Table of Contents

Class InMemoryGridFeatureSource

Namespace
ThinkGeo.Core
Assembly
ThinkGeo.Core.dll

Reads cell data from a grid file and displays them in appropriate colors based on their values.

public class InMemoryGridFeatureSource : FeatureSource
Inheritance
InMemoryGridFeatureSource
Inherited Members

Remarks

The GridFeatureSource displays cells with different colors in a rectangle area of map. The color of a cell depends on the cell value in the grid file. The grid file provides information about the grid, such as rows and columns number, cordinate of lower left corner, cell size, and values of cells.

Constructors

InMemoryGridFeatureSource()

This is the constructor the for the class. If you use this constructor then you need to set the required properties manually.

public InMemoryGridFeatureSource()

Remarks

None

InMemoryGridFeatureSource(GridCell[,]) 

public InMemoryGridFeatureSource(GridCell[,] gridMatrix)

Parameters

gridMatrix GridCell[,]

Properties

CellSize

Gets the cell size of the grid.

public double CellSize { get; }

Property Value

double

ColumnCount

Gets column number of the grid.

public int ColumnCount { get; }

Property Value

int

DataValueColumnName 

public string DataValueColumnName { get; }

Property Value

string

GridMatrix 

public GridCell[,] GridMatrix { get; set; }

Property Value

GridCell[,]

IsEditable

This property returns if the FeatureSource allows edits or is read only.

public override bool IsEditable { get; }

Property Value

bool

Remarks

This property is useful to check if a specific FeatureSource accepts editing. If you call the BeginTransaction and this property is false then an exception will be raised.

For developers who are creating or extending a FeatureSource it is expected that you override this virtual method if the new FeatureSource you are creating allows edits. By default the decimalDegreesValue if false meaning that if you want to allow edits you must override this method and return true.

LowerLeftPoint

Gets LowerLeft PointShape of the grid.

public PointShape LowerLeftPoint { get; }

Property Value

PointShape

NoDataValue

Gets the NoDataValue in the grid.

public double NoDataValue { get; }

Property Value

double

RowCount

Gets row number of the grid.

public int RowCount { get; }

Property Value

int

Methods

CloseCore()

This method closes the FeatureSource and releases any resources it was using.

protected override void CloseCore()

Remarks

This protected virtual method is called from the concreate public method Close. The close method plays an important role in the life cycle of the FeatureSource. It may be called after drawing to release any memory and other resources that were allocated since the Open method was called.

It is recommended that if you override this method that you take the following things into account. This method may be called multiple times so we suggest you write the so that that a call to a closed FeatureSource is ignored and does not generate an error. We also suggest that in the close you free all resources that have been opened. Remember that the object will not be destroyed but will be re-opened possibly in the near future.

CommitTransactionCore(TransactionBuffer)

This method will commit the existing transaction to its underlying source of data.

protected override TransactionResult CommitTransactionCore(TransactionBuffer transactions)

Parameters

transactions TransactionBuffer

This parameter encapsulates all of the adds, edits and deleted that make up the transaction. You will use this data to write the changes to your underlying data source.

Returns

TransactionResult

The return decimalDegreesValue of this method is a TransactionResult class which gives you the status of the transaction you just committed. It includes how many of the updates, adds, and deletes were successful and any error that were encountered during the committing of the transaction.

Remarks

This method will commit the existing transaction to its underlying source of data. It will pass back the results of how the commit went to include any error received. If you are implementing your own FeatureSource then this is one of the crucial methods you must create. It should be fairly straight forward that you will loop through the transaction buffer and add, edit or delete the InternalFeatures in your underlying data source. Remember to build and pass back the TransactionResult class so that users of your FeatureSource can respond to failures you may encounter committing the InternalFeatures. We will handle the end of the transaction and also the cleanup of the transaction buffer. Your task will be to commit the records and produce a TransactionResult return.

The Transaction System

The transaction system of a FeatureSource sits on top of the inherited implementation of any specific source such as Oracle Spatial or Shape files. In this way it functions the same way for every FeatureSource. You start by calling the BeginTransaction. This allocates a collection of in memory change buffers that are used to store changes until you commit the transaction. So for example when you call the Add, Delete or Update method the changes to the feature are stored in memory only. If for any reason you choose to abandon the transaction you can call RollbackTransaction at any time and the in memory buffer will be deleted and the changes will be lost. When you are ready to commit the transaction you call the CommitTransaction and the collections of changes are then passed to the CommitTransactionCore method and the implementer of the specific FeatureSource is responsible for integrating your changes into the underlying FeatureSource. By default the IsLiveTransaction property is set to false which means that until you commit the changes the FeatureSource API will not reflect any changes that are in the temporary editing buffer.

In the case where the IsLiveTransaction is set to true then things function slightly differently. The live transaction concept means that all of the modification you perform during a transaction are live from the standpoint of the querying methods on the object.

To setup an example imagine that you have a FeatureSource that has 10 records in it. Next you begin a transaction and then call GetAllFeatures, the result would be 10 records. After that you call a delete on one of the records and call the GetAllFeatures again, this time you only get nine records. You receive nine records even though the transaction has not yet been committed. In the same sense you could have added a new record or modified an existing one and those changes are considered live though not committed.

In the case where you modify records such as expanding the size of a polygon those changes as well are reflected. So for example you expand a polygon by doubling its size and then do a spatial query that would not normally return the smaller record but would return the larger records, in this case the larger record is returned. You can set this property to be false as well in which case all of the spatial related methods would ignore anything that is currently in the transaction buffer waiting to be committed. In this case only after committing the transaction would the FeatureSource reflect the changes.

Exceptions

InvalidOperationException

In the event you attempt to call this method on a feature source which is not in transaction it will throw an InvalidOperationException.

GenerateGrid(GridDefinition, GridInterpolationModel, Stream, Func<double, string>)

This method calculates all the cells in the grid and write the value of them into the grid file associates with the stream.

public static void GenerateGrid(GridDefinition gridDefinition, GridInterpolationModel gridInterpolationModel, Stream outputStream, Func<double, string> cellValueToStringFunc = null)

Parameters

gridDefinition GridDefinition

This parameter contains the parameters used to describe the grid.

gridInterpolationModel GridInterpolationModel

This parameter represents the interpolation model for calculating cell value of the grid

outputStream Stream

This parameter represents the stream associates with the output file.

cellValueToStringFunc Func<double, string>

Exceptions

ArgumentNullException

If you pass a null as gridDefinition, there will be a ArgumentNullException thrown.

GenerateGridMatrix(GridDefinition, GridInterpolationModel)

This method calculates all the cells in the grid and returns the result in the form of the GridCell matrix

public static GridCell[,] GenerateGridMatrix(GridDefinition gridDefinition, GridInterpolationModel gridInterpolationModel)

Parameters

gridDefinition GridDefinition

This parameter contains the properties used to describe the grid.

gridInterpolationModel GridInterpolationModel

This parameter represents the interpolation model for calculating cell value of the grid

Returns

GridCell[,]

This method returns the GridCell matrix which is calculated based on the input parameters.

GetAllFeaturesCore(IEnumerable<string>)

This method returns all of the InternalFeatures in the FeatureSource.

protected override Collection<Feature> GetAllFeaturesCore(IEnumerable<string> returningColumnNames)

Parameters

returningColumnNames IEnumerable<string>

This parameter allows you to select the field names of the column data you wish to return with each Feature.

Returns

Collection<Feature>

The return decimalDegreesValue is a collection of all of the InternalFeatures in the FeatureSource.

Remarks

This method returns all of the InternalFeatures in the FeatureSource. You will not need to consider anything about pending transactions as this will be handled in the non Core version of the method.

The main purpose of this method is to be the anchor of all of our default virtual implementations within this class. We wanted as the framework developers to provide you the user with as much default virtual implementation as possible. To do this we needed a way to get access to all of the features. For example, we want to create a default implementation for finding all of the InternalFeatures in a bounding box. Because this is an abstract class we do not know the specifics of the underlying data or how its spatial indexes work. What we do know is that if we get all the records then we can brute force the answer. In this way if you inherited form this class and only implemented this one method we can provide default implementations for virtually every other API.

While this is nice for you the developer if you decide to create your own FeatureSource it comes with a price. The price is that it is very inefficient. In the case we just discussed about finding all of the InternalFeatures in a bounding box we would not want to look at every record to fulfil this method. Instead we would want to override the GetFeaturesInsideBoundingBoxCore and implement specific code that would be fast. For example in Oracle Spatial there is a specific SQL statement to do this operation very quickly. The same holds true with other specific FeatureSource examples.

Most default implementations in the FeatureSource call the GetFeaturesInsideBoundingBoxCore which by default calls the GetAllFeaturesCore. It is our advice that if you create your own FeatureSource that you ALWAYS override the GetFeatureInsideBoundingBox. It will ensure that nearly every other API will operate efficiently. Please see the specific API to determine what method it uses.

Exceptions

InvalidOperationException

In the event you attempt to call this method on a feature source which has not been opened it will throw an InvalidOperationException.

GetBoundingBoxCore()

This method returns the bounding box which encompasses all of the features in the FeatureSource.

protected override RectangleShape GetBoundingBoxCore()

Returns

RectangleShape

This method returns the bounding box which encompasses all of the features in the FeatureSource.

Remarks

This protected virtual method is called from the concreate public method GetBoundingBox. It does not take into account any transaction activity as this is the responsibility of the concreate public method GetBoundingBox. In this way as a developer if you choose to override this method you do not have to consider transaction at all.

The default implementation of GetBoundingBoxCore uses the GetAllRecordsCore method to calculate the bounding box of the FeatureSource. We strongly recommend that you provide your own implementation for this method that will be more efficient

If you do not override this method the means it gets the BoundingBox is by calling the GetAllFeatureCore method and deriving it from each feature. This is a very inefficient way to get the BoundingBox in most data sources. It is highly recommended that you override this method and replace it with a highly optimized version. For example in a ShapeFile the BoundingBox is in the main header of the file. Similarly if you are using Oracle Spatial you can execute a simple query to get the BoundingBox of all of the record without returning them. In these ways you can greatly improve the performance of this method.

Exceptions

InvalidOperationException

If the operation is done under source closed state it will throw a InvalidOperationException.

GetColumnsCore()

This method returns the columns available for the FeatureSource.

protected override Collection<FeatureSourceColumn> GetColumnsCore()

Returns

Collection<FeatureSourceColumn>

This method returns the columns available for the FeatureSource.

Remarks

As this is the virtual core version of the Columns method it is intended to be overridden in inherited version of the class. When overriding you will be responsible for getting a list of all of the columns supported by the FeatureSource. In this way the FeatureSource will know what columns are available and will remove any extra columns when making calls to other core methods. For example if you have a FeatureSource that has three columns of information and the user calls a method and requests four columns of information, something they can do with custom fields, we will first compare what they are asking for to the results of the GetColumnsCore. In this way we can strip out custom columns before calling other Core methods which are only responsible for returning data in the FeatureSource. For more information on custom fields you can see the documentation on the OnCustomFieldsFetch.

Exceptions

InvalidOperationException

In the event you attempt to call this method on a feature source which has not been opened it will throw an InvalidOperationException.

GetCountCore()

This method returns the count of the number of records in this FeatureSource.

protected override long GetCountCore()

Returns

long

This method returns the count of the number of records in this FeatureSource.

Remarks

This protected virtual method is called from the concreate public method GetCount. It does not take into account any transaction activity as this is the responsibility of the concreate public method GetCount. In this way as a developer if you choose to override this method you do not have to consider transaction at all.

The default implementation of GetCountCore uses the GetAllRecordsCore method to calculate how many records there are in the FeatureSource. We strongly recommend that you provide your own implementation for this method that will be more efficient

If you do not override this method the means it gets the count is by calling the GetAllFeatureCore method and counting each feature. This is a very inefficient way to get the count in most data sources. It is highly recommended that you override this method and replace it with a highly optimized version. For example in a ShapeFile the record count is in the main header of the file. Similarly if you are using Oracle Spatial you can execute a simple query to get the count of all of the record without returning them. In these ways you can greatly improve the performance of this method.

Exceptions

InvalidOperationException

If the operation is done under source closed state it will throw a InvalidOperationException.

GetFeaturesInsideBoundingBoxCore(RectangleShape, IEnumerable<string>)

This method returns all of the InternalFeatures of this FeatureSource inside of the specified bounding box.

protected override Collection<Feature> GetFeaturesInsideBoundingBoxCore(RectangleShape boundingBox, IEnumerable<string> returningColumnNames)

Parameters

boundingBox RectangleShape

This parameter represents the bounding box you with to find InternalFeatures inside of.

returningColumnNames IEnumerable<string>

This parameter allows you to select the field names of the column data you wish to return with each Feature.

Returns

Collection<Feature>

The return decimalDegreesValue is a collection of all of the InternalFeatures that are inside of the bounding box.

Remarks

This method returns all of the InternalFeatures of this FeatureSource inside of the specified bounding box. If you are overriding this method you will not need to consider anything about transactions as this is handled by the concreate version of this method.

The default implementation of GetFeaturesInsideBoundingBoxCore uses the GetAllRecordsCore method to determine which InternalFeatures are inside of the bounding box. We strongly recommend that you provide your own implementation for this method that will be more efficient. It is especially important for this method as many other default virtual methods use this for their calculations. We highly recommend when you override this method that you use any spatial indexes you have at your disposal to make this method as fast as possible.

Exceptions

InvalidOperationException

In the event you attempt to call this method on a feature source which has not been opened it will throw an InvalidOperationException.

ArgumentNullException

If you pass a null as the returningColumnNames we will throw an ArgumentNullException.

ArgumentNullException

If you pass a null as the boundingBox we will throw an ArgumentNullException.

OpenCore()

This method opens the FeatureSource so that it is initialized and ready to use.

protected override void OpenCore()

Remarks

This protected virtual method is called from the concreate public method Open. The open method play an important role as it is responsible for initializing the FeatureSource. Most methods on the FeatureSource will throw an exception if the state of the FeatureSource is not opened. When the map draws each layer it will open the FeatureSource as one of its first steps, then after it is finished drawing with that layer it will close it. In this way we are sure to release all resources used by the FeatureSource.

When implementing this virtual method consider opening files for file based source, connecting to databases in the database based sources and so on. You will get a chance to close these in the Close method of the FeatureSource.

Exceptions

InvalidOperationException

In the event you attempt to call this method on a feature source which has already been opened it will throw an InvalidOperationException.