Why does my data not show up?

Question

Anne-Marie 2023-7-28

0
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https://ww2.mathworks.cn/matlabcentral/answers/2001957-why-does-my-data-not-show-up

评论： Walter Roberson 2023-7-28

Hi. I am trying to write a code that displays shapefiles with data on it on a basemap and have a set of grid boxes that go over the shapefile (benthic) and count the amount of data points in each box. Most of it works, however the boxes don't cover the entire benthic region and it says that there are no data points in the boxes when there are. I attached a snippet of code that is supposed to do just those things but it's not. Is there something that I'm missing that is the reason why it's not working?? Any help or tips would be much appreciated!! Thank you.

Code:

% Initialize variables to store class counts in each grid cell
numLatCells = length(latGrid) - 1;
numLonCells = length(lonGrid) - 1;
classCountsInGridCell = cell(numLatCells, numLonCells);
% Calculate the actual cell size based on the new number of grid cells
actualCellSize = 1 / (111.32 * 1000); % 1 degree of latitude is approximately 111.32 km or 111,320 meters
cellSizeLat = (latLimits(2) - latLimits(1)) / numLatCells;
cellSizeLon = (lonLimits(2) - lonLimits(1)) / numLonCells;
% Create a matrix to store grid cell information
gridMatrix = zeros(numLatCells, numLonCells, 'int16');
% Create a grid of latitude and longitude values covering the entire map extent
latGrid = linspace(latLimits(1), latLimits(2), numLatCells + 1);
lonGrid = linspace(lonLimits(1), lonLimits(2), numLonCells + 1);
% Repeat over each cell in the grid and store class attributes if within the benthic area
for i = 1:numLatCells
    for j = 1:numLonCells
        % Find the data points within the current grid cell
        inGridCell = lat >= latGrid(i) & lat < latGrid(i+1) & lon >= lonGrid(j) & lon < lonGrid(j+1);
        
        % Check if any data points fall within the benthic shapefile
        if sum(inGridCell) > 0
            gridMatrix(i, j) = 1;
        end
    end
end
% Plot the boxes on the map
hold on;
gridCounter = 1; % Initialize grid counter
for i = 1:numLatCells
    for j = 1:numLonCells
        if gridMatrix(i, j) ~= 0
            % Define the grid cell corners as a polygon
            latPolygon = [latGrid(i), latGrid(i+1), latGrid(i+1), latGrid(i), latGrid(i)];
            lonPolygon = [lonGrid(j), lonGrid(j), lonGrid(j+1), lonGrid(j+1), lonGrid(j)];
            
            % Plot the grid cell as a polygon without adding to the legend
            geoplot(ax, latPolygon, lonPolygon, 'Color', 'k', 'LineWidth', 1, 'HandleVisibility', 'off');
            
            % Get the center of the current grid cell
            boxCenterLat = (latGrid(i) + latGrid(i+1)) / 2;
            boxCenterLon = (lonGrid(j) + lonGrid(j+1)) / 2;
            
            % Get the distance from the box center to Pinatubo's summit
            distanceToSummit = deg2km(distance(summitLat, summitLon, boxCenterLat, boxCenterLon));
            
            % Display the distance for the current grid cell
            text(boxCenterLat, boxCenterLon, sprintf('%.2f km', distanceToSummit), 'Color', 'red', 'HorizontalAlignment', 'center');
            
            % Check if the grid cell is within the benthic area
            if ~isempty(classAttributesInGridCell{i, j})
                % Get the class attributes for the current grid cell
                cellClassAttribute = classAttributesInGridCell{i, j};
                
                % Count the unique classes and their occurrences in the current grid cell
                [cellUniqueClasses, cellClassCounts] = uniqueCount(cellClassAttribute);
                
                % Display the result for the current grid cell
                fprintf('Grid %d:\n', gridCounter);
                fprintf('Class Counts:\n');
                for k = 1:numel(uniqueClasses)
                    classIndex = find(strcmp(cellUniqueClasses, uniqueClasses(k)));
                    if isempty(classIndex)
                        fprintf('%s: %d\n', uniqueClasses{k}, 0);
                    else
                        fprintf('%s: %d\n', uniqueClasses{k}, cellClassCounts(classIndex));
                    end
                end
                fprintf('\n');
            else
                fprintf('Grid %d:\n', gridCounter);
                fprintf('No data points in this grid cell.\n\n');
            end
            
            % Increment grid counter
            gridCounter = gridCounter + 1;
        end
    end
end
hold off;

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Walter Roberson 2023-7-28

We do not know anything about classAttributesInGridCell .

We could hypothesize that maybe it is the transpose of what you are expecting -- that maybe its first index is long rather than lat.

Note: you should consider optimizing your code. There are a series of calculations that do not need to be done if classAttributesInGridCell{i,j} is empty.

Also, instead of your loop building gridMatrix you could probably use histogram2 to get the counts per bin and then gridMatrix would just be (per_bin_count > 0) which could be further optimized to gridMatrix = logical(per_bin_count)

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Why does my data not show up?

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