topic Re: Multiple Ring Buffer displays 2.5 Km polyline within 30 metres ring? in Spatial Data Science Questions

Multiple Ring Buffer displays 2.5 Km polyline within 30 metres ring?

SebastianSalazar — Wed, 30 Jul 2014 05:56:11 GMT

Hello folks.

In Arc Map 10.1 I have I polyline with distances (2.659542 m) and length (0.00266 km) fields. Those fields were calculated with geomtric calculator.

I am tryin a Multiple Ring Buffer Tool with 30, 50 and 100 metres of distance. At the end, the tool shows 3 rings, however,

2.5 Km polyline is located within the 30 metres ring (see littel blue polyline in inner ring). I am really confused. Why 30 metres ring is larger than polyline length?

The polyline is in WGS 1984 World Mercator.

Can you give an idea(s) to fix this problem?

Re: Multiple Ring Buffer displays 2.5 Km polyline within 30 metres ring?

DanPatterson_Retired — Wed, 30 Jul 2014 07:44:37 GMT

your polyline appears to be meters or degrees. Do not use unprojected data when determining buffers unless you want to calculate geodesic buffers which should be oval. Project your data if you want to work in Euclidean space

Re: Multiple Ring Buffer displays 2.5 Km polyline within 30 metres ring?

SebastianSalazar — Wed, 30 Jul 2014 14:12:14 GMT

Hello Dan. Thanks for your reply

The shp file I am working is in Guatemala. My problem. I don't have the GTM Coordinate System for Guatemala

to define the projection. I spent hours and hours googling, but no succes.

I am not sure how to do your recommendation. Could you help me to define the projection and project the shp?

I enclose the ca-9 shp file.

Thanks againg

Re: Multiple Ring Buffer displays 2.5 Km polyline within 30 metres ring?

DanPatterson_Retired — Wed, 30 Jul 2014 14:22:59 GMT

I am not sure, but I will cc the one person who would know...

Melita Kennedy‌

Re: Multiple Ring Buffer displays 2.5 Km polyline within 30 metres ring?

SebastianSalazar — Wed, 30 Jul 2014 14:29:57 GMT

Dan. Many thanks.

Re: Multiple Ring Buffer displays 2.5 Km polyline within 30 metres ring?

MelitaKennedy — Wed, 30 Jul 2014 17:48:24 GMT

Here's a link to GTM: Guatemala Transversa - IGN‌

PROYECCION: Transversa de Mercator (tipo Gauss Kruger) en una zona única local.
ELIPSOIDE: WGS84.
LONGITUD DE ORIGEN: 90°30' (meridiano central de proyección).
LATITUD DE ORIGEN :0° (el Ecuador)
UNIDADES: Metros.
FALSO NORTE: 0 metros.
FALSO ESTE: 500,000 metros en el meridiano central.
FACTOR DE ESCALA EN EL MERIDIANO CENTRAL: 0.9998
NUMERACI0N DE LAS ZONAS: No esta dentro de la numeración normal de zonas UTM. Se le puede llamar zona 15.5.
NUEVO SISTEMA DE REFERENCIA GEODESICO: WGS84 preciso, basado en ITRF94 época 1997.5 parámetros del elipsoide

- semieje mayor 6378137.0 metros

- semieje menor 6356752.3142,

- achatamiento = 1/298.257223563.

Below is a well-known text version of the coordinate reference system. Copy it into a .txt file, and make sure it is a single line. Copy the text file and name it gua_ca9.prj. Put it with the other gua_ca9 files.

PROJCS["WGS_1984_Guatamala_TM",GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",500000.0],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-90.5],PARAMETER["Scale_Factor",0.9998],PARAMETER["Latitude_Of_Origin",0.0],UNIT["Meter",1.0]]

Melita

Re: Multiple Ring Buffer displays 2.5 Km polyline within 30 metres ring?

SebastianSalazar — Wed, 30 Jul 2014 20:45:46 GMT

Hello Melita. Many thanks for your help

I did your recommendation. The first time I runned the MRB and nothing happened. Then I checked the code again and I only corrected the word Guatamala for Guatemala.

I runned the MRB againg and the 30 metres ring still displays de polyline. I am confused and not familiar with fixing projection. What I am doing wrong.

Cheer's

Re: Multiple Ring Buffer displays 2.5 Km polyline within 30 metres ring?

MelitaKennedy — Wed, 30 Jul 2014 21:03:25 GMT

Hi,

You might try projecting your data to GTM. That will give you a new shapefile/feature class that's projected. Then create the buffers again.

Melita

Re: Multiple Ring Buffer displays 2.5 Km polyline within 30 metres ring?

SebastianSalazar — Wed, 30 Jul 2014 22:28:36 GMT

Melita. I really apologyze for my low expertise in Projection.

I tested the shp file with Coordinate System <Undefined>

First from Projections and Transformation I used Project Tool from Feature, but the Input

Dataset or Feature Class diplays the little red x circle. So I close the tool

With Define Projection Tool I selected the shp and in Coordinate Ssytem I selecte GTM. Then I run the MRB and shp file is little in the 3o metres ring

With Create Custom Geographical Transformation Tool. I don't what data I have to enter or select.

I enclose the shp file with Coordinate System <Undefined> including the .txt file from previous message, hoping that you could help me. Please

Thanks againg

Re: Multiple Ring Buffer displays 2.5 Km polyline within 30 metres ring?

MelitaKennedy — Wed, 30 Jul 2014 22:32:30 GMT

Hello Sebastian,

I was not very clear in my earlier reply. Use Define Projection to set the geographic coordinate system for your data. It's in decimal degrees. Try using WGS 1984 first (it's in Geographic Coordinate Systems, World). Then use the Project tool to create a new dataset that's in GTM.

Melita

Note: The data could be in NAD 1927 instead.

Re: Multiple Ring Buffer displays 2.5 Km polyline within 30 metres ring?

IanMurray — Wed, 30 Jul 2014 22:47:01 GMT

Sebastian Salazar wrote:

Hello folks.

In Arc Map 10.1 I have I polyline with distances (2.659542 m) and length (0.00266 km) fields. Those fields were calculated with geomtric calculator.

I am tryin a Multiple Ring Buffer Tool with 30, 50 and 100 metres of distance. At the end, the tool shows 3 rings, however,

2.5 Km polyline is located within the 30 metres ring (see littel blue polyline in inner ring). I am really confused. Why 30 metres ring is larger than polyline length?

The polyline is in WGS 1984 World Mercator.

Can you give an idea(s) to fix this problem?

I think you may have answered your own question. Accoding to your original post, you line is only 2.659m, not kilometers(or as you mentioned .00266km). I'm assuming you are only working with a single line, not multiple lines anytime you buffer a feature, the resulting buffer by definition should contain your input feature(unless you are using a negative value buffer). So yes, your 2.659m polyline should be within your 30m radius buffer.

Re: Multiple Ring Buffer displays 2.5 Km polyline within 30 metres ring?

SebastianSalazar — Wed, 30 Jul 2014 22:55:24 GMT

Melita. Now the MRB is working as expected.

Thank you very much indeed.

Re: Multiple Ring Buffer displays 2.5 Km polyline within 30 metres ring?

SebastianSalazar — Wed, 30 Jul 2014 22:59:54 GMT

Ian.

Using the recommended process from Melinda, now the MRB is working.

Many thanks for your reply.

Cheer's