topic Re: Scatter plot of two rasters in Python Questions

Scatter plot of two rasters

ShouvikJha — Sun, 12 Dec 2021 02:18:31 GMT

Xander Bakker‌ and Dan Patterson‌ , Kindly your cooperation is highly appreciate.

I have two raster file, i want to perform Scatter plot of those raster . I found one code that is written by Dan Patterson‌

Below code

from matplotlib import pyplot as plt
xs = [1,3,2,5,6,4] # Which fomart of data i have to give here?
ys = [3,2,1,5,3,2]
plt.scatter(xs, ys)
main_title ="My first graph"
plt.title(main_title, loc='center')  #loc is either left, right or center
plt.minorticks_on()
plt.tick_params(which='major', direction='in', length=6, width=2)
plt.tick_params(which='minor', direction='in', length=4, width=2)
plt.show()‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Earlier Dan suggest to someone convert those raster to arrays. I followed the same but could not solve it. How to process tiff to array.

how do i execute two raster in X and Y axis. I have tiff images.

Branched from Perform Raster Calculation from Multiple Sub-folder Using ArcPy

Re: Scatter plot of two rasters

DanPatterson_Retired — Tue, 11 Oct 2016 08:06:25 GMT

you have to plot them separately as rasters not as a scatter plot, you can convert a raster to rows and columns and plot those as a scatterplot, so I am not sure what you want to do specifically. What does your data look like now?

Re: Scatter plot of two rasters

NeilAyres — Tue, 11 Oct 2016 12:02:44 GMT

I would normally not do this on the entire raster or rasters but create a random subset of them using Create Random points and then use Sample.

Then just use the graphing tools inside ArcMap.

Re: Scatter plot of two rasters

ShouvikJha — Tue, 11 Oct 2016 12:49:09 GMT

Dan Patterson‌

Thank you. I want to do on cell by cell basis. I have two different parameters of raster data, so one parameter i want to plot in X axis and another one Y axis to make it relation between two parameters.

How do i convert it in row and column format. can i convert it in ASCII format?

Data is tiff format same as which we got from our above scrip suggested by xander_bakker‌

Re: Scatter plot of two rasters

ShouvikJha — Tue, 11 Oct 2016 12:52:37 GMT

Reply from Dan Patterson‌

before you go off into a side tangent of graphing and trying to 'correlate', 'predict' or extrapolate see...

Geographically Weighted Regression (GWR)—Help | ArcGIS for Desktop

Only if you are working with interval/ratio and there is some real predictive behaviour between the two variables. Looking for correlations, relationships between two variables via a magical statistical test is overused. But if you are looking for an association then the above and other substitutes will save a flurry of activity in the wrong direction

For nominal data... Combine—Help | ArcGIS for Desktop gives you the basis for tests of Association such as the chi-squared test. And at worst it gives you a tabular output for discussion

Make your intent clear and specific... otherwise people with keep throwing suggestions out that will meet vague goals ... not necessary specific ones.

Re: Scatter plot of two rasters

ShouvikJha — Tue, 11 Oct 2016 12:53:37 GMT

Thank you. I am not getting your points. i am trying plot two variable of raster like this ...

Re: Scatter plot of two rasters

ShouvikJha — Tue, 11 Oct 2016 12:54:06 GMT

Reply from Dan Patterson‌

If the rasters aren't huge convert to points, then Ordinary Least Squares (OLS)—Help | ArcGIS for Desktop I think the report allows for a graph

Re: Scatter plot of two rasters

ShouvikJha — Tue, 11 Oct 2016 12:58:49 GMT

Xander Bakker‌, Dan Patterson‌ , I moved total conversion from there to here. Please cooperate with us. Sorry for the inconvenience cause.

Re: Scatter plot of two rasters

ShouvikJha — Tue, 11 Oct 2016 13:01:59 GMT

Dan Patterson‌, As your last comment we have huge data point. number of columns and rows 2737, 2025 respectively. So whats is the best way to plot those raster.

Re: Scatter plot of two rasters

XanderBakker — Tue, 11 Oct 2016 13:53:17 GMT

I think the suggestion by Neil Ayres is an option you should look at. Use Create Random Points—Help | ArcGIS for Desktop , followed by Extract Multi Values to Points—Help | ArcGIS for Desktop to graph the two variables (rasters) together in a scatter plot.

The alternative is using numpy to access the pixel values and create a resulting table with the combination of the values for each cell. In your case that would be over 5.5 M records, which might yield errors.

Re: Scatter plot of two rasters

ShouvikJha — Tue, 11 Oct 2016 14:07:28 GMT

xander_bakker‌, Thank you. For my case i need to compare all the pixels corresponding to same latitude and longitude.

Re: Scatter plot of two rasters

DanPatterson_Retired — Tue, 11 Oct 2016 17:48:57 GMT

Follow Neil's and Xander's advice. A plot like that is going to show nothing more than a scaled down version. Calculate the statistical parameters of both variables and summarize in tabular form. This is a classic example of a graph adding nothing to the analysis or presentation. In fact, the association between the variables is better shown in mapped form since the spatial dimension is explicit.

Is this a requirement for some project? If so, gently suggest to the proponent that better means of examining the relationship are available.

Re: Scatter plot of two rasters

ShouvikJha — Tue, 11 Oct 2016 18:10:25 GMT

Dan Patterson Thank you. Yes . This graph require for my research project. I am PhD scholar. I am going to publish a paper How Temperate effects on vegetation growth. So i want a scatter diagram between two variable so i can say to research community by the statistical plot.

I have done this task suggestion by you Xander Bakker‌ and @Neil Ayres.

Thank you very much.

Re: Scatter plot of two rasters

XanderBakker — Sun, 12 Dec 2021 02:18:33 GMT

Hi shouvik jha ,

Just to give an example of how you could combine the Neil Ayres suggestion with the snippet Dan Patterson posted earlier, using two raster from the data you attached earlier (2010 r001_NPP vs r005_NPP):

def main():
    import arcpy
    import os
    import math
    from matplotlib import pyplot as plt

    ras1 = r'D:\Xander\GeoNet\MeanRasters\data\r001_NPP.TIF'
    ras2 = r'D:\Xander\GeoNet\MeanRasters\data\r005_NPP.TIF'
    fc_pnt = r'D:\Xander\GeoNet\MeanRasters\gdb\data.gdb\randompoints'
    num_points = 1000

    # minimum distance between points to avoid points in same pixel
    min_dist = math.hypot(arcpy.Describe(ras1).meanCellHeight, arcpy.Describe(ras1).meanCellWidth)

    # Create random points
    ws, fc_name = os.path.split(fc_pnt)
    arcpy.CreateRandomPoints_management(out_path=ws, out_name=fc_name,
                                        constraining_extent=ras1,
                                        number_of_points_or_field=num_points,
                                        minimum_allowed_distance=min_dist)

    # Extract Multi Values to Points
    arcpy.CheckOutExtension("Spatial")
    ws, ras1_name = os.path.split(ras1)
    ws, ras2_name = os.path.split(ras2)
    ras1_name = ras1_name.replace('.', '_')
    ras2_name = ras2_name.replace('.', '_')
    in_rasters = [[ras1, ras1_name], [ras2, ras2_name]]
    arcpy.sa.ExtractMultiValuesToPoints(fc_pnt, in_rasters, "NONE")
    arcpy.CheckInExtension("Spatial")

    # create lists of values
    xs = [r[0] for r in arcpy.da.SearchCursor(fc_pnt, (ras1_name)) if not r[0] is None]
    ys = [r[0] for r in arcpy.da.SearchCursor(fc_pnt, (ras2_name)) if not r[0] is None]

    # create plot
    plt.scatter(xs, ys)
    main_title ="Scatter plot of {0} vs {1}".format(ras1_name, ras2_name)
    plt.title(main_title, loc='center')  
    plt.minorticks_on()
    plt.show()

if __name__ == '__main__':
    main()
‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Which yields this:

Below the point distribution in ArcGIS:

Grey points are filtered out for the graphic since they have NULL values.

Re: Scatter plot of two rasters

ShouvikJha — Sun, 12 Dec 2021 02:18:36 GMT

Xander Bakker‌. Thank you. Excellent idea. Really its very helpful for research community.

I have created random points (Number of points:1000) using create random tool under feature class. and I have given that point feature class as fc_pnt path,

fc_pnt = r'D:\TEST\Reference_RASTER\Random_Points\Random_pnts.shp'‍

i am getting error, might be i didn't construct fc_pnt data properly

Traceback (most recent call last):
  File "<module1>", line 45, in <module>
  File "<module1>", line 34, in main
RuntimeError: A column was specified that does not exist.‍‍‍‍

Hope i have problem with my point feature data set. may i know how to construct that point feature class.

Thank you.

Re: Scatter plot of two rasters

DanPatterson_Retired — Wed, 12 Oct 2016 06:36:42 GMT

The parameters are convoluted, and I suspect that you didn't follow all of them since you specified a constraining extent and a total number of points.. did you do the dissolve? Did you try it without the optional parameters specified? see Create Random Points—Help | ArcGIS for Desktop

Re: Scatter plot of two rasters

ShouvikJha — Wed, 12 Oct 2016 07:38:16 GMT

Dan Patterson‌. Thank you. Firstly i tried without dissolve, after read your comment i tried dissolve also, but problem still persist.

I just explaining short what i am doing,

Firstly i created random points using create random points tool----------> After i copied that Random points path directly from folder and use as "fc_pnt" path --------> Run the script

I have noticed, while running the program it is generating same point file in same location,

I have followed dissolve also after generating random points but same error i am getting.

Re: Scatter plot of two rasters

NeilAyres — Wed, 12 Oct 2016 11:38:58 GMT

To specify the inputs to the tool, just use the little envelope on the right of each input box and navigate to the data using that.

Re: Scatter plot of two rasters

ShouvikJha — Wed, 12 Oct 2016 15:45:37 GMT

Neil, Thank you. Can you give one example ?

Re: Scatter plot of two rasters

XanderBakker — Fri, 14 Oct 2016 17:11:57 GMT

Hi shouvik jha ,

I had this type of error before too. Could you tell me the names of the rasters that you are using?

In my case I had this error since I used the name of the raster for the output fields. The problem was that the name "something.tif" was not valid as field name (renamed automagically by ArcGIS) resulting in trying to access a field name that does not exist. I "corrected" this in the code by replacing the dot for a underscore, buy obviously this would require something more elaborated to get a completely valid field name. Try and use ValidateTableName—Help | ArcGIS for Desktop for a more stable solution.