topic Re: determine the radius of a curvature from GPS points ? in Geoprocessing Questions

determine the radius of a curvature from GPS points ?

xavierberlo — Thu, 28 Aug 2014 18:32:58 GMT

Hello,

I have a shapefile of gps positions (sucession of points, with X Y Z data) of hundreds of kilometers of road

and I'd like to know if it possible with ArcGis 10 to determine the radius of each curvature.

Example : I have one segment of a road represented by 100 gps points and I'd like to draw the curves and measure the radius of each curvature.

Is there a tool for that ? Or a script ?

I hope I will be able to find the help I need here because I'm lost.

Thank you

Re: determine the radius of a curvature from GPS points ?

DanPatterson_Retired — Thu, 28 Aug 2014 18:54:32 GMT

We did some work in that area a number of years ago ( see the references in this link ) but I have not updated the old extension to ArcGIS

Re: determine the radius of a curvature from GPS points ?

RiyasDeen — Fri, 29 Aug 2014 07:16:48 GMT

Hi Xavier,

Not sure if there are any readily available tool.

Attached script calculates the radius of curvature using three consecutive coordinate sets. In your case you may want to use the start, mid point and end point coordinates for your road.

Re: determine the radius of a curvature from GPS points ?

DanPatterson_Retired — Fri, 29 Aug 2014 11:39:00 GMT

We ruled out a simple selection of 3 points and had to implement circular regression to best fit the gps data...read the paper for more details.

Re: determine the radius of a curvature from GPS points ?

xavierberlo — Fri, 29 Aug 2014 12:28:50 GMT

First of all, I'd like to thank you both for trying to help me, it is greatly appreciated because I really don't know what to do.

Dan, I've tried to access your document on onlinelibrary but it's a "buy to consult" and I use the computer at work and am not allowed to make any purchases online unless it is a tool that will do exactly what we need for this project and you said earlier that you haven't updaded your version to arcgis so would it be of any direct use for me ? Not trying to be picky but it has to be justified and to get permssion to buy something, it has to be THE tool that we need.

Riyas, thank you for this script. I tried to execute it but I have another problem that I'm not sure how to solve. The GPS points are taken 10meters (40 feet) away from each other and when I'm trying to reduce the scale at the closest I can to see separate points (1:0.004), one single point cannot be selected, the selection tool select a GPS point that is 30 points away from the one I selected ? Is there a way around it ? Because I cannot select the beginning, middle and end of a road. I have to select the road as a whole.

Again, thank you for your help.

Re: determine the radius of a curvature from GPS points ?

DanPatterson_Retired — Fri, 29 Aug 2014 12:47:50 GMT

The paper contains no code...and I can't locate my digital copy (If I have some success at work, I will forward it to you).
We were using high-end GPS, mounted in a trailer, to collect the data (and a "good driver" )

In principle, and going by memory, the following steps were used.

1 a road segment was selected (via various means), the segment may or may no contain a true curve, a threshold could be specified

2 straight lines segments were identified based upon a deviation parameter

3 the tangent segment from the straight line segment to the road curve was delineated

4 an initial assessment of the circular segment was determined...points that were within a tolerance were identified and collected

5 circular regression was applied to the points collected in step 4 to minimize the deviations from the curve and overcome the simplistic assessment of a 3-point circle

6 the exit segment (see 3) was determined

7 proceed with the next straight line segment or next tangent or next circular curve depending upon road layout.

I do have some python code and a toolbox that I was testing last year...if you can wait until after the labor day weekend (this weekend), I will get you a copy off if interested for testing purposes. My contact email can be found in my profile.

Re: determine the radius of a curvature from GPS points ?

RiyasDeen — Fri, 29 Aug 2014 12:51:01 GMT

Hi Dan,

Agree that 3 points along a larger section of road will not be a true representation of actual curvature of the road.

My understanding of xavier's requirement was he's interested in curvature for individual segment formed by 2 GPS points (which i understand is not possible) the next simplest option was to use 3 consecutive coordinates to measure the curvature.

I found your circular regression script here Circular Regression .

Re: determine the radius of a curvature from GPS points ?

DanPatterson_Retired — Fri, 29 Aug 2014 12:57:00 GMT

I have the newer python version in test phase now, this is only part of a larger problem as identified above. As indicated in the initial thread, there is a greater density of points available...hopefully along the curve segment. Accurate estimates of the radius of curvature in an engineering context has a different threshold of needs.

Re: determine the radius of a curvature from GPS points ?

xavierberlo — Fri, 29 Aug 2014 13:06:00 GMT

Good morning ! (depending on your location of course)

Thank you for your quick answers.

Yes Dan, I would be extremely interested and could wait until next tuesday. I don't know If I could send you the shapefile of the road I'm doing my tests on ? Maybe it could help you (as a whole) to understand really what my problem is. Reading your different steps, it seem to do what I need to do (but i'm far from an expert in that specific field). And we do use a very high-end GPS mounted on a econoline so it would seem to be close to what you did.

And Riyas, as it is now and if it cannot be changed / corrected, I cannot indeed select 2 points next to each other. I could select points but it is quite random (I can select one point every 20 or so points) BUT I actually do need to get the individual segment formed by 2 GPS points (or at least, as many GPS positions there is for a single curve). The whole idea would be to draw a road from those GPS points and within the road, having each curve and its radius in that road. It's a complicated task that I don't know if it can be done using ArcGis or if it would require other softwares like autocad.

I'm glad I found this forum to help me, this is giving me hopes

Re: determine the radius of a curvature from GPS points ?

RiyasDeen — Fri, 29 Aug 2014 13:49:57 GMT

Hi Xavier,

You'll need at least three points for calculating radius of curvature.

Important: The script I posted above is very simplistic. It assumes your circle passes through all the three points and does not take anything else into account. If this simplest interpretation of curvature would meet your need I'll modify the script to use selection from layer.

If one best fit radius of curvature for the whole road which takes all GPS points into account, Dan's script I referenced above is your best candidate.

Re: determine the radius of a curvature from GPS points ?

RiyasDeen — Fri, 29 Aug 2014 13:56:55 GMT

Hi Xavier,

Can you post a small subset of your data? Take out any confidential business attributes that you don't want to share.

If you don't want to reveal the actual location of your coordinate, omit the .prj file in you post.

Re: determine the radius of a curvature from GPS points ?

xavierberlo — Fri, 29 Aug 2014 14:15:10 GMT

Hello Riyas,

I don't mind sharing the data if it could help* me advance in the problem I have. Here is a segment of a road as a .zip file.

Thank you for your time.

Re: determine the radius of a curvature from GPS points ?

RiyasDeen — Fri, 29 Aug 2014 14:18:55 GMT

Open your discussion (not from inbox)
Reply
Use advanced Editor (top right)
Attach (bottom right)

Re: determine the radius of a curvature from GPS points ?

xavierberlo — Fri, 29 Aug 2014 14:25:22 GMT

Done, thank you. And to correct what I wrote earlier, there is one point every meter (4 feet)

Re: determine the radius of a curvature from GPS points ?

xavierberlo — Fri, 29 Aug 2014 14:42:23 GMT

Hi again,

Just to clear something out, when I said i need the individual of a segment formed by 2 GPS points, I actually "just" need the radius of one curve as a whole and not the radius of 3 GPS points within the same curvature. If the shape of one curve take 100 GPS points, I would need the radius of the curve from its beginning to the end and not for each set of 3 points within that same curve.

Re: determine the radius of a curvature from GPS points ?

RiyasDeen — Mon, 01 Sep 2014 01:52:37 GMT

Hi Xavier,

Attached script to calculate radius of curvature based on the points you select on the layer.

Setup:

Extract attached zip file.
Add a script tool and point it to radius of curvature.py
Set a script parameter source as Feature layer
Change Line 15 on radius of curvature to point to the circle shape file
Add your XY point layer to map and select set of points to calculate radius (If you don't select points then all the points will be used)
Script will calculate Radius of curvature using three point logic (first , middle and last point based on NoLigne field order of values) as well as Dan's Circular regression.
Circle feature class will have points which form the circle and type column with logic used for computing it.
Use the one that best fits your purpose.
Output would like below.

Note: CircularRegressionHelper.py is dan's code as is from Circular Regression

Re: determine the radius of a curvature from GPS points ?

DanPatterson_Retired — Mon, 01 Sep 2014 08:35:58 GMT

This will get you started, but the old version has been modified to deal with real world projected coordinates (ie in the 100,000s and 1,000,000s as would be the case for a UTM projection. the 3 point (aka linear solution) is simply there to provide an estimate of the center of the circle for the non-linear solution. It is the latter that is used to generate the circle. Prior to reporting results, you should test the results against known generated circular arcs with and without scatter normal to the curve but this should get you started.

Re: determine the radius of a curvature from GPS points ?

xavierberlo — Mon, 01 Sep 2014 13:33:17 GMT

wow thank you so much for this precious help.

I tried to compare the results from your script and the one I had using the curve calculator (advanced editing tool). To be able to use the curve calculator, I created a line shapefile and made 2 tangents and then drew the chord and then measured the chord and the arc distance between the 2 tangents. I'm well aware that it is very basic and maybe not very acurate but this was all I had before asking for help here and the results I have from your script seems to be similar from the one I had using the curve calculator. Of course, I will need to do more tests in order to see how acurate it is and if this will be enough for our needs (but I'm sure it is) but I wanted to thank you both for your help. I'll come back for a follow-up on my tests results later on.

Edit : Okay now I have different results. It's not per say a different result but rather -it appears- a different scale.

Here is what I have from the curve calculator and what I have using your script

As you can see, I get a radius of 283 using the curve calculator and 0.00270 or 0.00363 using your script. Is it just because of the scale used in your script ? Or is it really a different result ?

Edit2 : Well, now it appears I have a different result. Using the same method, here is what I have. I use the measure tool to measure the arc and chord distances. And of course, the highlighted points are the ones selected for the script. Is it again just the scale ?

Re: determine the radius of a curvature from GPS points ?

RiyasDeen — Mon, 01 Sep 2014 14:57:24 GMT

Hi Xavier,

Looks like curve calculator is giving results in linear units feet or meter. the script produces results in decimal degrees. You may want to project you points and try again. You can use project tool to project it to your local projected coordinate system

Re: determine the radius of a curvature from GPS points ?

xavierberlo — Mon, 01 Sep 2014 15:13:13 GMT

Hello Riyas,

I changed the coordinates to the one I use in a different shapefile which is GCS_WGS_1984 but it doesn't change anything. Should the coordinates be projected instead ? And to be honest, it would be better for our need to have the radius given in meters instead of decimal degrees. Is it something that can be easily modified in the script ?