# Using in-memory spatial index **URL:** \ **Category:** Services\ **Created:** [February 20, 2013, 12:11pm UTC](https://community.thinkgeo.com/t/using-in-memory-spatial-index/7179 "2013-02-20T12:11:37Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Raul](https://community.thinkgeo.com/letter_avatar_proxy/v4/letter/r/958977/32.png) [@Raul](https://community.thinkgeo.com/u/Raul)\ **Post date:** [February 20, 2013, 12:11pm UTC](https://community.thinkgeo.com/t/using-in-memory-spatial-index/7179/1 "2013-02-20T12:11:37Z")
Hello, I am trying to use an in-memory spatial index and got into trouble. File-based RtreeSpatialIndex works without errors but it is too slow for our needs, so I thought of handling StreamLoading event and assigning a MemoryStream to args.AlternateStream. This approach fails when I try to open the index:     System.IndexOutOfRangeException occurred   HResult=-2146233080   Message=Index was outside the bounds of the array.   Source=MapSuiteCore   StackTrace:        at hxQ=.RU4=.khQ=(BinaryReader SU4=) Extended stack trace:   MapSuiteCore.dll!hxQ=.RU4=.khQ=(System.IO.BinaryReader SU4=) + 0x10c bytes   MapSuiteCore.dll!hxQ=.h0A=.khQ=() + 0x90 bytes   MapSuiteCore.dll!hxQ=.PjY=.VzY=() + 0x14 bytes   MapSuiteCore.dll!hxQ=.PjY=.Dxg=(string UzY=, bool VDY=, ThinkGeo.MapSuite.Core.RtreeSpatialIndex.q0Y= VTY=) + 0x97 bytes   MapSuiteCore.dll!ThinkGeo.MapSuite.Core.RtreeSpatialIndex.OpenCore() + 0x7f bytes   MapSuiteCore.dll!ThinkGeo.MapSuite.Core.SpatialIndex.Open() + 0x22 bytes   I also tried to use RtreeSpatialIndex.CreatePointSpatialIndex(filePath,...) and initialize the memory stream with the content of the .idx file. That got me past Open() but failed on Add():   System.NullReferenceException occurred   HResult=-2147467261   Message=Object reference not set to an instance of an object.   Source=MapSuiteCore   StackTrace:        at hxQ=.YE4=.bE4=(String bU4=)        at ThinkGeo.MapSuite.Core.RtreeSpatialIndex.bUY=(Double bkY=, Double b0Y=, String cEY=)        at ThinkGeo.MapSuite.Core.RtreeSpatialIndex.bUY=(PointShape cUY=, String ckY=)        at ThinkGeo.MapSuite.Core.RtreeSpatialIndex.AddCore(Feature feature)        at ThinkGeo.MapSuite.Core.SpatialIndex.Add(BaseShape baseShape)   I also looked for samples or at least posts on handling Rtree's StreamLoading event but didn't find any. Any suggestions would be appreciated.    Thanks in advance, Raul     ---
**Author:** ![Johnny](https://community.thinkgeo.com/user_avatar/community.thinkgeo.com/johnny/32/19044_2.png) [@Johnny](https://community.thinkgeo.com/u/Johnny)\ **Post date:** [February 21, 2013, 2:37am UTC](https://community.thinkgeo.com/t/using-in-memory-spatial-index/7179/2 "2013-02-21T02:37:54Z")
  Hi Raul, Welcome to Map Suite discussion forum and thanks for your posts. I guess maybe there are 2 problems here shown as following: 1.       In MapSuiteCore.dll, all the MemoryStream used here should follow the .idx data format. Otherwise, it will throw the exception. 2.       I guess your workaround is really a workable way, but missed setting the “rTreeIndex.ReadWriteMode =RtreeSpatialIndexReadWriteMode.ReadWrite;”. Please check the demo code shown below:   `        public TestForm()        {            InitializeComponent();        }        string idxFilePath;        private void TestForm_Load(object sender, EventArgs e)        {            idxFilePath =  @"..\..\~.idx";            RtreeSpatialIndex rTreeIndex = new RtreeSpatialIndex(idxFilePath, RtreeSpatialIndexReadWriteMode.ReadOnly);            rTreeIndex.StreamLoading += new EventHandler(rTreeIndex_StreamLoading);            RtreeSpatialIndex.CreateRectangleSpatialIndex(idxFilePath, RtreeSpatialIndexPageSize.EightKilobytes);            rTreeIndex.ReadWriteMode = RtreeSpatialIndexReadWriteMode.ReadWrite;            rTreeIndex.Open();            rTreeIndex.Add(new PointShape(0, 0));        }        void rTreeIndex_StreamLoading(object sender, StreamLoadingEventArgs e)        {            FileStream fs = new FileStream(idxFilePath, FileMode.Open, FileAccess.ReadWrite);            byte[] bytes = new byte[fs.Length];            fs.Read(bytes, 0, (int)fs.Length);            MemoryStream memoryStream = new MemoryStream(bytes);            e.AlternateStream = memoryStream;        }`   Thanks, Johnny ---
**Author:** ![Raul](https://community.thinkgeo.com/letter_avatar_proxy/v4/letter/r/958977/32.png) [@Raul](https://community.thinkgeo.com/u/Raul)\ **Post date:** [February 22, 2013, 1:40pm UTC](https://community.thinkgeo.com/t/using-in-memory-spatial-index/7179/3 "2013-02-22T13:40:20Z")
Hey Johnny, Thanks a lot for your reply, the sample code you provided worked with a small correction: creating MemoryStream(byte[]) creates a non-resizable stream based on that byte array. Instead, we'd like something like  `    var memoryStream = new MemoryStream();    memoryStream.Write(bytes, 0, bytes.Length);` Regards, Raul ---
**Author:** ![Johnny](https://community.thinkgeo.com/user_avatar/community.thinkgeo.com/johnny/32/19044_2.png) [@Johnny](https://community.thinkgeo.com/u/Johnny)\ **Post date:** [February 25, 2013, 3:18am UTC](https://community.thinkgeo.com/t/using-in-memory-spatial-index/7179/4 "2013-02-25T03:18:11Z")
That’s great, any question please feel free to let us know.      Thanks,   Johnny