[GIS] How to convert existing fields to lat and long using the Calculate Field tool

arcgis-9.3arcobjects

I am trying to convert my X and Y fields from feet to lat and long. I can easily do this in Calculate Geometry from the attribute table, but I'm needing to use this in a model and Calculate Geometry is not available as a tool. I'm using the Calculate Field tool and trying to find a script that converts this to lat and long. I've tried the following script using the advanced code for VBA with no luck:

Dim dblX As Double
Dim pPoint As IPoint
Set pPoint = [Shape]
dblX = pPoint.X

dblX

I'd like to avoid having to create a totally new shapefile or feature class. I just want to change the existing fields in this existing feature class.

Thanks!!

Best Answer

Here are some Calculate Field examples. If you scroll down about 3/4 of the way you'll see some examples for Geometry Unit conversion.

For scripting, you might consider adding fields as opposed to editing existing ones.

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[GIS] How to preserve original direction of NHD segments when creating route using gp.CreateRoutes_lr tool

So after trying every possible scenario I could imagine, I finally stumbled on why the Create Routes tool was arbitrarily flipping the direction of the NHD stream segments. In the tools's online information, you can choose to either use the geometric length to obtain the routes, or custom fields you have created as one field or two field for the input of specifying how routes will be obtained. The default is the "Length" option and I had actually used that default for another script that was calculating a per-NHD-segment feature class, and it worked fine in that script. But, because I was using multiple NHD segments to create the route, such a scenario is when apparently you need to use the two field option.

So I added a "FromM" field for the "from measurement", and a "ToM" field for the "to measurement" to the dissolved NHD segments before creating my route. I calculated the "FromM" value to zero, and the "ToM" value to "!Shape_Length!". I then modified the CreateRoutes input accordingly, and the script worked fine.

This is exactly why "default" selections for software tools like this is really dangerous. I know I should be more diligent in researching all options for each input of a tool and for the most part I am. But even in this case had I done that, and I had poured over the online help and searched online high and low, not sure I would have been enlightened. This is not the first time ESRI default values have tripped me up. But, it's a double problem when the information on the tool really doesn't elucidate the implications of the options for a particular input when a default is specified (at least as far as I can tell with tis particular instance). Either way, note that during my testing and debugging that the tool was not consistently flipping the direction for every dissolved set of segments, only certain ones (and not sure what drives that) which made it even more tricky to figure out what the issue was. Anyhow...onward and upward

[GIS] Get coordinates from current view using arcobjects

I would recommend using the IActiveView.Extent property. You can cast an IMap to an IActiveView and vice versa. http://resources.arcgis.com/en/help/arcobjects-net/componenthelp/index.html#//001200000199000000

The Extent property will return an IEnvelope that has an X and Y Max and Min that you can use to calculate the center if you would like.
http://resources.arcgis.com/en/help/arcobjects-net/componenthelp/index.html#//002m00000169000000

To get the IActiveView instance you can use the IApplication.Document property and cast the Document to an IMxDocument. You can then get an IActiveView using IMxDocument.ActiveView property. http://help.arcgis.com/en/sdk/10.0/arcobjects_net/componenthelp/index.html#//004900000054000000

Some code-

Dim mxDocument As ESRI.ArcGIS.ArcMapUI.IMxDocument = CType(application.Document, ESRI.ArcGIS.ArcMapUI.IMxDocument) ' Explicit Cast
Dim activeView As ESRI.ArcGIS.Carto.IActiveView = mxDocument.ActiveView
Dim currentExtent As IEnvelope = activeView.Extent
//TODO::  Get Max/Min X and Y from currentExtent and calculate the center point.

Here is a gis.stackexchange post that describes taking a map x,y and converting it to a lat, long. Extracting lat/long from screen when using British National Grid projection in ArcGIS Desktop?

In particular, follow these steps-

I'm not that familiar the the British National Grid, but it appears that a datum transformation is required when projecting to WGS84.

So, use ISpatialReferenceFactory.CreateGeoTransformation to create the appropriate datum transformation, and ISpatialReferenceFactory.CreateGeographicCoordinateSystem to create the target (WGS84) spatial reference.

Finally, cast the point into IGeometry5 and call ProjectEx, passing the target spatial reference and the geotransformation. IPoint.X and IPoint.Y should then represent longitude and latitude of the point where the user clicked.

Best Answer

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