GPS incorrect in sample

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urban forestry planner
Posts: 17
Joined: Tue May 01, 2007 10:31 am

GPS incorrect in sample

Post by urban forestry planner » Fri Oct 12, 2007 2:07 pm

I ran a sample and the GPS coordinates for every segment were exactly the same. BTW, we are a city of 90,000. Anyone know why?

Thanks
StormyJerry

Not sure

Post by StormyJerry » Mon Oct 15, 2007 9:43 am

Thanks for this perplexing question. Here is the response of our GIS specialist when I passed your question to him:
When you say segments, it sounds as if you are refering to the sample street segment generator? If so:
Unlike points, line segments or arcs do not have single GIS coordinates, but of course are made up of two or more sets of coordinates. So if you are looking at say a table of attributes attached to the line (road) layer, you may be seeing something entirely unrelated to the sample generator. As long as you are getting a subset of street segments that are randomly distributed throughout the city, then you are getting the data you need.

If you are refering to the UFORE plot generator, then one of the following is probably occuring:
1) You have the same coordinates, but the points are indeed scattered spatially and randomly across the city - the XY coordinate attributes are not being updated. Use the ArcGIS help via the Field Calculator tool in the table view to see an easy way to get these values updated.
2) You have the same coordinates, and plot points are stacked on top of each other at one location - as you might imagine this is more problematic and probably relates to either the version of ArcGIS you are running and/or to the other base data you have loaded in (i.e. the projection system and units). For this, please provide addition info on version and projection system, as well as what other layers you have loaded up when you run the plots.
Hope that helps. Please fill in the missing details if you are still having problems so we can better understand your situation.
urban forestry planner
Posts: 17
Joined: Tue May 01, 2007 10:31 am

Post by urban forestry planner » Tue Oct 16, 2007 3:48 pm

I am referring to the sample segment generator for SDAP. It gives a written segment report. For each segment, it gives the street name, street addresses to be included in the sample, length of segment and the "from" and "to" coordinates of each segment . It's the "from" and "to" coordinates that are exactly the same for all sample segments.
Thanks.
StormyJerry

Getting closer...

Post by StormyJerry » Wed Oct 17, 2007 9:27 am

Those are begining and ending addresses, left and right side of the street. If they are all the same, I suspect something was wrong with the TIGER/Line files you used or with the version of the Street Segment Generator.

Can you confirm that you downloaded the correct shapefile: "Line Features - Roads" for your county, and that you used the correct polygon for your community selected out of the shapefile "Designated Places 2000" for your county?

Also, can you please indicate which version of ArcGIS you are using and confirm that you selected the correct corresponding *.dll (as described in the Manual, Section 3.4.1, step 4)?

Thanks.
urban forestry planner
Posts: 17
Joined: Tue May 01, 2007 10:31 am

Post by urban forestry planner » Fri Oct 19, 2007 12:10 pm

Everything you mentioned is OK from this end as far as I can tell. I'm not talking about the addresses. Those are correct. I'm talking about the "From" and "To" GPS coordinates being all the same. They are above the street addresses and below the "length of the feature" line. They all read:

The From coordinates are: -80.002161 37.310635
The To coordinates are: -80.004956 37.310987

Thanks
StormyJerry

Now I get it!

Post by StormyJerry » Fri Oct 19, 2007 1:37 pm

So that somebody else can follow along, here are the title and first section of one of my full segments reports that will illustrate what we have been trying to discuss, with the two troublesome lines in bold:
REPORT GIVING ADDRESS RANGE OF THE SELECTED FEATURES

The Map units are: Decimal_Degrees
The Distance units are: miles

The name of the feature is: Maywood St
The length of the feature is: 0.20332 miles
The From coordinates are: -80.41541244 37.26517959
The To coordinates are: -80.41271244 37.26687959

The Right address range of the feature is: 100-212
The Left address range of the feature is: 101-215
I don't believe I have ever looked at this full report! There are no GPS coordinates associated with the TIGER/Line file that the Street Segment Generator is using, so I will hazard a guess that the coordinates are just the center point of the community whose polygon you are using to clip the road shapefile in ArcGIS. I will check with our GIS specialist on this and add a post if there is a better explanation.

Either way, there does not seem to be a need for those lines at all in the Report, and we will look at removing them from the next release. Thanks.

PS: Sorry it took us so long to understand what exactly you were talking about.
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