topic Re: Using Generate Near Table in Spatial Data Science Questions

Using Generate Near Table

BrianKneller — Thu, 03 Dec 2015 21:32:18 GMT

Hi I have an issue with the above tool. I am spatially relating many points to a line, the points (input features held in gdb) are arranged in a line parallel to and near to another line (near feature held in folder), I use the output table generated by the system. Both input features have the same geo co-ords and projections. If I select planar I get a set of results which fall within the range bounding the parallel lines. If I select Geodesic I get a set of results outside the parallel line extent. My projection is Mars2000_EquidistantCylindrical_CLON0 and the geographic co ord system, spherical. My problem extent ranges over a 10km square approx. and I am surprised that the geodesic results are so different, I suspect I should have done a reprojection ?,

I would appreciate any suggestions / advice please

Re: Using Generate Near Table

DanPatterson_Retired — Thu, 03 Dec 2015 21:42:55 GMT

Have you tried using a dataset in projected coordinates? On a totally unrelated issue with creating Voronoi Diagrams, the problem went away when the data were physically projected (not just in a dataframe with a projection set). You area is small enough that the results shouldn't be compromised in any large way.

Re: Using Generate Near Table

BrianKneller — Fri, 04 Dec 2015 17:39:32 GMT

Hi Dan, Thanks for your response, I suspected I should do this, I am using Near (planar) to get the locations of the lines between the input feature and near feature then using XY_Line to create a shape file, this is geodesic and this tool enforces the spatial references - pity Near does not.

I have two other issues with "Near" which are more generic and probably due to my lack of understanding.

I have a feature class for "Lower Lines" e.g. and I have a set of line variants within this Class each one with its own layer. I have tried to select a Near Feature by selecting the appropriate layer and it always selected the polyline with the lowest OID. So I used "define query" in the layer to spec the Lower Line variant and still does not seem to work - it seems I should have a separate feature class / layer if I want variants with "Near" of maybe I should check the select again?

My User name has a space in it and "Near" does not allow a table name with a space if it is assigned to a folder, "Near" will allow a table name with a space if it goes to the gdb, is there a work around for this as I don't want to change my Windows username and I need to store some data externally due to space constraints.

Thanks again

Re: Using Generate Near Table

DanPatterson_Retired — Fri, 04 Dec 2015 18:18:12 GMT

When doing geometric calculations, I only work with local copies in projected coordinate systems. I have never had the need to work over large distances for a Near calculation. The algorithm being used for the geodetic calculation is not published and I haven't had time to test-amate what it might be so I avoid them. Is there the remotest chance that a Near calculation would require extremely fine precision or accuracy ? (ie will nearest features come down to differences in the order of millimeter, centimeters, meters, kilometers etc)

Sorry I can't help more since I don't use anything network related (physical or cloud)...other than to store zips of the days events.