topic Re: Measuring distances over time in Spatial Data Science Questions

Measuring distances over time

MarilenaKallweit — Mon, 12 Oct 2015 11:52:11 GMT

Hello community,

I have a problem analysing the data of my master thesis. Hopefully someone can help me.

I have tracked many dogs and their owners with GPS while hunting and now I want to measure the distances between these two "moving point objects" over time.

By now I load the GPS Data in ArcGIS and make a tracking layer out of it, so I can use the Playback Manager of the Tracking Analyst tool. I set it to 1 minute per second and go manually through it and measure the distance at every step per hand. This costs a lot of time, especially because I have a lot of these tracks.

So my question is: is there a solution to get a table or a graph of the distances between the two objects over time automatically? That would help me so much!

Thanks in advance,

Lena

Re: Measuring distances over time

NeilAyres — Mon, 12 Oct 2015 12:40:49 GMT

Couldn't you use some variant of the code posted here by Dan Patterson..

Calculate Distance.

Re: Measuring distances over time

MarilenaKallweit — Tue, 13 Oct 2015 09:27:04 GMT

The approach seems about right. But as I am new to Python I don't see how I can implement the time in that code.

Re: Measuring distances over time

NeilAyres — Tue, 13 Oct 2015 09:44:25 GMT

Well, that post was in answer to another question from a user here. About distances between street poles or something.

If you want further guidance, I think you should be a little more specific about your data, its attributes and exactly what you want to achieve.

Re: Measuring distances over time

DanPatterson_Retired — Tue, 13 Oct 2015 10:21:20 GMT

Since you have gps data, I presume that you have the coordinates of the values. Suggested workflow

get your data into a projected coordinate system (use the Project tool) so that you have planar/Euclidean coordinates
follow the instructions in the fuller post on working with points it provides more details on the setup
once you have the distances, either inter-point or cumulative for example then you can equate those to your time data.

I presume you can get delta time from the time data if needed, but the cumulative values will facilitate graphing

Addition

Have you ruled out the time tools listed here from the tracking analyst toolbox?

Re: Measuring distances over time

MarilenaKallweit — Mon, 19 Oct 2015 07:07:59 GMT

That doesn't really help me for I don't need the distances between points of the same track but between two points of two different tracks at the same time.

Re: Measuring distances over time

DanPatterson_Retired — Mon, 19 Oct 2015 07:28:29 GMT

Ahhh. I presume then, that you have examined the time data and ruled out joining the tables based upon a common time? I doubt a simple join will exist, so it might be worthwhile to parse/summarize your data into some common time increment. Once that has been established then the feature location at those times could be derived. Do you have an example of two files (a small sample) to show the form of the data?

Re: Measuring distances over time

NeilAyres — Mon, 19 Oct 2015 07:47:05 GMT

Ah, I see.

I don't know of any ArcGIS tools to do this, as its nots really a spatial problem but more of a time stamp matching problem.

I have done this in the past for correcting geophysical readings (rover vs base station) and basically did the matching in Access by finding the minimum time difference between records in each file. And I suppose we could also do this in python as well.

But some example files would be a help.

Re: Measuring distances over time

MarilenaKallweit — Wed, 21 Oct 2015 15:57:12 GMT

These are the original records in format gpx. I can save them separately (the first and the second) or together (the third). They are not edited in ArcGis by now. How would you proceed with it?

Re: Measuring distances over time

NeilAyres — Thu, 22 Oct 2015 08:44:55 GMT

Thanks for the data, I had a fiddle with it.

First I used the dnr garmin program to read the gpx track files to points (as text & shapefiles).

Then I created a personal geodb (access) and loaded the data from text.

Unfortunately, the time stamp info in each file (ltime), won't automatically come in as a time/date field, have to first import it as text, then update it into a newly created TimeStamp field of time/date type. Confusing huh...

As I said previously, you can create a series of queries which join one file to the other based on a minimum time difference between them.

Have a look in the mdb file zipped attached.

From the matched table I used the XY table to line tool to create the joining lines. Then added a distance field, changed the projection of the df to UTM32N and calculated a metres distance / length.

Hope this works for you.

Re: Measuring distances over time

MarilenaKallweit — Fri, 23 Oct 2015 07:24:22 GMT

Thank you for the effort. That sounds very promising! I will try it over the weekend and report.

Re: Measuring distances over time

NeilAyres — Fri, 23 Oct 2015 07:45:45 GMT

If you need further guidance about the queries in the mdb or anything else, post here....

Good luck.

Re: Measuring distances over time

MarilenaKallweit — Tue, 27 Oct 2015 08:23:01 GMT

I only worked with your tables by now to see if I get it with ArcMap. Everything worked in the attribute table, but I don't see the lines on the map. That is not a big Problem, but maybe you can tell me what I do wrong.

I got an Access account from the University now. It's been a while since I worked with that kind of software. So I would really appriciate a little help with the queries, because I don't even know how to start.

Re: Measuring distances over time

NeilAyres — Tue, 27 Oct 2015 10:36:13 GMT

This is the view of the TimeMatching.mdb in ArcCatalog.

The lines are the feature class LinkedLines. You should be able to see that and load it into ArcMap.

Will post more detail on the queries in access shortly

Re: Measuring distances over time

NeilAyres — Tue, 27 Oct 2015 10:56:32 GMT

This inside Access.

We are joining Chef (dogs - 2250 records) back to Kallweit (owner - 1306 records).

First we create a query which "joins" the 2 input tables (tblChefGPXDataPoints @ tblKallweitGPXDataPoints).

Because there is no "join" as such, this just creates a very large / long cross product of the 2 tables.

Then query 2, summarises this query across the ChefID and the minimum time.

Then query 3, joins this back to the first (a bit circular) so we can find the IDs on both sides.

Query 4, then uses this as a join in between the original input tables so we can get back to the Lat/Longs on both sides.

Hope this makes some sort of sense.

Do you have any folk there who know a little about Access?

Re: Measuring distances over time

MarilenaKallweit — Mon, 02 Nov 2015 13:43:29 GMT

Thank you so much!

It took a while, but know I got it. It's a little bit easier for me, because Access 2013 recognizes the ltime field as date/time field. So I don't have to add an extra TimeStamp.

It is exactly what I need. Now I can finally go on with my work Thanks again!

Re: Measuring distances over time

NeilAyres — Tue, 03 Nov 2015 07:25:54 GMT

Marilena,

good to hear that this works for you.

Good luck with the rest of the study.