Latest Contributions by RichardFairhurst

I ran a test run, and although the fields are populated, their units aren't in miles.  I must be missing something simple...  I am using Arc10, and I have converted to an appropriate equal distance projection.  Regards... I am not sure how much influence the dataframe has on the field calculator.  I suspect it only uses the native projection and units of the feature class when you just put !Shape.Length!. If you are OK with the original projection of the feature class, at 10 I believe if you choose the Python 9.3 option in the Model Builder Field Calculator tool you can adjust units by using: !Shape.Length@Miles! # or substitute any other appropriate units for Length. I am not sure how to emulate the geometry calculator's ability to apply the dataframe projection to feature classes that were stored using a different projection through the field calculator (At least not in Python.  At 9.3 VBA would do it, but not at 10 using VB script). ... View more

Richard, the field calculation for !SHAPE.LENGTH! / 5280 # does not work.  It produces a syntax error when ran on an empty field through field calculation.  Any thoughts? What version of ArcGIS are you using and are you doing this in Desktop or with Model Builder.  This should work for ArcGIS 9.3 and up, although you may have to change the case of the words to mixed case for 10 when ESRI started to make Python case sensitive.  At 10 you can do: !Shape.Length@miles! # to get miles At 9.2 I think you can only use Python in Model Builder and the syntax might be !Shape!.Length or some other variant.  Check the help files, since there should be something on this for 9.2.  If you will not be exporting to a Python script and running it directly in Model Builder you can use VBA in an advanced calculation at 9.2, where the syntax would be: Parser: VBA Pre-Logic Code: Dim dblLength as double Dim pCurve as ICurve Set pCurve = [SHAPE] dblLength = pCurve.Length / 5280 Expression: dblLength ... View more

Thanks for you quick reply, although am not certain I'm following your logic precisely.  And yes, I am using feature classes.  When calculating without model builder, I create the two fields to house mileage (total miles and need miles), use calculate geometry to populate the segmets mileage, and then perform frequency analysis to summarize the values of the HUC 12s.  Using model builder,  should I be using calculate field prior to utilizing frequency, and what calculation would work for empty fields? Thanks again! I overcomplicated the calculation.  It can be done as a simple calculation: Parser:  Python Expression: !SHAPE.LENGTH! / 5280 # assumes base units is in feet and you want miles. The above calculation is done using the Field Calculator tool and does what the Calculate Geometry tool does in ArcMap, so you would use it the same way that you use the Calculate Geometry tool in your desktop process.  This Field Calculator expression is what you had to do in ArcMap versions that existed when you had no Calculate Geometry option.  With the Total_Miles and Need_Miles values calculated you would run the Frequency tool the same way you do now. You should run a calculation on Need_Miles to populate it with 0 on all records that are Null and that you do not want to be in the subset that has Mileage calcuated into the Need_Miles field prior to running Frequency, unless you find that the Frequency tool does what you want when these values are Null. ... View more

I've tried all of the suggestions without any luck.  The only way that I can get it to extract the data is if I use: !shape.firstpoint! What's worse is that I have to have the field type set to text!  So, I end up with:  -92.298060755811 41.6208860260915 in my destination field.  I have been able to populate my desired fields from these fields and convert it to a double, but it has been a real pain. I'm running ArcInfo 9.2 does that make a difference on the syntax? Thanks At 9.2 you could not use a method to access the X or Y component of the coordinate directly.  That capability first appeared at 9.3.  You had to parse the coordinates to get each desired coordinate separated and cast them to a float for directly calculating them to a pair of double fields.  That avoids first saving the whole string to a text field.  I don't have access to 9.2 anymore, but as I recall the syntax works something like: float(!shape.firstpoint![0]) # for X coordinate.  float(!shape.firstpoint![1]) for Y coordinate. ... View more

Hello: I am attempting to calculate linear mileage of stream data for three predefined fields in model builder.  The conceptual approach is to calculate all segments mileage in the first field (total_miles), then calculate a fraction of the records in another field (need_miles), and finally, calculate the percentage of the two in the final field (percentage).  I'll use frequency to agregate the segments to their respective HUC 12 areas.  The problem I am having, is how to calculate geometry (linear mileage) in model builder?  I can't seem to locate the tool that may be dragged to model builder.  Thanks so much in advance!!!! A few ways to do this.  Sum the Length value in the frequency in whatever units they are listed (assming this is a geodatabase and not a shapefile), then do the conversion to miles at the join and calculation stage.  If you are using a shapefile, first calculate a field called MILES using the Field Calculator tool.  The python calculation to get the length of a line and make the appropriate units conversion is: Parser:  Python Pre-Logic Code: def Output(Length):   return Length / 5280 # assumes that shape length is in Feet and is being converted to Miles. Expression: Output(!SHAPE.LENGTH!) now sum the MILES field values in your frequency and you can get the all of the fields filled in that you need. ... View more

I am using shapefiles, does that matter? I think the problem is in the fact that the fc variable is a numeric value and not a feature class because it has been converted to an enumerated value.  The CreateFeatureLayer expects fc to be an actual feature class and not a number.  Separte the enumeration variable i from the fc variable.  Try the code below: arcpy.env.workspace = 'C:\\GIS_DATA\\' # or r 'C:\GIS_DATA\' mxd = arcpy.mapping.MapDocument("Current") fclist = arcpy.ListFeatureClasses() i = 0 for fc in fclist:     i += 1     arcpy.CreateFeatureLayer_management(fc, "layer_%i" % i) ... View more

If your field contains string/text data, there is no need for the len method in Python since string data is an "iterable".  For example >>> a = "abcdefghijklmnop" >>> b = a[:-4] >>> b 'abcdefghijkl' >>> Dan: I am not really a Python programmer and my expression above would not work anyway because I didn't notice (in my quick check of some Python websites) that I needed the colon to indicate to take everything from the beginning of the string to the second position.  Thanks for correcting my Python ignorance and showing another example of where Python is more elegant than VB Script. ... View more

Thank you very much. Yes I thought about this possibility. The Linear Referencing model we use is not suitable for Network Analyst (Route not connected) and it's managed externaly, we can't modify it. However I can create a network that interconnect my LRS model and define rules and direction of travel (for a motorway it shouldn't be to hard). Then I can create a geoprocessing tool that draws the "shortest route" based on the user defined "start" and "end" points and relocate the linear result on my LRS Route Model. It's sounds a bit like a makeshift job and I wanted to know if anyone knows another way of doing it. If by your Routes are not connected you mean that you do not have intersection breaks, that is not necessary for Network Analyst.  It can detect and use joins where lines cross if you configure it that way.  Also if you can create a network that interconnects your LRS model that should work equally well as an input to Network Analyst.  Also the resulting route you want will not be able to keep the original measures of your Routes without being screwed up anyway, and you would have to use a Route transfer tool to take events from one Route and apply them to the other to match between these new Routes and your original Routes. The bigger problem is that you do not control the network, so some method of incremental updates of a derivative in-house network would be necessary to integrate it with Network Analyst.  That is acheivable by making a copy of the original network and adding a field that keeps track of the end coordinates and length of each line, which can be calculated on your copy and joined to your own in-house-network.  Using that field you can easily detect lines that have changed each time you get a new update of the Routes. Again, your idea that this is somehow a simple geoprocessing tool to create is incorrect.  The amount of time you will spend to orient the routes, identify join points and then deal with the user failing to follow your orientations when they set beginning and ending points alone will give you headaches.  I doubt Python can really do the interface you want.  Every step you have described that you would do with your network is how you set up Network Analyst and Network Analyst has already overcome all of the logic it takes to traverse a network from any point to any point, even on networks without line breaks at each intersection, so again why reinvent the wheel? ... View more

Just in case you ever need to use the field calculation in a Python script, to do the same thing in Python you would also use the len() function.  For example: !input![len(!input!)-4] or rstrip(!input![len(!input!)-3]) (Keep in mind that whitespace characters count, so in your examples "BN14 5RY" is 8 characters long, not 7 and "BN1 5RY" is 7 characters long, not 6.) ... View more

Hello, I have postcodes which I need to cut down from say BN14 5RY to only BN14. I cannot simply use the 'left(input, n)' equation as some postcodes are only 6 figures long such as BN1 5RY and I always need the first 3/4 characters. Does anyone know a way to delete the last 3 characters? Thanks in advance. You can use the left() function if you combine it with the len() function.  This will do what you want (I assumed you also want to get rid of the space character and not just the last three non-whitespace characters): left(input, len(input) - 4) or rtrim(left(input, len(input) - 3)) The len() function is normally used in combination with the left(), mid() and right() functions to control starting points, ending points and number of character values when doing string parsing. ... View more

The whole dialog should be resizable.  I have layers with over 300 symbol categories (sign faces) and you can only see about 6 symbols at a time.  I should be able to resize the horizontal size when I have many codes grouped together and the vertical size of the dialog to be able to see as many values as my screen will fit when I need it. ... View more

I agree. I have a layer with over 300 Unique symbol codes (sign faces). Variant codes for the same sign face do not sort together and to move them together can involve hundreds of clicks on the arrow buttons.  You cannot see enough values in the list to be able to effectively group them and if I later want to ungroup them I get a bug that often makes one or more of the ungrouped symbols unmoveable at the top of the list just below the All Other Values symbol and above the Heading row.  Code conversions and standardizations create the problem all over again. I ought to sue when I develop carpal tunnel syndrom from the current one click at a time arrow interface. The ability to hold down the arrow button to act as a continuous move if held for a few seconds would also be nice. I'd like both drag and drop and continuous arrow movements to work on multiple selected symbols at once also. ... View more

I agree.  I have a layer with over 300 Unique symbol codes (sign faces).  Variant codes for the same sign face do not sort together and to move them together can involve hundreds of clicks on the arrow buttons.  Code conversions and standardizations create the problem all over again.  I ought to sue when I develop carpal tunnel syndrom from this interface. The ability to hold down the arrow button to act as a continuous move if held for a few seconds would also be nice.  I'd like both drag and drop and continuous arrow movements to work on multiple selected symbols at once also. ... View more

when i am working with Attribute Table,i have a problem of changing the name or properties of the already created field name that has records in it.what i always do is just adding another field and calculating all the records in the previous field and delete that field.These affects the sequence of fields added.HOW CAN I SOLVE THIS TYPE OF PROBLEM? Any ideas or recommendations? Seid If you have Microsoft Access and the original ObjectID order of your original feature class is not important to preserve (for relationship classes or other multi-table key fields) the easiest way to do this is to create a personal geodatabase.  You can export the whole feature class into the personal geodatabase, but there may be a loss of spatial precision if your source data is in SDE or a file geodatabase.  However, all you really need is the feature class field structure, which can be exported from the original feature class without records by adding a definition query to the data that filters out all records and doing an export. In Access you can open the personal geodatabase file and rename, rearrange, and redefine the field structure of your feature class anyway you want easily (but that is the only easy part).  If you do not need to preserve spatial precision for SDE or a file geodatabase and you exported all of the original features, this restructured feature class can replace your original feature class and you do not need to do anything else. If you need to preserve the original data's spatial precision then after all the fields are laid out in Access the way you want, create a new feature class in the original workspace and import all of the spatial characteristics of your original layer.  Import the field structure from the restructured personal geodatabase file. Now reload the data from the original feature class.  Renamed fields will need to be matched in the load process.  If you want to downgrade a double to a long or short, you need to have a temporary double field in the structure to transfer the data from the original, since you cannot match a double to anything but a double or a string field in the load dialog (longs cannot become shorts directly either, only long, double or string).  String values that you want to convert to dates or numeric values should also be loaded into temporary string fields rather than directly into the new date or numeric fields to avoid load errors and record losses from bad conversions.  After the load completes calculate over any double values to your long/short permanent fields and any strings that are to become dates or numeric values into their new fields and delete the temporary double/string fields. Obviously this is a pain to do even using the above method, since there are so many steps, but ESRI has no functionalty that comes close to what Access is capable of doing.  (This may not work for certain complex feature classes that cannot use the simple load dialog, such a network built using Network Analyst). If preservation of the original ObjectID values is essential and they cannot be altered in any way, there is no simple way to do this.  If you are willing to rebuild the relationship keys to match a new set of ObjectID values, then the above methods can be used if you first create a temporary field to hold the original ObjectID values of your original data prior to any restructuring.  Then you can use that temporary ObjectID value as a join to recalculate all of the foriegn keys in your related tables/feature classes to the new ObjectID of your new feaure class.  After that you can rebuild your relationship classes. ... View more

Hello, I work for a Motorway Maintenance Organisation. We use the Linear Referencing System as base of our location system. Our network is divided in many "Routes" (LRS Model). I want to implement a geoprocessing tool that allow the users to generate "Lines" features automatically, based on start and end points they define. Concept: The user enter a "start" and "end" point (Click on the Map) The geoprocessing tool locates these points (Locate feature along route) and then generate a new line feature (Make Route Event Layer). This is my problem: I don't know how it is possible to manage the "connexions" between the "Routes" with the Linear Referencing System. If the start and end points are on differents routes that are connected in the real world, how is it possible for the Linear Referencing System to detect this connection and for the "make route event layer" to "jump" from one Route to another ? Has someone have already work on that ? What you are wanting is a Network Analyst function rather than a something you would do with a pure Linear Referencing interface.  Linear Referencing is designed for facility management of a single route, bot not on an interconnected network of routes that can be traversed in numerous ways.  However, Network Analyst can easily generate a multi-street route (with M values I believe) between any end points you may set on different roads according to whatever network connectivity and turn restriction configurations you want to set up.  Of course you have to have licenses for that extension and have to build a Network Analyst network to use it.  Effectively you would have to reconstruct all of the Network Analyst functionality to develop an interface that does what you want if you tried to do it with just a Linear referenced network, so instead you should just purchase licenses for Network Analyst and not reinvent the wheel.  Perhaps a geometric network could also do some of what you want, but it follows rules that are more oriented to Utility Networks, while Network Analyst is more oriented to transportation networks. I have limited experience with Network Analyst, but I beleive the output initially would create a single route ID on multiple line segments with one segment for each road traversed.  However, that output could be combined into a new single line Route using the Create Route tool on the Network Analyst output's Route ID.  That new Route could be then used for placing Linear Referencing events that could fall anywhere along those connected streets between the two end points. If you restrict your users to working within a single predefined Linear Referenced route, I might be able to assist you with interfaces and code for creating line events that fall along it, but not to generate new routes that logically traverse a network across multiple streets. ... View more