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Posts Tagged ‘comparison’

Comparación de DTM usando Global Mapper 17.0.1

2016/02/12

Hagamos hoy algo sencillo, comparar, primero cualitativamente (visualmente) y después cuantitativamente dos DTM. Por un lado elegimos una fuente muy usual, SRTM de 3 arc sec (aproximadamente 90m) con un DTM derivado de Fotogrametría Stereo.

  • Comparación CUALITATIVA (i.e visual)
  • Comparación CUANTITATIVA (i.e RMSE)

Abrimos por un lado un DTM cuya fuente sea SRTM, en este caso me he conectado via WMS (Web Mapping Service) a través del data online disponible dentro de la misma aplicación Global Mapper (File/Download Online Imagery/data). La resolución es de aproximadamente 90m (3 arc sec).

DTM-COMPARISON-20160212

Por otro lado he encontrado este DTM cuya fuente conozco (Stereo Photogrammetry). La resolución es de 5m.

DTM-COMPARISON-20160212-02

A través de la herramienta ‘digitizer tool’ (Tools/Digitizer) seleccionamos una línea dibujada al azar sobre los dos. Botón derecho del ratón-> analysis/measurement/path profile. Exporto ambas imágenes (es importante en path setup definir un mismo mínimo y máximo para poder compararlas adecuadamente).

Con Photoshop superpongo (Layer display/ multiply) ambas imágenes y veo cuán diferente son.

DTM-COMPARISON-20160212-03

Esto nos da una primera idea de la comparación, pero vayamos un poco más allá: ¿Cuál es el RMSE (Error medio cuadrático, Root Mean Square Error) entre ambas bases de datos?.

DTM-COMPARISON-20160212-04

Esta es una medida de desviación que nos va a definir mucho más exactamente que una simple visualización. Podéis ver algo más desarrollado este punto en este link de esta misma página:

https://geovisualization.net/2010/06/30/using-excel-to-calculate-the-rmse-for-lidar-vertical-ground-control-points/

DTM-COMPARISON-20160212-05

Ahora tan solo hemos de verificar que esta cifra sea la correcta teniendo en cuenta los valores de precisión prometidos en la entrega.

Espero que os haya resultado interesante, si así es, no olvidéis comentar, compartir o simplemente decir Hola. Cualquiera de estas opciones es apreciada.

Un saludo cordial,
Alberto CONCEJAL
MSc GIS and Remote Sensing

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Comparing France Meteo and Spain Meteo from the visualization point of view

2014/11/24

After living in France for four years i have to tell i am always aware of Meteo information on TV (well, i live in Brittany, i guess this makes sense!). It was the same in Spain or anywhere else in the world where i had lived and the reason why is i have always loved Meteo and statistiques, mostly after working as an aerial surveying photographer in the late nineties… but that’s another history.

Weather forecast its quantitative data that distributes spatially, meaning every single spot will have a different figure, even if it’s separated no more than 1 mm, at least in theory. So the question is: as its impossible showing predictions for every single square mm of the area of interest, we need to estimate them using different models. Still if we point anywhere at the map we should know if the icon or figure applies or not to the spot i want to know about.

Let’s make it easier to understand, lets use images!!!

First of all, i know its difficult but it’s important, please don’t have into account Meteo news are presented (in this particular case) by Anaïs BAYDEMIR, which is a beautiful TV journalist at France 2… Let’s not focus on this (but if you happen to want to know more about her i hereby copy a couple of links to both wikipedia and youtube:

http://fr.wikipedia.org/wiki/Ana%C3%AFs_Baydemir

spain-meteo

Having said that, le’s take a look the way this is shown in Spain (TVE 2014). Well, again let’s not focus on the guy’s grey suit but…

 

 

 

 

 

spain-meteo-02

Information it’s kind of OK but what happens if we want to know about a spot in the middle of two icons?. Is the partly cloud icon which applies to my place or it’s the ‘sun and flies’ one?. How can i be sure of the forecast if i live in this this big region in the SW of Spain?…

 

 

 

 

france-meteo

On the other hand let’s focus on Anaïs_Baydemir, ops, meaning let’s focus on the way France 2 shows this information:

france-meteo-02

Every single square mm is perfectly defined, if we want to know the forecast in a particular place we know the icon that corresponds to the spot and we don’t have to guess…

france-meteo-03

I know it’s kind of nothing too important, mostly if introduced this saucy way but think about it, wouldn’t you prefer to read Meteo this way? (again i’m not asking if you prefer the way the french beauty is showing the info compared to the way the spanish guy does, that’s completely irrelevant… right?)

Regards,
Alberto CONCEJAL
MSc GIS and Meteo fan