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determine the radius of a curvature from GPS points ?

xavierberlo

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

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DanPatterson_Retired

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

RiyasDeen

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.

coords.csv.zip

radius of curvature.py.zip

DanPatterson_Retired

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.

xavierberlo

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.

DanPatterson_Retired

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.

RiyasDeen

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 .

DanPatterson_Retired

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.

xavierberlo

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

DanPatterson_Retired

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.

xavierberlo

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 ?

RiyasDeen

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

xavierberlo

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 ?

DanPatterson_Retired

The old toolset should only be applied to projected data. There are some issues that were addressed in newer versions which aren't posted anywhere since I am still waiting for ArcScript 2.0 to appear.

Timothy Hales‌ Jim Barry‌

DanPatterson_Retired

Everyone has pictures except me

RafaeldePedro_1-1748507394302.png

JakeSkinner_0-1748515818533.png

Subdivisions.jpg

DanPatterson_Retired

In the last image sent by Riyas, you are picking too many points, you are getting points of the tangent thingy (can't remember what it is called Xavier) you should be able to chose about 60% of the points that you have chosen. A good test is to visually eye the centre of the arc (there are other methods) then select some points, do the results then gradually trim points off either end of the selection. In theory, there should be a place where point selection doesn't improve radius estimates and the only deviations will be due to scatter normal (90 degrees) to the "real" arc. If memory serves, this scatter has a great role upon the estimates of the radius. I am still trying to track down copies of the paper and a thesis which deals with this issue. I can't find my copies and my colleague isn't back yet.

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