
      {
        missingFiles += filename;
      }
    }
    emit showStatusBar(missingFiles);
  }
  else
  {
    Geometry projectedPoint = GeometryEngine::project(m_originalPoint, m_map->spatialReference(), transform);
    m_projectedGraphic->setGeometry(projectedPoint);
  }
}

Your browser is no longer supported. Please upgrade your browser for the best experience. See our browser deprecation post for more details.